* [PATCH v6 12/20] mm: shmem: allow freezing inode mapping
From: Pasha Tatashin @ 2025-11-15 23:33 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
From: Pratyush Yadav <ptyadav@amazon.de>
To prepare a shmem inode for live update via the Live Update
Orchestrator (LUO), its index -> folio mappings must be serialized. Once
the mappings are serialized, they cannot change since it would cause the
serialized data to become inconsistent. This can be done by pinning the
folios to avoid migration, and by making sure no folios can be added to
or removed from the inode.
While mechanisms to pin folios already exist, the only way to stop
folios being added or removed are the grow and shrink file seals. But
file seals come with their own semantics, one of which is that they
can't be removed. This doesn't work with liveupdate since it can be
cancelled or error out, which would need the seals to be removed and the
file's normal functionality to be restored.
Introduce SHMEM_F_MAPPING_FROZEN to indicate this instead. It is
internal to shmem and is not directly exposed to userspace. It functions
similar to F_SEAL_GROW | F_SEAL_SHRINK, but additionally disallows hole
punching, and can be removed.
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
include/linux/shmem_fs.h | 17 +++++++++++++++++
mm/shmem.c | 12 +++++++++++-
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 650874b400b5..a9f5db472a39 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -24,6 +24,14 @@ struct swap_iocb;
#define SHMEM_F_NORESERVE BIT(0)
/* Disallow swapping. */
#define SHMEM_F_LOCKED BIT(1)
+/*
+ * Disallow growing, shrinking, or hole punching in the inode. Combined with
+ * folio pinning, makes sure the inode's mapping stays fixed.
+ *
+ * In some ways similar to F_SEAL_GROW | F_SEAL_SHRINK, but can be removed and
+ * isn't directly visible to userspace.
+ */
+#define SHMEM_F_MAPPING_FROZEN BIT(2)
struct shmem_inode_info {
spinlock_t lock;
@@ -186,6 +194,15 @@ static inline bool shmem_file(struct file *file)
return shmem_mapping(file->f_mapping);
}
+/* Must be called with inode lock taken exclusive. */
+static inline void shmem_i_mapping_freeze(struct inode *inode, bool freeze)
+{
+ if (freeze)
+ SHMEM_I(inode)->flags |= SHMEM_F_MAPPING_FROZEN;
+ else
+ SHMEM_I(inode)->flags &= ~SHMEM_F_MAPPING_FROZEN;
+}
+
/*
* If fallocate(FALLOC_FL_KEEP_SIZE) has been used, there may be pages
* beyond i_size's notion of EOF, which fallocate has committed to reserving:
diff --git a/mm/shmem.c b/mm/shmem.c
index 1d5036dec08a..05c3db840257 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1292,7 +1292,8 @@ static int shmem_setattr(struct mnt_idmap *idmap,
loff_t newsize = attr->ia_size;
/* protected by i_rwsem */
- if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
+ if ((info->flags & SHMEM_F_MAPPING_FROZEN) ||
+ (newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
(newsize > oldsize && (info->seals & F_SEAL_GROW)))
return -EPERM;
@@ -3289,6 +3290,10 @@ shmem_write_begin(const struct kiocb *iocb, struct address_space *mapping,
return -EPERM;
}
+ if (unlikely((info->flags & SHMEM_F_MAPPING_FROZEN) &&
+ pos + len > inode->i_size))
+ return -EPERM;
+
ret = shmem_get_folio(inode, index, pos + len, &folio, SGP_WRITE);
if (ret)
return ret;
@@ -3662,6 +3667,11 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
inode_lock(inode);
+ if (info->flags & SHMEM_F_MAPPING_FROZEN) {
+ error = -EPERM;
+ goto out;
+ }
+
if (mode & FALLOC_FL_PUNCH_HOLE) {
struct address_space *mapping = file->f_mapping;
loff_t unmap_start = round_up(offset, PAGE_SIZE);
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 13/20] mm: shmem: export some functions to internal.h
From: Pasha Tatashin @ 2025-11-15 23:33 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
From: Pratyush Yadav <ptyadav@amazon.de>
shmem_inode_acct_blocks(), shmem_recalc_inode(), and
shmem_add_to_page_cache() are used by shmem_alloc_and_add_folio(). This
functionality will also be used in the future by Live Update
Orchestrator (LUO) to recreate memfd files after a live update.
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
mm/internal.h | 6 ++++++
mm/shmem.c | 10 +++++-----
2 files changed, 11 insertions(+), 5 deletions(-)
diff --git a/mm/internal.h b/mm/internal.h
index 1561fc2ff5b8..4ba155524f80 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1562,6 +1562,12 @@ void __meminit __init_page_from_nid(unsigned long pfn, int nid);
unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
int priority);
+int shmem_add_to_page_cache(struct folio *folio,
+ struct address_space *mapping,
+ pgoff_t index, void *expected, gfp_t gfp);
+int shmem_inode_acct_blocks(struct inode *inode, long pages);
+bool shmem_recalc_inode(struct inode *inode, long alloced, long swapped);
+
#ifdef CONFIG_SHRINKER_DEBUG
static inline __printf(2, 0) int shrinker_debugfs_name_alloc(
struct shrinker *shrinker, const char *fmt, va_list ap)
diff --git a/mm/shmem.c b/mm/shmem.c
index 05c3db840257..c3dc4af59c14 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -219,7 +219,7 @@ static inline void shmem_unacct_blocks(unsigned long flags, long pages)
vm_unacct_memory(pages * VM_ACCT(PAGE_SIZE));
}
-static int shmem_inode_acct_blocks(struct inode *inode, long pages)
+int shmem_inode_acct_blocks(struct inode *inode, long pages)
{
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
@@ -435,7 +435,7 @@ static void shmem_free_inode(struct super_block *sb, size_t freed_ispace)
*
* Return: true if swapped was incremented from 0, for shmem_writeout().
*/
-static bool shmem_recalc_inode(struct inode *inode, long alloced, long swapped)
+bool shmem_recalc_inode(struct inode *inode, long alloced, long swapped)
{
struct shmem_inode_info *info = SHMEM_I(inode);
bool first_swapped = false;
@@ -861,9 +861,9 @@ static void shmem_update_stats(struct folio *folio, int nr_pages)
/*
* Somewhat like filemap_add_folio, but error if expected item has gone.
*/
-static int shmem_add_to_page_cache(struct folio *folio,
- struct address_space *mapping,
- pgoff_t index, void *expected, gfp_t gfp)
+int shmem_add_to_page_cache(struct folio *folio,
+ struct address_space *mapping,
+ pgoff_t index, void *expected, gfp_t gfp)
{
XA_STATE_ORDER(xas, &mapping->i_pages, index, folio_order(folio));
unsigned long nr = folio_nr_pages(folio);
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 14/20] liveupdate: luo_file: add private argument to store runtime state
From: Pasha Tatashin @ 2025-11-15 23:34 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
From: Pratyush Yadav <pratyush@kernel.org>
Currently file handlers only get the serialized_data field to store
their state. This field has a pointer to the serialized state of the
file, and it becomes a part of LUO file's serialized state.
File handlers can also need some runtime state to track information that
shouldn't make it in the serialized data.
One such example is a vmalloc pointer. While kho_preserve_vmalloc()
preserves the memory backing a vmalloc allocation, it does not store the
original vmap pointer, since that has no use being passed to the next
kernel. The pointer is needed to free the memory in case the file is
unpreserved.
Provide a private field in struct luo_file and pass it to all the
callbacks. The field's can be set by preserve, and must be freed by
unpreserve.
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
include/linux/liveupdate.h | 5 +++++
kernel/liveupdate/luo_file.c | 9 +++++++++
2 files changed, 14 insertions(+)
diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
index 36a831ae3ead..defc69a1985d 100644
--- a/include/linux/liveupdate.h
+++ b/include/linux/liveupdate.h
@@ -29,6 +29,10 @@ struct file;
* this to the file being operated on.
* @serialized_data: The opaque u64 handle, preserve/prepare/freeze may update
* this field.
+ * @private_data: Private data for the file used to hold runtime state that
+ * is not preserved. Set by the handler's .preserve()
+ * callback, and must be freed in the handler's
+ * .unpreserve() callback.
*
* This structure bundles all parameters for the file operation callbacks.
* The 'data' and 'file' fields are used for both input and output.
@@ -39,6 +43,7 @@ struct liveupdate_file_op_args {
bool retrieved;
struct file *file;
u64 serialized_data;
+ void *private_data;
};
/**
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 3d3bd84cb281..df337c9c4f21 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -126,6 +126,10 @@ static LIST_HEAD(luo_file_handler_list);
* This handle is passed back to the handler's .freeze(),
* .retrieve(), and .finish() callbacks, allowing it to track
* and update its serialized state across phases.
+ * @private_data: Pointer to the private data for the file used to hold runtime
+ * state that is not preserved. Set by the handler's .preserve()
+ * callback, and must be freed in the handler's .unpreserve()
+ * callback.
* @retrieved: A flag indicating whether a user/kernel in the new kernel has
* successfully called retrieve() on this file. This prevents
* multiple retrieval attempts.
@@ -152,6 +156,7 @@ struct luo_file {
struct liveupdate_file_handler *fh;
struct file *file;
u64 serialized_data;
+ void *private_data;
bool retrieved;
struct mutex mutex;
struct list_head list;
@@ -309,6 +314,7 @@ int luo_preserve_file(struct luo_session *session, u64 token, int fd)
goto exit_err;
} else {
luo_file->serialized_data = args.serialized_data;
+ luo_file->private_data = args.private_data;
list_add_tail(&luo_file->list, &session->files_list);
session->count++;
}
@@ -356,6 +362,7 @@ void luo_file_unpreserve_files(struct luo_session *session)
args.session = (struct liveupdate_session *)session;
args.file = luo_file->file;
args.serialized_data = luo_file->serialized_data;
+ args.private_data = luo_file->private_data;
luo_file->fh->ops->unpreserve(&args);
luo_flb_file_unpreserve(luo_file->fh);
@@ -384,6 +391,7 @@ static int luo_file_freeze_one(struct luo_session *session,
args.session = (struct liveupdate_session *)session;
args.file = luo_file->file;
args.serialized_data = luo_file->serialized_data;
+ args.private_data = luo_file->private_data;
err = luo_file->fh->ops->freeze(&args);
if (!err)
@@ -405,6 +413,7 @@ static void luo_file_unfreeze_one(struct luo_session *session,
args.session = (struct liveupdate_session *)session;
args.file = luo_file->file;
args.serialized_data = luo_file->serialized_data;
+ args.private_data = luo_file->private_data;
luo_file->fh->ops->unfreeze(&args);
}
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 15/20] mm: memfd_luo: allow preserving memfd
From: Pasha Tatashin @ 2025-11-15 23:34 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
From: Pratyush Yadav <ptyadav@amazon.de>
The ability to preserve a memfd allows userspace to use KHO and LUO to
transfer its memory contents to the next kernel. This is useful in many
ways. For one, it can be used with IOMMUFD as the backing store for
IOMMU page tables. Preserving IOMMUFD is essential for performing a
hypervisor live update with passthrough devices. memfd support provides
the first building block for making that possible.
For another, applications with a large amount of memory that takes time
to reconstruct, reboots to consume kernel upgrades can be very
expensive. memfd with LUO gives those applications reboot-persistent
memory that they can use to quickly save and reconstruct that state.
While memfd is backed by either hugetlbfs or shmem, currently only
support on shmem is added. To be more precise, support for anonymous
shmem files is added.
The handover to the next kernel is not transparent. All the properties
of the file are not preserved; only its memory contents, position, and
size. The recreated file gets the UID and GID of the task doing the
restore, and the task's cgroup gets charged with the memory.
Once preserved, the file cannot grow or shrink, and all its pages are
pinned to avoid migrations and swapping. The file can still be read from
or written to.
Use vmalloc to get the buffer to hold the folios, and preserve
it using kho_preserve_vmalloc(). This doesn't have the size limit.
Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
---
MAINTAINERS | 2 +
include/linux/liveupdate/abi/memfd.h | 88 ++++
mm/Makefile | 1 +
mm/memfd_luo.c | 671 +++++++++++++++++++++++++++
4 files changed, 762 insertions(+)
create mode 100644 include/linux/liveupdate/abi/memfd.h
create mode 100644 mm/memfd_luo.c
diff --git a/MAINTAINERS b/MAINTAINERS
index bc9f5c6f0e80..ad9fee6dc605 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14466,6 +14466,7 @@ F: tools/testing/selftests/livepatch/
LIVE UPDATE
M: Pasha Tatashin <pasha.tatashin@soleen.com>
+R: Pratyush Yadav <pratyush@kernel.org>
L: linux-kernel@vger.kernel.org
S: Maintained
F: Documentation/core-api/liveupdate.rst
@@ -14474,6 +14475,7 @@ F: include/linux/liveupdate.h
F: include/linux/liveupdate/
F: include/uapi/linux/liveupdate.h
F: kernel/liveupdate/
+F: mm/memfd_luo.c
LLC (802.2)
L: netdev@vger.kernel.org
diff --git a/include/linux/liveupdate/abi/memfd.h b/include/linux/liveupdate/abi/memfd.h
new file mode 100644
index 000000000000..bf848e5bd1de
--- /dev/null
+++ b/include/linux/liveupdate/abi/memfd.h
@@ -0,0 +1,88 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ *
+ * Copyright (C) 2025 Amazon.com Inc. or its affiliates.
+ * Pratyush Yadav <ptyadav@amazon.de>
+ */
+
+#ifndef _LINUX_LIVEUPDATE_ABI_MEMFD_H
+#define _LINUX_LIVEUPDATE_ABI_MEMFD_H
+
+/**
+ * DOC: memfd Live Update ABI
+ *
+ * This header defines the ABI for preserving the state of a memfd across a
+ * kexec reboot using the LUO.
+ *
+ * The state is serialized into a Flattened Device Tree which is then handed
+ * over to the next kernel via the KHO mechanism. The FDT is passed as the
+ * opaque `data` handle in the file handler callbacks.
+ *
+ * This interface is a contract. Any modification to the FDT structure,
+ * node properties, compatible string, or the layout of the serialization
+ * structures defined here constitutes a breaking change. Such changes require
+ * incrementing the version number in the MEMFD_LUO_FH_COMPATIBLE string.
+ *
+ * FDT Structure Overview:
+ * The memfd state is contained within a single FDT with the following layout:
+ *
+ * .. code-block:: none
+ *
+ * / {
+ * pos = <...>;
+ * size = <...>;
+ * nr_folios = <...>;
+ * folios = < ... binary data ... >;
+ * };
+ *
+ * Node Properties:
+ * - pos: u64
+ * The file's current position (f_pos).
+ * - size: u64
+ * The total size of the file in bytes (i_size).
+ * - nr_folios: u64
+ * Number of folios in folios array. Only present when size > 0.
+ * - folios: struct kho_vmalloc
+ * KHO vmalloc preservation for an array of &struct memfd_luo_folio_ser,
+ * one for each preserved folio from the original file's mapping. Only
+ * present when size > 0.
+ */
+
+/**
+ * struct memfd_luo_folio_ser - Serialized state of a single folio.
+ * @foliodesc: A packed 64-bit value containing both the PFN and status flags of
+ * the preserved folio. The upper 52 bits store the PFN, and the
+ * lower 12 bits are reserved for flags (e.g., dirty, uptodate).
+ * @index: The page offset (pgoff_t) of the folio within the original file's
+ * address space. This is used to correctly position the folio
+ * during restoration.
+ *
+ * This structure represents the minimal information required to restore a
+ * single folio in the new kernel. An array of these structs forms the binary
+ * data for the "folios" property in the handover FDT.
+ */
+struct memfd_luo_folio_ser {
+ u64 foliodesc;
+ u64 index;
+};
+
+/* The strings used for memfd KHO FDT sub-tree. */
+
+/* 64-bit pos value for the preserved memfd */
+#define MEMFD_FDT_POS "pos"
+
+/* 64-bit size value of the preserved memfd */
+#define MEMFD_FDT_SIZE "size"
+
+#define MEMFD_FDT_FOLIOS "folios"
+
+/* Number of folios in the folios array. */
+#define MEMFD_FDT_NR_FOLIOS "nr_folios"
+
+/* The compatibility string for memfd file handler */
+#define MEMFD_LUO_FH_COMPATIBLE "memfd-v1"
+
+#endif /* _LINUX_LIVEUPDATE_ABI_MEMFD_H */
diff --git a/mm/Makefile b/mm/Makefile
index 21abb3353550..7738ec416f00 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -100,6 +100,7 @@ obj-$(CONFIG_NUMA) += memory-tiers.o
obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o
obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
obj-$(CONFIG_PAGE_COUNTER) += page_counter.o
+obj-$(CONFIG_LIVEUPDATE) += memfd_luo.o
obj-$(CONFIG_MEMCG_V1) += memcontrol-v1.o
obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o
ifdef CONFIG_SWAP
diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
new file mode 100644
index 000000000000..4c1d16db2cff
--- /dev/null
+++ b/mm/memfd_luo.c
@@ -0,0 +1,671 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ *
+ * Copyright (C) 2025 Amazon.com Inc. or its affiliates.
+ * Pratyush Yadav <ptyadav@amazon.de>
+ */
+
+/**
+ * DOC: Memfd Preservation via LUO
+ *
+ * Overview
+ * ========
+ *
+ * Memory file descriptors (memfd) can be preserved over a kexec using the Live
+ * Update Orchestrator (LUO) file preservation. This allows userspace to
+ * transfer its memory contents to the next kernel after a kexec.
+ *
+ * The preservation is not intended to be transparent. Only select properties of
+ * the file are preserved. All others are reset to default. The preserved
+ * properties are described below.
+ *
+ * .. note::
+ * The LUO API is not stabilized yet, so the preserved properties of a memfd
+ * are also not stable and are subject to backwards incompatible changes.
+ *
+ * .. note::
+ * Currently a memfd backed by Hugetlb is not supported. Memfds created
+ * with ``MFD_HUGETLB`` will be rejected.
+ *
+ * Preserved Properties
+ * ====================
+ *
+ * The following properties of the memfd are preserved across kexec:
+ *
+ * File Contents
+ * All data stored in the file is preserved.
+ *
+ * File Size
+ * The size of the file is preserved. Holes in the file are filled by
+ * allocating pages for them during preservation.
+ *
+ * File Position
+ * The current file position is preserved, allowing applications to continue
+ * reading/writing from their last position.
+ *
+ * File Status Flags
+ * memfds are always opened with ``O_RDWR`` and ``O_LARGEFILE``. This property
+ * is maintained.
+ *
+ * Non-Preserved Properties
+ * ========================
+ *
+ * All properties which are not preserved must be assumed to be reset to
+ * default. This section describes some of those properties which may be more of
+ * note.
+ *
+ * ``FD_CLOEXEC`` flag
+ * A memfd can be created with the ``MFD_CLOEXEC`` flag that sets the
+ * ``FD_CLOEXEC`` on the file. This flag is not preserved and must be set
+ * again after restore via ``fcntl()``.
+ *
+ * Seals
+ * File seals are not preserved. The file is unsealed on restore and if
+ * needed, must be sealed again via ``fcntl()``.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/bits.h>
+#include <linux/err.h>
+#include <linux/file.h>
+#include <linux/io.h>
+#include <linux/kexec_handover.h>
+#include <linux/libfdt.h>
+#include <linux/liveupdate.h>
+#include <linux/liveupdate/abi/memfd.h>
+#include <linux/shmem_fs.h>
+#include <linux/vmalloc.h>
+#include "internal.h"
+
+#define PRESERVED_PFN_MASK GENMASK(63, 12)
+#define PRESERVED_PFN_SHIFT 12
+#define PRESERVED_FLAG_DIRTY BIT(0)
+#define PRESERVED_FLAG_UPTODATE BIT(1)
+
+#define PRESERVED_FOLIO_PFN(desc) (((desc) & PRESERVED_PFN_MASK) >> PRESERVED_PFN_SHIFT)
+#define PRESERVED_FOLIO_FLAGS(desc) ((desc) & ~PRESERVED_PFN_MASK)
+#define PRESERVED_FOLIO_MKDESC(pfn, flags) (((pfn) << PRESERVED_PFN_SHIFT) | (flags))
+
+struct memfd_luo_private {
+ struct memfd_luo_folio_ser *pfolios;
+ u64 nr_folios;
+};
+
+static struct memfd_luo_folio_ser *memfd_luo_preserve_folios(struct file *file, void *fdt,
+ u64 *nr_foliosp)
+{
+ struct inode *inode = file_inode(file);
+ struct memfd_luo_folio_ser *pfolios;
+ struct kho_vmalloc *kho_vmalloc;
+ unsigned int max_folios;
+ long i, size, nr_pinned;
+ struct folio **folios;
+ int err = -EINVAL;
+ pgoff_t offset;
+ u64 nr_folios;
+
+ size = i_size_read(inode);
+ /*
+ * If the file has zero size, then the folios and nr_folios properties
+ * are not set.
+ */
+ if (!size) {
+ *nr_foliosp = 0;
+ return NULL;
+ }
+
+ /*
+ * Guess the number of folios based on inode size. Real number might end
+ * up being smaller if there are higher order folios.
+ */
+ max_folios = PAGE_ALIGN(size) / PAGE_SIZE;
+ folios = kvmalloc_array(max_folios, sizeof(*folios), GFP_KERNEL);
+ if (!folios)
+ return ERR_PTR(-ENOMEM);
+
+ /*
+ * Pin the folios so they don't move around behind our back. This also
+ * ensures none of the folios are in CMA -- which ensures they don't
+ * fall in KHO scratch memory. It also moves swapped out folios back to
+ * memory.
+ *
+ * A side effect of doing this is that it allocates a folio for all
+ * indices in the file. This might waste memory on sparse memfds. If
+ * that is really a problem in the future, we can have a
+ * memfd_pin_folios() variant that does not allocate a page on empty
+ * slots.
+ */
+ nr_pinned = memfd_pin_folios(file, 0, size - 1, folios, max_folios,
+ &offset);
+ if (nr_pinned < 0) {
+ err = nr_pinned;
+ pr_err("failed to pin folios: %d\n", err);
+ goto err_free_folios;
+ }
+ nr_folios = nr_pinned;
+
+ err = fdt_property(fdt, MEMFD_FDT_NR_FOLIOS, &nr_folios, sizeof(nr_folios));
+ if (err)
+ goto err_unpin;
+
+ err = fdt_property_placeholder(fdt, MEMFD_FDT_FOLIOS, sizeof(*kho_vmalloc),
+ (void **)&kho_vmalloc);
+ if (err) {
+ pr_err("Failed to reserve '%s' property in FDT: %s\n",
+ MEMFD_FDT_FOLIOS, fdt_strerror(err));
+ err = -ENOMEM;
+ goto err_unpin;
+ }
+
+ pfolios = vcalloc(nr_folios, sizeof(*pfolios));
+ if (!pfolios) {
+ err = -ENOMEM;
+ goto err_unpin;
+ }
+
+ for (i = 0; i < nr_folios; i++) {
+ struct memfd_luo_folio_ser *pfolio = &pfolios[i];
+ struct folio *folio = folios[i];
+ unsigned int flags = 0;
+ unsigned long pfn;
+
+ err = kho_preserve_folio(folio);
+ if (err)
+ goto err_unpreserve;
+
+ pfn = folio_pfn(folio);
+ if (folio_test_dirty(folio))
+ flags |= PRESERVED_FLAG_DIRTY;
+ if (folio_test_uptodate(folio))
+ flags |= PRESERVED_FLAG_UPTODATE;
+
+ pfolio->foliodesc = PRESERVED_FOLIO_MKDESC(pfn, flags);
+ pfolio->index = folio->index;
+ }
+
+ err = kho_preserve_vmalloc(pfolios, kho_vmalloc);
+ if (err)
+ goto err_unpreserve;
+
+ kvfree(folios);
+ *nr_foliosp = nr_folios;
+ return pfolios;
+
+err_unpreserve:
+ i--;
+ for (; i >= 0; i--)
+ kho_unpreserve_folio(folios[i]);
+ vfree(pfolios);
+err_unpin:
+ unpin_folios(folios, nr_folios);
+err_free_folios:
+ kvfree(folios);
+ return ERR_PTR(err);
+}
+
+static void memfd_luo_unpreserve_folios(void *fdt, struct memfd_luo_folio_ser *pfolios,
+ u64 nr_folios)
+{
+ struct kho_vmalloc *kho_vmalloc;
+ long i;
+
+ if (!nr_folios)
+ return;
+
+ kho_vmalloc = (struct kho_vmalloc *)fdt_getprop(fdt, 0, MEMFD_FDT_FOLIOS, NULL);
+ /* The FDT was created by this kernel so expect it to be sane. */
+ WARN_ON_ONCE(!kho_vmalloc);
+ kho_unpreserve_vmalloc(kho_vmalloc);
+
+ for (i = 0; i < nr_folios; i++) {
+ const struct memfd_luo_folio_ser *pfolio = &pfolios[i];
+ struct folio *folio;
+
+ if (!pfolio->foliodesc)
+ continue;
+
+ folio = pfn_folio(PRESERVED_FOLIO_PFN(pfolio->foliodesc));
+
+ kho_unpreserve_folio(folio);
+ unpin_folio(folio);
+ }
+
+ vfree(pfolios);
+}
+
+static struct memfd_luo_folio_ser *memfd_luo_fdt_folios(const void *fdt, u64 *nr_folios)
+{
+ const struct kho_vmalloc *kho_vmalloc;
+ struct memfd_luo_folio_ser *pfolios;
+ const u64 *nr;
+ int len;
+
+ nr = fdt_getprop(fdt, 0, MEMFD_FDT_NR_FOLIOS, &len);
+ if (!nr || len != sizeof(*nr)) {
+ pr_err("invalid '%s' property\n", MEMFD_FDT_NR_FOLIOS);
+ return NULL;
+ }
+
+ kho_vmalloc = fdt_getprop(fdt, 0, MEMFD_FDT_FOLIOS, &len);
+ if (!kho_vmalloc || len != sizeof(*kho_vmalloc)) {
+ pr_err("invalid '%s' property\n", MEMFD_FDT_FOLIOS);
+ return NULL;
+ }
+
+ pfolios = kho_restore_vmalloc(kho_vmalloc);
+ if (!pfolios)
+ return NULL;
+
+ *nr_folios = *nr;
+ return pfolios;
+}
+
+static void *memfd_luo_create_fdt(void)
+{
+ struct folio *fdt_folio;
+ int err = 0;
+ void *fdt;
+
+ /*
+ * The FDT only contains a couple of properties and a kho_vmalloc
+ * object. One page should be enough for that.
+ */
+ fdt_folio = folio_alloc(GFP_KERNEL | __GFP_ZERO, 0);
+ if (!fdt_folio)
+ return NULL;
+
+ fdt = folio_address(fdt_folio);
+
+ err |= fdt_create(fdt, folio_size(fdt_folio));
+ err |= fdt_finish_reservemap(fdt);
+ err |= fdt_begin_node(fdt, "");
+ if (err)
+ goto free;
+
+ return fdt;
+
+free:
+ folio_put(fdt_folio);
+ return NULL;
+}
+
+static int memfd_luo_finish_fdt(void *fdt)
+{
+ int err;
+
+ err = fdt_end_node(fdt);
+ if (err)
+ return err;
+
+ return fdt_finish(fdt);
+}
+
+static int memfd_luo_preserve(struct liveupdate_file_op_args *args)
+{
+ struct inode *inode = file_inode(args->file);
+ struct memfd_luo_folio_ser *pfolios;
+ struct memfd_luo_private *private;
+ u64 pos, nr_folios;
+ int err = 0;
+ void *fdt;
+ long size;
+
+ private = kmalloc(sizeof(*private), GFP_KERNEL);
+ if (!private)
+ return -ENOMEM;
+
+ inode_lock(inode);
+ shmem_i_mapping_freeze(inode, true);
+
+ size = i_size_read(inode);
+
+ fdt = memfd_luo_create_fdt();
+ if (!fdt) {
+ err = -ENOMEM;
+ goto err_unlock;
+ }
+
+ pos = args->file->f_pos;
+ err = fdt_property(fdt, MEMFD_FDT_POS, &pos, sizeof(pos));
+ if (err)
+ goto err_free_fdt;
+
+ err = fdt_property(fdt, MEMFD_FDT_SIZE, &size, sizeof(size));
+ if (err)
+ goto err_free_fdt;
+
+ pfolios = memfd_luo_preserve_folios(args->file, fdt, &nr_folios);
+ if (IS_ERR(pfolios)) {
+ err = PTR_ERR(pfolios);
+ goto err_free_fdt;
+ }
+
+ err = memfd_luo_finish_fdt(fdt);
+ if (err)
+ goto err_unpreserve_folios;
+
+ err = kho_preserve_folio(virt_to_folio(fdt));
+ if (err)
+ goto err_unpreserve_folios;
+
+ inode_unlock(inode);
+
+ private->pfolios = pfolios;
+ private->nr_folios = nr_folios;
+ args->private_data = private;
+ args->serialized_data = virt_to_phys(fdt);
+ return 0;
+
+err_unpreserve_folios:
+ memfd_luo_unpreserve_folios(fdt, pfolios, nr_folios);
+err_free_fdt:
+ folio_put(virt_to_folio(fdt));
+err_unlock:
+ shmem_i_mapping_freeze(inode, false);
+ inode_unlock(inode);
+ kfree(private);
+ return err;
+}
+
+static int memfd_luo_freeze(struct liveupdate_file_op_args *args)
+{
+ u64 pos = args->file->f_pos;
+ void *fdt;
+ int err;
+
+ if (WARN_ON_ONCE(!args->serialized_data))
+ return -EINVAL;
+
+ fdt = phys_to_virt(args->serialized_data);
+
+ /*
+ * The pos might have changed since prepare. Everything else stays the
+ * same.
+ */
+ err = fdt_setprop(fdt, 0, "pos", &pos, sizeof(pos));
+ if (err)
+ return err;
+
+ return 0;
+}
+
+static void memfd_luo_unpreserve(struct liveupdate_file_op_args *args)
+{
+ struct memfd_luo_private *private = args->private_data;
+ struct inode *inode = file_inode(args->file);
+ struct folio *fdt_folio;
+ void *fdt;
+
+ if (WARN_ON_ONCE(!args->serialized_data || !args->private_data))
+ return;
+
+ inode_lock(inode);
+ shmem_i_mapping_freeze(inode, false);
+
+ fdt = phys_to_virt(args->serialized_data);
+ fdt_folio = virt_to_folio(fdt);
+
+ memfd_luo_unpreserve_folios(fdt, private->pfolios, private->nr_folios);
+
+ kho_unpreserve_folio(fdt_folio);
+ folio_put(fdt_folio);
+ inode_unlock(inode);
+ kfree(private);
+}
+
+static struct folio *memfd_luo_get_fdt(u64 data)
+{
+ return kho_restore_folio((phys_addr_t)data);
+}
+
+static void memfd_luo_discard_folios(const struct memfd_luo_folio_ser *pfolios,
+ long nr_folios)
+{
+ unsigned int i;
+
+ for (i = 0; i < nr_folios; i++) {
+ const struct memfd_luo_folio_ser *pfolio = &pfolios[i];
+ struct folio *folio;
+ phys_addr_t phys;
+
+ if (!pfolio->foliodesc)
+ continue;
+
+ phys = PFN_PHYS(PRESERVED_FOLIO_PFN(pfolio->foliodesc));
+ folio = kho_restore_folio(phys);
+ if (!folio) {
+ pr_warn_ratelimited("Unable to restore folio at physical address: %llx\n",
+ phys);
+ continue;
+ }
+
+ folio_put(folio);
+ }
+}
+
+static void memfd_luo_finish(struct liveupdate_file_op_args *args)
+{
+ const struct memfd_luo_folio_ser *pfolios;
+ struct folio *fdt_folio;
+ const void *fdt;
+ u64 nr_folios;
+
+ if (args->retrieved)
+ return;
+
+ fdt_folio = memfd_luo_get_fdt(args->serialized_data);
+ if (!fdt_folio) {
+ pr_err("failed to restore memfd FDT\n");
+ return;
+ }
+
+ fdt = folio_address(fdt_folio);
+
+ pfolios = memfd_luo_fdt_folios(fdt, &nr_folios);
+ if (!pfolios)
+ goto out;
+
+ memfd_luo_discard_folios(pfolios, nr_folios);
+ vfree(pfolios);
+
+out:
+ folio_put(fdt_folio);
+}
+
+static int memfd_luo_retrieve_folios(struct file *file, const void *fdt)
+{
+ const struct memfd_luo_folio_ser *pfolios;
+ struct inode *inode = file_inode(file);
+ struct address_space *mapping;
+ struct folio *folio;
+ u64 nr_folios;
+ long i = 0;
+ int err;
+
+ /* Careful: folios don't exist in FDT on zero-size files. */
+ if (!inode->i_size)
+ return 0;
+
+ pfolios = memfd_luo_fdt_folios(fdt, &nr_folios);
+ if (!pfolios) {
+ pr_err("failed to fetch preserved folio list\n");
+ return -EINVAL;
+ }
+
+ inode = file->f_inode;
+ mapping = inode->i_mapping;
+
+ for (; i < nr_folios; i++) {
+ const struct memfd_luo_folio_ser *pfolio = &pfolios[i];
+ phys_addr_t phys;
+ u64 index;
+ int flags;
+
+ if (!pfolio->foliodesc)
+ continue;
+
+ phys = PFN_PHYS(PRESERVED_FOLIO_PFN(pfolio->foliodesc));
+ folio = kho_restore_folio(phys);
+ if (!folio) {
+ pr_err("Unable to restore folio at physical address: %llx\n",
+ phys);
+ goto put_folios;
+ }
+ index = pfolio->index;
+ flags = PRESERVED_FOLIO_FLAGS(pfolio->foliodesc);
+
+ /* Set up the folio for insertion. */
+ __folio_set_locked(folio);
+ __folio_set_swapbacked(folio);
+
+ err = mem_cgroup_charge(folio, NULL, mapping_gfp_mask(mapping));
+ if (err) {
+ pr_err("shmem: failed to charge folio index %ld: %d\n",
+ i, err);
+ goto unlock_folio;
+ }
+
+ err = shmem_add_to_page_cache(folio, mapping, index, NULL,
+ mapping_gfp_mask(mapping));
+ if (err) {
+ pr_err("shmem: failed to add to page cache folio index %ld: %d\n",
+ i, err);
+ goto unlock_folio;
+ }
+
+ if (flags & PRESERVED_FLAG_UPTODATE)
+ folio_mark_uptodate(folio);
+ if (flags & PRESERVED_FLAG_DIRTY)
+ folio_mark_dirty(folio);
+
+ err = shmem_inode_acct_blocks(inode, 1);
+ if (err) {
+ pr_err("shmem: failed to account folio index %ld: %d\n",
+ i, err);
+ goto unlock_folio;
+ }
+
+ shmem_recalc_inode(inode, 1, 0);
+ folio_add_lru(folio);
+ folio_unlock(folio);
+ folio_put(folio);
+ }
+
+ vfree(pfolios);
+ return 0;
+
+unlock_folio:
+ folio_unlock(folio);
+ folio_put(folio);
+ i++;
+put_folios:
+ /*
+ * Note: don't free the folios already added to the file. They will be
+ * freed when the file is freed. Free the ones not added yet here.
+ */
+ for (; i < nr_folios; i++) {
+ const struct memfd_luo_folio_ser *pfolio = &pfolios[i];
+
+ folio = kho_restore_folio(PRESERVED_FOLIO_PFN(pfolio->foliodesc));
+ if (folio)
+ folio_put(folio);
+ }
+
+ vfree(pfolios);
+ return err;
+}
+
+static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
+{
+ struct folio *fdt_folio;
+ const u64 *pos, *size;
+ struct file *file;
+ int len, ret = 0;
+ const void *fdt;
+
+ fdt_folio = memfd_luo_get_fdt(args->serialized_data);
+ if (!fdt_folio)
+ return -ENOENT;
+
+ fdt = page_to_virt(folio_page(fdt_folio, 0));
+
+ size = fdt_getprop(fdt, 0, "size", &len);
+ if (!size || len != sizeof(u64)) {
+ pr_err("invalid 'size' property\n");
+ ret = -EINVAL;
+ goto put_fdt;
+ }
+
+ pos = fdt_getprop(fdt, 0, "pos", &len);
+ if (!pos || len != sizeof(u64)) {
+ pr_err("invalid 'pos' property\n");
+ ret = -EINVAL;
+ goto put_fdt;
+ }
+
+ file = shmem_file_setup("", 0, VM_NORESERVE);
+
+ if (IS_ERR(file)) {
+ ret = PTR_ERR(file);
+ pr_err("failed to setup file: %d\n", ret);
+ goto put_fdt;
+ }
+
+ vfs_setpos(file, *pos, MAX_LFS_FILESIZE);
+ file->f_inode->i_size = *size;
+
+ ret = memfd_luo_retrieve_folios(file, fdt);
+ if (ret)
+ goto put_file;
+
+ args->file = file;
+ folio_put(fdt_folio);
+ return 0;
+
+put_file:
+ fput(file);
+put_fdt:
+ folio_put(fdt_folio);
+ return ret;
+}
+
+static bool memfd_luo_can_preserve(struct liveupdate_file_handler *handler,
+ struct file *file)
+{
+ struct inode *inode = file_inode(file);
+
+ return shmem_file(file) && !inode->i_nlink;
+}
+
+static const struct liveupdate_file_ops memfd_luo_file_ops = {
+ .freeze = memfd_luo_freeze,
+ .finish = memfd_luo_finish,
+ .retrieve = memfd_luo_retrieve,
+ .preserve = memfd_luo_preserve,
+ .unpreserve = memfd_luo_unpreserve,
+ .can_preserve = memfd_luo_can_preserve,
+ .owner = THIS_MODULE,
+};
+
+static struct liveupdate_file_handler memfd_luo_handler = {
+ .ops = &memfd_luo_file_ops,
+ .compatible = MEMFD_LUO_FH_COMPATIBLE,
+};
+
+static int __init memfd_luo_init(void)
+{
+ int err = liveupdate_register_file_handler(&memfd_luo_handler);
+
+ if (err && err != -EOPNOTSUPP) {
+ pr_err("Could not register luo filesystem handler: %pe\n", ERR_PTR(err));
+
+ return err;
+ }
+
+ return 0;
+}
+late_initcall(memfd_luo_init);
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 16/20] docs: add documentation for memfd preservation via LUO
From: Pasha Tatashin @ 2025-11-15 23:34 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
From: Pratyush Yadav <ptyadav@amazon.de>
Add the documentation under the "Preserving file descriptors" section of
LUO's documentation.
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
Co-developed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
Documentation/core-api/liveupdate.rst | 7 +++++++
Documentation/mm/index.rst | 1 +
Documentation/mm/memfd_preservation.rst | 23 +++++++++++++++++++++++
MAINTAINERS | 1 +
4 files changed, 32 insertions(+)
create mode 100644 Documentation/mm/memfd_preservation.rst
diff --git a/Documentation/core-api/liveupdate.rst b/Documentation/core-api/liveupdate.rst
index deacc098d024..384de79a2457 100644
--- a/Documentation/core-api/liveupdate.rst
+++ b/Documentation/core-api/liveupdate.rst
@@ -28,6 +28,13 @@ Live Update Orchestrator ABI
.. kernel-doc:: include/linux/liveupdate/abi/luo.h
:doc: Live Update Orchestrator ABI
+The following types of file descriptors can be preserved
+
+.. toctree::
+ :maxdepth: 1
+
+ ../mm/memfd_preservation
+
Public API
==========
.. kernel-doc:: include/linux/liveupdate.h
diff --git a/Documentation/mm/index.rst b/Documentation/mm/index.rst
index ba6a8872849b..7aa2a8886908 100644
--- a/Documentation/mm/index.rst
+++ b/Documentation/mm/index.rst
@@ -48,6 +48,7 @@ documentation, or deleted if it has served its purpose.
hugetlbfs_reserv
ksm
memory-model
+ memfd_preservation
mmu_notifier
multigen_lru
numa
diff --git a/Documentation/mm/memfd_preservation.rst b/Documentation/mm/memfd_preservation.rst
new file mode 100644
index 000000000000..4f09c3921893
--- /dev/null
+++ b/Documentation/mm/memfd_preservation.rst
@@ -0,0 +1,23 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+==========================
+Memfd Preservation via LUO
+==========================
+
+.. kernel-doc:: mm/memfd_luo.c
+ :doc: Memfd Preservation via LUO
+
+Memfd Preservation ABI
+======================
+
+.. kernel-doc:: include/linux/liveupdate/abi/memfd.h
+ :doc: DOC: memfd Live Update ABI
+
+.. kernel-doc:: include/linux/liveupdate/abi/memfd.h
+ :internal:
+
+See Also
+========
+
+- :doc:`/core-api/liveupdate`
+- :doc:`/core-api/kho/concepts`
diff --git a/MAINTAINERS b/MAINTAINERS
index ad9fee6dc605..6ffe4425adbf 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14470,6 +14470,7 @@ R: Pratyush Yadav <pratyush@kernel.org>
L: linux-kernel@vger.kernel.org
S: Maintained
F: Documentation/core-api/liveupdate.rst
+F: Documentation/mm/memfd_preservation.rst
F: Documentation/userspace-api/liveupdate.rst
F: include/linux/liveupdate.h
F: include/linux/liveupdate/
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 17/20] selftests/liveupdate: Add userspace API selftests
From: Pasha Tatashin @ 2025-11-15 23:34 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
Introduce a selftest suite for LUO. These tests validate the core
userspace-facing API provided by the /dev/liveupdate device and its
associated ioctls.
The suite covers fundamental device behavior, session management, and
the file preservation mechanism using memfd as a test case. This
provides regression testing for the LUO uAPI.
The following functionality is verified:
Device Access:
Basic open and close operations on /dev/liveupdate.
Enforcement of exclusive device access (verifying EBUSY on a
second open).
Session Management:
Successful creation of sessions with unique names.
Failure to create sessions with duplicate names.
File Preservation:
Preserving a single memfd and verifying its content remains
intact post-preservation.
Preserving multiple memfds within a single session, each with
unique data.
A complex scenario involving multiple sessions, each containing
a mix of empty and data-filled memfds.
Note: This test suite is limited to verifying the pre-kexec
functionality of LUO (e.g., session creation, file preservation).
The post-kexec restoration of resources is not covered, as the kselftest
framework does not currently support orchestrating a reboot and
continuing execution in the new kernel.
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
MAINTAINERS | 1 +
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/liveupdate/.gitignore | 1 +
tools/testing/selftests/liveupdate/Makefile | 7 +
tools/testing/selftests/liveupdate/config | 5 +
.../testing/selftests/liveupdate/liveupdate.c | 348 ++++++++++++++++++
6 files changed, 363 insertions(+)
create mode 100644 tools/testing/selftests/liveupdate/.gitignore
create mode 100644 tools/testing/selftests/liveupdate/Makefile
create mode 100644 tools/testing/selftests/liveupdate/config
create mode 100644 tools/testing/selftests/liveupdate/liveupdate.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 6ffe4425adbf..5a1ed783de20 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14477,6 +14477,7 @@ F: include/linux/liveupdate/
F: include/uapi/linux/liveupdate.h
F: kernel/liveupdate/
F: mm/memfd_luo.c
+F: tools/testing/selftests/liveupdate/
LLC (802.2)
L: netdev@vger.kernel.org
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index c46ebdb9b8ef..56e44a98d6a5 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -54,6 +54,7 @@ TARGETS += kvm
TARGETS += landlock
TARGETS += lib
TARGETS += livepatch
+TARGETS += liveupdate
TARGETS += lkdtm
TARGETS += lsm
TARGETS += membarrier
diff --git a/tools/testing/selftests/liveupdate/.gitignore b/tools/testing/selftests/liveupdate/.gitignore
new file mode 100644
index 000000000000..af6e773cf98f
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/.gitignore
@@ -0,0 +1 @@
+/liveupdate
diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
new file mode 100644
index 000000000000..2a573c36016e
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-only
+CFLAGS += -Wall -O2 -Wno-unused-function
+CFLAGS += $(KHDR_INCLUDES)
+
+TEST_GEN_PROGS += liveupdate
+
+include ../lib.mk
diff --git a/tools/testing/selftests/liveupdate/config b/tools/testing/selftests/liveupdate/config
new file mode 100644
index 000000000000..c0c7e7cc484e
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/config
@@ -0,0 +1,5 @@
+CONFIG_KEXEC_FILE=y
+CONFIG_KEXEC_HANDOVER=y
+CONFIG_KEXEC_HANDOVER_DEBUGFS=y
+CONFIG_KEXEC_HANDOVER_DEBUG=y
+CONFIG_LIVEUPDATE=y
diff --git a/tools/testing/selftests/liveupdate/liveupdate.c b/tools/testing/selftests/liveupdate/liveupdate.c
new file mode 100644
index 000000000000..c2878e3d5ef9
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/liveupdate.c
@@ -0,0 +1,348 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+
+/*
+ * Selftests for the Live Update Orchestrator.
+ * This test suite verifies the functionality and behavior of the
+ * /dev/liveupdate character device and its session management capabilities.
+ *
+ * Tests include:
+ * - Device access: basic open/close, and enforcement of exclusive access.
+ * - Session management: creation of unique sessions, and duplicate name detection.
+ * - Resource preservation: successfully preserving individual and multiple memfds,
+ * verifying contents remain accessible.
+ * - Complex multi-session scenarios involving mixed empty and populated files.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include <linux/liveupdate.h>
+
+#include "../kselftest.h"
+#include "../kselftest_harness.h"
+
+#define LIVEUPDATE_DEV "/dev/liveupdate"
+
+FIXTURE(liveupdate_device) {
+ int fd1;
+ int fd2;
+};
+
+FIXTURE_SETUP(liveupdate_device)
+{
+ self->fd1 = -1;
+ self->fd2 = -1;
+}
+
+FIXTURE_TEARDOWN(liveupdate_device)
+{
+ if (self->fd1 >= 0)
+ close(self->fd1);
+ if (self->fd2 >= 0)
+ close(self->fd2);
+}
+
+/*
+ * Test Case: Basic Open and Close
+ *
+ * Verifies that the /dev/liveupdate device can be opened and subsequently
+ * closed without errors. Skips if the device does not exist.
+ */
+TEST_F(liveupdate_device, basic_open_close)
+{
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist.", LIVEUPDATE_DEV);
+
+ ASSERT_GE(self->fd1, 0);
+ ASSERT_EQ(close(self->fd1), 0);
+ self->fd1 = -1;
+}
+
+/*
+ * Test Case: Exclusive Open Enforcement
+ *
+ * Verifies that the /dev/liveupdate device can only be opened by one process
+ * at a time. It checks that a second attempt to open the device fails with
+ * the EBUSY error code.
+ */
+TEST_F(liveupdate_device, exclusive_open)
+{
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist.", LIVEUPDATE_DEV);
+
+ ASSERT_GE(self->fd1, 0);
+ self->fd2 = open(LIVEUPDATE_DEV, O_RDWR);
+ EXPECT_LT(self->fd2, 0);
+ EXPECT_EQ(errno, EBUSY);
+}
+
+/* Helper function to create a LUO session via ioctl. */
+static int create_session(int lu_fd, const char *name)
+{
+ struct liveupdate_ioctl_create_session args = {};
+
+ args.size = sizeof(args);
+ strncpy((char *)args.name, name, sizeof(args.name) - 1);
+
+ if (ioctl(lu_fd, LIVEUPDATE_IOCTL_CREATE_SESSION, &args))
+ return -errno;
+
+ return args.fd;
+}
+
+/*
+ * Test Case: Create Duplicate Session
+ *
+ * Verifies that attempting to create two sessions with the same name fails
+ * on the second attempt with EEXIST.
+ */
+TEST_F(liveupdate_device, create_duplicate_session)
+{
+ int session_fd1, session_fd2;
+
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+
+ ASSERT_GE(self->fd1, 0);
+
+ session_fd1 = create_session(self->fd1, "duplicate-session-test");
+ ASSERT_GE(session_fd1, 0);
+
+ session_fd2 = create_session(self->fd1, "duplicate-session-test");
+ EXPECT_LT(session_fd2, 0);
+ EXPECT_EQ(-session_fd2, EEXIST);
+
+ ASSERT_EQ(close(session_fd1), 0);
+}
+
+/*
+ * Test Case: Create Distinct Sessions
+ *
+ * Verifies that creating two sessions with different names succeeds.
+ */
+TEST_F(liveupdate_device, create_distinct_sessions)
+{
+ int session_fd1, session_fd2;
+
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+
+ ASSERT_GE(self->fd1, 0);
+
+ session_fd1 = create_session(self->fd1, "distinct-session-1");
+ ASSERT_GE(session_fd1, 0);
+
+ session_fd2 = create_session(self->fd1, "distinct-session-2");
+ ASSERT_GE(session_fd2, 0);
+
+ ASSERT_EQ(close(session_fd1), 0);
+ ASSERT_EQ(close(session_fd2), 0);
+}
+
+static int preserve_fd(int session_fd, int fd_to_preserve, __u64 token)
+{
+ struct liveupdate_session_preserve_fd args = {};
+
+ args.size = sizeof(args);
+ args.fd = fd_to_preserve;
+ args.token = token;
+
+ if (ioctl(session_fd, LIVEUPDATE_SESSION_PRESERVE_FD, &args))
+ return -errno;
+
+ return 0;
+}
+
+/*
+ * Test Case: Preserve MemFD
+ *
+ * Verifies that a valid memfd can be successfully preserved in a session and
+ * that its contents remain intact after the preservation call.
+ */
+TEST_F(liveupdate_device, preserve_memfd)
+{
+ const char *test_str = "hello liveupdate";
+ char read_buf[64] = {};
+ int session_fd, mem_fd;
+
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+ ASSERT_GE(self->fd1, 0);
+
+ session_fd = create_session(self->fd1, "preserve-memfd-test");
+ ASSERT_GE(session_fd, 0);
+
+ mem_fd = memfd_create("test-memfd", 0);
+ ASSERT_GE(mem_fd, 0);
+
+ ASSERT_EQ(write(mem_fd, test_str, strlen(test_str)), strlen(test_str));
+ ASSERT_EQ(preserve_fd(session_fd, mem_fd, 0x1234), 0);
+ ASSERT_EQ(close(session_fd), 0);
+
+ ASSERT_EQ(lseek(mem_fd, 0, SEEK_SET), 0);
+ ASSERT_EQ(read(mem_fd, read_buf, sizeof(read_buf)), strlen(test_str));
+ ASSERT_STREQ(read_buf, test_str);
+ ASSERT_EQ(close(mem_fd), 0);
+}
+
+/*
+ * Test Case: Preserve Multiple MemFDs
+ *
+ * Verifies that multiple memfds can be preserved in a single session,
+ * each with a unique token, and that their contents remain distinct and
+ * correct after preservation.
+ */
+TEST_F(liveupdate_device, preserve_multiple_memfds)
+{
+ const char *test_str1 = "data for memfd one";
+ const char *test_str2 = "data for memfd two";
+ char read_buf[64] = {};
+ int session_fd, mem_fd1, mem_fd2;
+
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+ ASSERT_GE(self->fd1, 0);
+
+ session_fd = create_session(self->fd1, "preserve-multi-memfd-test");
+ ASSERT_GE(session_fd, 0);
+
+ mem_fd1 = memfd_create("test-memfd-1", 0);
+ ASSERT_GE(mem_fd1, 0);
+ mem_fd2 = memfd_create("test-memfd-2", 0);
+ ASSERT_GE(mem_fd2, 0);
+
+ ASSERT_EQ(write(mem_fd1, test_str1, strlen(test_str1)), strlen(test_str1));
+ ASSERT_EQ(write(mem_fd2, test_str2, strlen(test_str2)), strlen(test_str2));
+
+ ASSERT_EQ(preserve_fd(session_fd, mem_fd1, 0xAAAA), 0);
+ ASSERT_EQ(preserve_fd(session_fd, mem_fd2, 0xBBBB), 0);
+
+ memset(read_buf, 0, sizeof(read_buf));
+ ASSERT_EQ(lseek(mem_fd1, 0, SEEK_SET), 0);
+ ASSERT_EQ(read(mem_fd1, read_buf, sizeof(read_buf)), strlen(test_str1));
+ ASSERT_STREQ(read_buf, test_str1);
+
+ memset(read_buf, 0, sizeof(read_buf));
+ ASSERT_EQ(lseek(mem_fd2, 0, SEEK_SET), 0);
+ ASSERT_EQ(read(mem_fd2, read_buf, sizeof(read_buf)), strlen(test_str2));
+ ASSERT_STREQ(read_buf, test_str2);
+
+ ASSERT_EQ(close(mem_fd1), 0);
+ ASSERT_EQ(close(mem_fd2), 0);
+ ASSERT_EQ(close(session_fd), 0);
+}
+
+/*
+ * Test Case: Preserve Complex Scenario
+ *
+ * Verifies a more complex scenario with multiple sessions and a mix of empty
+ * and non-empty memfds distributed across them.
+ */
+TEST_F(liveupdate_device, preserve_complex_scenario)
+{
+ const char *data1 = "data for session 1";
+ const char *data2 = "data for session 2";
+ char read_buf[64] = {};
+ int session_fd1, session_fd2;
+ int mem_fd_data1, mem_fd_empty1, mem_fd_data2, mem_fd_empty2;
+
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+ ASSERT_GE(self->fd1, 0);
+
+ session_fd1 = create_session(self->fd1, "complex-session-1");
+ ASSERT_GE(session_fd1, 0);
+ session_fd2 = create_session(self->fd1, "complex-session-2");
+ ASSERT_GE(session_fd2, 0);
+
+ mem_fd_data1 = memfd_create("data1", 0);
+ ASSERT_GE(mem_fd_data1, 0);
+ ASSERT_EQ(write(mem_fd_data1, data1, strlen(data1)), strlen(data1));
+
+ mem_fd_empty1 = memfd_create("empty1", 0);
+ ASSERT_GE(mem_fd_empty1, 0);
+
+ mem_fd_data2 = memfd_create("data2", 0);
+ ASSERT_GE(mem_fd_data2, 0);
+ ASSERT_EQ(write(mem_fd_data2, data2, strlen(data2)), strlen(data2));
+
+ mem_fd_empty2 = memfd_create("empty2", 0);
+ ASSERT_GE(mem_fd_empty2, 0);
+
+ ASSERT_EQ(preserve_fd(session_fd1, mem_fd_data1, 0x1111), 0);
+ ASSERT_EQ(preserve_fd(session_fd1, mem_fd_empty1, 0x2222), 0);
+ ASSERT_EQ(preserve_fd(session_fd2, mem_fd_data2, 0x3333), 0);
+ ASSERT_EQ(preserve_fd(session_fd2, mem_fd_empty2, 0x4444), 0);
+
+ ASSERT_EQ(lseek(mem_fd_data1, 0, SEEK_SET), 0);
+ ASSERT_EQ(read(mem_fd_data1, read_buf, sizeof(read_buf)), strlen(data1));
+ ASSERT_STREQ(read_buf, data1);
+
+ memset(read_buf, 0, sizeof(read_buf));
+ ASSERT_EQ(lseek(mem_fd_data2, 0, SEEK_SET), 0);
+ ASSERT_EQ(read(mem_fd_data2, read_buf, sizeof(read_buf)), strlen(data2));
+ ASSERT_STREQ(read_buf, data2);
+
+ ASSERT_EQ(lseek(mem_fd_empty1, 0, SEEK_SET), 0);
+ ASSERT_EQ(read(mem_fd_empty1, read_buf, sizeof(read_buf)), 0);
+
+ ASSERT_EQ(lseek(mem_fd_empty2, 0, SEEK_SET), 0);
+ ASSERT_EQ(read(mem_fd_empty2, read_buf, sizeof(read_buf)), 0);
+
+ ASSERT_EQ(close(mem_fd_data1), 0);
+ ASSERT_EQ(close(mem_fd_empty1), 0);
+ ASSERT_EQ(close(mem_fd_data2), 0);
+ ASSERT_EQ(close(mem_fd_empty2), 0);
+ ASSERT_EQ(close(session_fd1), 0);
+ ASSERT_EQ(close(session_fd2), 0);
+}
+
+/*
+ * Test Case: Preserve Unsupported File Descriptor
+ *
+ * Verifies that attempting to preserve a file descriptor that does not have
+ * a registered Live Update handler fails gracefully.
+ * Uses /dev/null as a representative of a file type (character device)
+ * that is not supported by the orchestrator.
+ */
+TEST_F(liveupdate_device, preserve_unsupported_fd)
+{
+ int session_fd, unsupported_fd;
+ int ret;
+
+ self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+ if (self->fd1 < 0 && errno == ENOENT)
+ SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+ ASSERT_GE(self->fd1, 0);
+
+ session_fd = create_session(self->fd1, "unsupported-fd-test");
+ ASSERT_GE(session_fd, 0);
+
+ unsupported_fd = open("/dev/null", O_RDWR);
+ ASSERT_GE(unsupported_fd, 0);
+
+ ret = preserve_fd(session_fd, unsupported_fd, 0xDEAD);
+ EXPECT_EQ(ret, -ENOENT);
+
+ ASSERT_EQ(close(unsupported_fd), 0);
+ ASSERT_EQ(close(session_fd), 0);
+}
+
+TEST_HARNESS_MAIN
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 18/20] selftests/liveupdate: Add kexec-based selftest for session lifecycle
From: Pasha Tatashin @ 2025-11-15 23:34 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
Introduce a kexec-based selftest, luo_kexec_simple, to validate the
end-to-end lifecycle of a Live Update Orchestrator (LUO) session across
a reboot.
While existing tests verify the uAPI in a pre-reboot context, this test
ensures that the core functionality—preserving state via Kexec Handover
and restoring it in a new kernel—works as expected.
The test operates in two stages, managing its state across the reboot by
preserving a dedicated "state session" containing a memfd. This
mechanism dogfoods the LUO feature itself for state tracking, making the
test self-contained.
The test validates the following sequence:
Stage 1 (Pre-kexec):
- Creates a test session (test-session).
- Creates and preserves a memfd with a known data pattern into the test
session.
- Creates the state-tracking session to signal progression to Stage 2.
- Executes a kexec reboot via a helper script.
Stage 2 (Post-kexec):
- Retrieves the state-tracking session to confirm it is in the
post-reboot stage.
- Retrieves the preserved test session.
- Restores the memfd from the test session and verifies its contents
match the original data pattern written in Stage 1.
- Finalizes both the test and state sessions to ensure a clean
teardown.
The test relies on a helper script (do_kexec.sh) to perform the reboot
and a shared utility library (luo_test_utils.c) for common LUO
operations, keeping the main test logic clean and focused.
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
tools/testing/selftests/liveupdate/.gitignore | 1 +
tools/testing/selftests/liveupdate/Makefile | 32 ++++
.../testing/selftests/liveupdate/do_kexec.sh | 16 ++
.../selftests/liveupdate/luo_kexec_simple.c | 114 ++++++++++++
.../selftests/liveupdate/luo_test_utils.c | 168 ++++++++++++++++++
.../selftests/liveupdate/luo_test_utils.h | 39 ++++
6 files changed, 370 insertions(+)
create mode 100755 tools/testing/selftests/liveupdate/do_kexec.sh
create mode 100644 tools/testing/selftests/liveupdate/luo_kexec_simple.c
create mode 100644 tools/testing/selftests/liveupdate/luo_test_utils.c
create mode 100644 tools/testing/selftests/liveupdate/luo_test_utils.h
diff --git a/tools/testing/selftests/liveupdate/.gitignore b/tools/testing/selftests/liveupdate/.gitignore
index af6e773cf98f..daeef116174d 100644
--- a/tools/testing/selftests/liveupdate/.gitignore
+++ b/tools/testing/selftests/liveupdate/.gitignore
@@ -1 +1,2 @@
/liveupdate
+/luo_kexec_simple
diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
index 2a573c36016e..1563ac84006a 100644
--- a/tools/testing/selftests/liveupdate/Makefile
+++ b/tools/testing/selftests/liveupdate/Makefile
@@ -1,7 +1,39 @@
# SPDX-License-Identifier: GPL-2.0-only
+
+KHDR_INCLUDES ?= -I../../../../usr/include
CFLAGS += -Wall -O2 -Wno-unused-function
CFLAGS += $(KHDR_INCLUDES)
+LDFLAGS += -static
+OUTPUT ?= .
+
+# --- Test Configuration (Edit this section when adding new tests) ---
+LUO_SHARED_SRCS := luo_test_utils.c
+LUO_SHARED_HDRS += luo_test_utils.h
+
+LUO_MANUAL_TESTS += luo_kexec_simple
+
+TEST_FILES += do_kexec.sh
TEST_GEN_PROGS += liveupdate
+# --- Automatic Rule Generation (Do not edit below) ---
+
+TEST_GEN_PROGS_EXTENDED += $(LUO_MANUAL_TESTS)
+
+# Define the full list of sources for each manual test.
+$(foreach test,$(LUO_MANUAL_TESTS), \
+ $(eval $(test)_SOURCES := $(test).c $(LUO_SHARED_SRCS)))
+
+# This loop automatically generates an explicit build rule for each manual test.
+# It includes dependencies on the shared headers and makes the output
+# executable.
+# Note the use of '$$' to escape automatic variables for the 'eval' command.
+$(foreach test,$(LUO_MANUAL_TESTS), \
+ $(eval $(OUTPUT)/$(test): $($(test)_SOURCES) $(LUO_SHARED_HDRS) \
+ $(call msg,LINK,,$$@) ; \
+ $(Q)$(LINK.c) $$^ $(LDLIBS) -o $$@ ; \
+ $(Q)chmod +x $$@ \
+ ) \
+)
+
include ../lib.mk
diff --git a/tools/testing/selftests/liveupdate/do_kexec.sh b/tools/testing/selftests/liveupdate/do_kexec.sh
new file mode 100755
index 000000000000..3c7c6cafbef8
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/do_kexec.sh
@@ -0,0 +1,16 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+set -e
+
+# Use $KERNEL and $INITRAMFS to pass custom Kernel and optional initramfs
+
+KERNEL="${KERNEL:-/boot/bzImage}"
+set -- -l -s --reuse-cmdline "$KERNEL"
+
+INITRAMFS="${INITRAMFS:-/boot/initramfs}"
+if [ -f "$INITRAMFS" ]; then
+ set -- "$@" --initrd="$INITRAMFS"
+fi
+
+kexec "$@"
+kexec -e
diff --git a/tools/testing/selftests/liveupdate/luo_kexec_simple.c b/tools/testing/selftests/liveupdate/luo_kexec_simple.c
new file mode 100644
index 000000000000..67ab6ebf9eec
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/luo_kexec_simple.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ *
+ * A simple selftest to validate the end-to-end lifecycle of a LUO session
+ * across a single kexec reboot.
+ */
+
+#include "luo_test_utils.h"
+
+/* Test-specific constants are now defined locally */
+#define KEXEC_SCRIPT "./do_kexec.sh"
+#define TEST_SESSION_NAME "test-session"
+#define TEST_MEMFD_TOKEN 0x1A
+#define TEST_MEMFD_DATA "hello kexec world"
+
+/* Constants for the state-tracking mechanism, specific to this test file. */
+#define STATE_SESSION_NAME "kexec_simple_state"
+#define STATE_MEMFD_TOKEN 999
+
+/* Stage 1: Executed before the kexec reboot. */
+static void run_stage_1(int luo_fd)
+{
+ int session_fd;
+
+ ksft_print_msg("[STAGE 1] Starting pre-kexec setup...\n");
+
+ ksft_print_msg("[STAGE 1] Creating state file for next stage (2)...\n");
+ create_state_file(luo_fd, STATE_SESSION_NAME, STATE_MEMFD_TOKEN, 2);
+
+ ksft_print_msg("[STAGE 1] Creating session '%s' and preserving memfd...\n",
+ TEST_SESSION_NAME);
+ session_fd = luo_create_session(luo_fd, TEST_SESSION_NAME);
+ if (session_fd < 0)
+ fail_exit("luo_create_session for '%s'", TEST_SESSION_NAME);
+
+ if (create_and_preserve_memfd(session_fd, TEST_MEMFD_TOKEN,
+ TEST_MEMFD_DATA) < 0) {
+ fail_exit("create_and_preserve_memfd for token %#x",
+ TEST_MEMFD_TOKEN);
+ }
+
+ ksft_print_msg("[STAGE 1] Executing kexec...\n");
+ if (system(KEXEC_SCRIPT) != 0)
+ fail_exit("kexec script failed");
+ exit(EXIT_FAILURE);
+}
+
+/* Stage 2: Executed after the kexec reboot. */
+static void run_stage_2(int luo_fd, int state_session_fd)
+{
+ int session_fd, mfd, stage;
+
+ ksft_print_msg("[STAGE 2] Starting post-kexec verification...\n");
+
+ restore_and_read_stage(state_session_fd, STATE_MEMFD_TOKEN, &stage);
+ if (stage != 2)
+ fail_exit("Expected stage 2, but state file contains %d", stage);
+
+ ksft_print_msg("[STAGE 2] Retrieving session '%s'...\n", TEST_SESSION_NAME);
+ session_fd = luo_retrieve_session(luo_fd, TEST_SESSION_NAME);
+ if (session_fd < 0)
+ fail_exit("luo_retrieve_session for '%s'", TEST_SESSION_NAME);
+
+ ksft_print_msg("[STAGE 2] Restoring and verifying memfd (token %#x)...\n",
+ TEST_MEMFD_TOKEN);
+ mfd = restore_and_verify_memfd(session_fd, TEST_MEMFD_TOKEN,
+ TEST_MEMFD_DATA);
+ if (mfd < 0)
+ fail_exit("restore_and_verify_memfd for token %#x", TEST_MEMFD_TOKEN);
+ close(mfd);
+
+ ksft_print_msg("[STAGE 2] Test data verified successfully.\n");
+ ksft_print_msg("[STAGE 2] Finalizing test session...\n");
+ if (luo_session_finish(session_fd) < 0)
+ fail_exit("luo_session_finish for test session");
+ close(session_fd);
+
+ ksft_print_msg("[STAGE 2] Finalizing state session...\n");
+ if (luo_session_finish(state_session_fd) < 0)
+ fail_exit("luo_session_finish for state session");
+ close(state_session_fd);
+
+ ksft_print_msg("\n--- SIMPLE KEXEC TEST PASSED ---\n");
+}
+
+int main(int argc, char *argv[])
+{
+ int luo_fd;
+ int state_session_fd;
+
+ luo_fd = luo_open_device();
+ if (luo_fd < 0)
+ ksft_exit_skip("Failed to open %s. Is the luo module loaded?\n",
+ LUO_DEVICE);
+
+ /*
+ * Determine the stage by attempting to retrieve the state session.
+ * If it doesn't exist (ENOENT), we are in Stage 1 (pre-kexec).
+ */
+ state_session_fd = luo_retrieve_session(luo_fd, STATE_SESSION_NAME);
+ if (state_session_fd == -ENOENT) {
+ run_stage_1(luo_fd);
+ } else if (state_session_fd >= 0) {
+ /* We got a valid handle, pass it directly to stage 2 */
+ run_stage_2(luo_fd, state_session_fd);
+ } else {
+ fail_exit("Failed to check for state session");
+ }
+
+ close(luo_fd);
+}
diff --git a/tools/testing/selftests/liveupdate/luo_test_utils.c b/tools/testing/selftests/liveupdate/luo_test_utils.c
new file mode 100644
index 000000000000..0a24105cbc54
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/luo_test_utils.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <stdarg.h>
+
+#include "luo_test_utils.h"
+
+int luo_open_device(void)
+{
+ return open(LUO_DEVICE, O_RDWR);
+}
+
+int luo_create_session(int luo_fd, const char *name)
+{
+ struct liveupdate_ioctl_create_session arg = { .size = sizeof(arg) };
+
+ snprintf((char *)arg.name, LIVEUPDATE_SESSION_NAME_LENGTH, "%.*s",
+ LIVEUPDATE_SESSION_NAME_LENGTH - 1, name);
+
+ if (ioctl(luo_fd, LIVEUPDATE_IOCTL_CREATE_SESSION, &arg) < 0)
+ return -errno;
+
+ return arg.fd;
+}
+
+int luo_retrieve_session(int luo_fd, const char *name)
+{
+ struct liveupdate_ioctl_retrieve_session arg = { .size = sizeof(arg) };
+
+ snprintf((char *)arg.name, LIVEUPDATE_SESSION_NAME_LENGTH, "%.*s",
+ LIVEUPDATE_SESSION_NAME_LENGTH - 1, name);
+
+ if (ioctl(luo_fd, LIVEUPDATE_IOCTL_RETRIEVE_SESSION, &arg) < 0)
+ return -errno;
+
+ return arg.fd;
+}
+
+int create_and_preserve_memfd(int session_fd, int token, const char *data)
+{
+ struct liveupdate_session_preserve_fd arg = { .size = sizeof(arg) };
+ long page_size = sysconf(_SC_PAGE_SIZE);
+ void *map = MAP_FAILED;
+ int mfd = -1, ret = -1;
+
+ mfd = memfd_create("test_mfd", 0);
+ if (mfd < 0)
+ return -errno;
+
+ if (ftruncate(mfd, page_size) != 0)
+ goto out;
+
+ map = mmap(NULL, page_size, PROT_WRITE, MAP_SHARED, mfd, 0);
+ if (map == MAP_FAILED)
+ goto out;
+
+ snprintf(map, page_size, "%s", data);
+ munmap(map, page_size);
+
+ arg.fd = mfd;
+ arg.token = token;
+ if (ioctl(session_fd, LIVEUPDATE_SESSION_PRESERVE_FD, &arg) < 0)
+ goto out;
+
+ ret = 0;
+out:
+ if (ret != 0 && errno != 0)
+ ret = -errno;
+ if (mfd >= 0)
+ close(mfd);
+ return ret;
+}
+
+int restore_and_verify_memfd(int session_fd, int token,
+ const char *expected_data)
+{
+ struct liveupdate_session_retrieve_fd arg = { .size = sizeof(arg) };
+ long page_size = sysconf(_SC_PAGE_SIZE);
+ void *map = MAP_FAILED;
+ int mfd = -1, ret = -1;
+
+ arg.token = token;
+ if (ioctl(session_fd, LIVEUPDATE_SESSION_RETRIEVE_FD, &arg) < 0)
+ return -errno;
+ mfd = arg.fd;
+
+ map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, mfd, 0);
+ if (map == MAP_FAILED)
+ goto out;
+
+ if (expected_data && strcmp(expected_data, map) != 0) {
+ ksft_print_msg("Data mismatch! Expected '%s', Got '%s'\n",
+ expected_data, (char *)map);
+ ret = -EINVAL;
+ goto out_munmap;
+ }
+
+ ret = mfd;
+out_munmap:
+ munmap(map, page_size);
+out:
+ if (ret < 0 && errno != 0)
+ ret = -errno;
+ if (ret < 0 && mfd >= 0)
+ close(mfd);
+ return ret;
+}
+
+int luo_session_finish(int session_fd)
+{
+ struct liveupdate_session_finish arg = { .size = sizeof(arg) };
+
+ if (ioctl(session_fd, LIVEUPDATE_SESSION_FINISH, &arg) < 0)
+ return -errno;
+
+ return 0;
+}
+
+void create_state_file(int luo_fd, const char *session_name, int token,
+ int next_stage)
+{
+ char buf[32];
+ int state_session_fd;
+
+ state_session_fd = luo_create_session(luo_fd, session_name);
+ if (state_session_fd < 0)
+ fail_exit("luo_create_session for state tracking");
+
+ snprintf(buf, sizeof(buf), "%d", next_stage);
+ if (create_and_preserve_memfd(state_session_fd, token, buf) < 0)
+ fail_exit("create_and_preserve_memfd for state tracking");
+
+ /*
+ * DO NOT close session FD, otherwise it is going to be unpreserved
+ */
+}
+
+void restore_and_read_stage(int state_session_fd, int token, int *stage)
+{
+ char buf[32] = {0};
+ int mfd;
+
+ mfd = restore_and_verify_memfd(state_session_fd, token, NULL);
+ if (mfd < 0)
+ fail_exit("failed to restore state memfd");
+
+ if (read(mfd, buf, sizeof(buf) - 1) < 0)
+ fail_exit("failed to read state mfd");
+
+ *stage = atoi(buf);
+
+ close(mfd);
+}
diff --git a/tools/testing/selftests/liveupdate/luo_test_utils.h b/tools/testing/selftests/liveupdate/luo_test_utils.h
new file mode 100644
index 000000000000..093e787b9f4b
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/luo_test_utils.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ *
+ * Utility functions for LUO kselftests.
+ */
+
+#ifndef LUO_TEST_UTILS_H
+#define LUO_TEST_UTILS_H
+
+#include <errno.h>
+#include <string.h>
+#include <linux/liveupdate.h>
+#include "../kselftest.h"
+
+#define LUO_DEVICE "/dev/liveupdate"
+
+#define fail_exit(fmt, ...) \
+ ksft_exit_fail_msg("[%s:%d] " fmt " (errno: %s)\n", \
+ __func__, __LINE__, ##__VA_ARGS__, strerror(errno))
+
+/* Generic LUO and session management helpers */
+int luo_open_device(void);
+int luo_create_session(int luo_fd, const char *name);
+int luo_retrieve_session(int luo_fd, const char *name);
+int luo_session_finish(int session_fd);
+
+/* Generic file preservation and restoration helpers */
+int create_and_preserve_memfd(int session_fd, int token, const char *data);
+int restore_and_verify_memfd(int session_fd, int token, const char *expected_data);
+
+/* Kexec state-tracking helpers */
+void create_state_file(int luo_fd, const char *session_name, int token,
+ int next_stage);
+void restore_and_read_stage(int state_session_fd, int token, int *stage);
+
+#endif /* LUO_TEST_UTILS_H */
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 19/20] selftests/liveupdate: Add kexec test for multiple and empty sessions
From: Pasha Tatashin @ 2025-11-15 23:34 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
Introduce a new kexec-based selftest, luo_kexec_multi_session, to
validate the end-to-end lifecycle of a more complex LUO scenario.
While the existing luo_kexec_simple test covers the basic end-to-end
lifecycle, it is limited to a single session with one preserved file.
This new test significantly expands coverage by verifying LUO's ability
to handle a mixed workload involving multiple sessions, some of which
are intentionally empty. This ensures that the LUO core correctly
preserves and restores the state of all session types across a reboot.
The test validates the following sequence:
Stage 1 (Pre-kexec):
- Creates two empty test sessions (multi-test-empty-1,
multi-test-empty-2).
- Creates a session with one preserved memfd (multi-test-files-1).
- Creates another session with two preserved memfds
(multi-test-files-2), each containing unique data.
- Creates a state-tracking session to manage the transition to
Stage 2.
- Executes a kexec reboot via the helper script.
Stage 2 (Post-kexec):
- Retrieves the state-tracking session to confirm it is in the
post-reboot stage.
- Retrieves all four test sessions (both the empty and non-empty
ones).
- For the non-empty sessions, restores the preserved memfds and
verifies their contents match the original data patterns.
- Finalizes all test sessions and the state session to ensure a clean
teardown and that all associated kernel resources are correctly
released.
This test provides greater confidence in the robustness of the LUO
framework by validating its behavior in a more realistic, multi-faceted
scenario.
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
tools/testing/selftests/liveupdate/.gitignore | 1 +
tools/testing/selftests/liveupdate/Makefile | 1 +
.../selftests/liveupdate/luo_multi_session.c | 190 ++++++++++++++++++
3 files changed, 192 insertions(+)
create mode 100644 tools/testing/selftests/liveupdate/luo_multi_session.c
diff --git a/tools/testing/selftests/liveupdate/.gitignore b/tools/testing/selftests/liveupdate/.gitignore
index daeef116174d..42a15a8d5d9e 100644
--- a/tools/testing/selftests/liveupdate/.gitignore
+++ b/tools/testing/selftests/liveupdate/.gitignore
@@ -1,2 +1,3 @@
/liveupdate
/luo_kexec_simple
+/luo_multi_session
diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
index 1563ac84006a..6ee6efeec62d 100644
--- a/tools/testing/selftests/liveupdate/Makefile
+++ b/tools/testing/selftests/liveupdate/Makefile
@@ -11,6 +11,7 @@ LUO_SHARED_SRCS := luo_test_utils.c
LUO_SHARED_HDRS += luo_test_utils.h
LUO_MANUAL_TESTS += luo_kexec_simple
+LUO_MANUAL_TESTS += luo_multi_session
TEST_FILES += do_kexec.sh
diff --git a/tools/testing/selftests/liveupdate/luo_multi_session.c b/tools/testing/selftests/liveupdate/luo_multi_session.c
new file mode 100644
index 000000000000..c9955f1b6e97
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/luo_multi_session.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ *
+ * A selftest to validate the end-to-end lifecycle of multiple LUO sessions
+ * across a kexec reboot, including empty sessions and sessions with multiple
+ * files.
+ */
+
+#include "luo_test_utils.h"
+
+#define KEXEC_SCRIPT "./do_kexec.sh"
+
+#define SESSION_EMPTY_1 "multi-test-empty-1"
+#define SESSION_EMPTY_2 "multi-test-empty-2"
+#define SESSION_FILES_1 "multi-test-files-1"
+#define SESSION_FILES_2 "multi-test-files-2"
+
+#define MFD1_TOKEN 0x1001
+#define MFD2_TOKEN 0x2002
+#define MFD3_TOKEN 0x3003
+
+#define MFD1_DATA "Data for session files 1"
+#define MFD2_DATA "First file for session files 2"
+#define MFD3_DATA "Second file for session files 2"
+
+#define STATE_SESSION_NAME "kexec_multi_state"
+#define STATE_MEMFD_TOKEN 998
+
+/* Stage 1: Executed before the kexec reboot. */
+static void run_stage_1(int luo_fd)
+{
+ int s_empty1_fd, s_empty2_fd, s_files1_fd, s_files2_fd;
+
+ ksft_print_msg("[STAGE 1] Starting pre-kexec setup for multi-session test...\n");
+
+ ksft_print_msg("[STAGE 1] Creating state file for next stage (2)...\n");
+ create_state_file(luo_fd, STATE_SESSION_NAME, STATE_MEMFD_TOKEN, 2);
+
+ ksft_print_msg("[STAGE 1] Creating empty sessions '%s' and '%s'...\n",
+ SESSION_EMPTY_1, SESSION_EMPTY_2);
+ s_empty1_fd = luo_create_session(luo_fd, SESSION_EMPTY_1);
+ if (s_empty1_fd < 0)
+ fail_exit("luo_create_session for '%s'", SESSION_EMPTY_1);
+
+ s_empty2_fd = luo_create_session(luo_fd, SESSION_EMPTY_2);
+ if (s_empty2_fd < 0)
+ fail_exit("luo_create_session for '%s'", SESSION_EMPTY_2);
+
+ ksft_print_msg("[STAGE 1] Creating session '%s' with one memfd...\n",
+ SESSION_FILES_1);
+
+ s_files1_fd = luo_create_session(luo_fd, SESSION_FILES_1);
+ if (s_files1_fd < 0)
+ fail_exit("luo_create_session for '%s'", SESSION_FILES_1);
+ if (create_and_preserve_memfd(s_files1_fd, MFD1_TOKEN, MFD1_DATA) < 0) {
+ fail_exit("create_and_preserve_memfd for token %#x",
+ MFD1_TOKEN);
+ }
+
+ ksft_print_msg("[STAGE 1] Creating session '%s' with two memfds...\n",
+ SESSION_FILES_2);
+
+ s_files2_fd = luo_create_session(luo_fd, SESSION_FILES_2);
+ if (s_files2_fd < 0)
+ fail_exit("luo_create_session for '%s'", SESSION_FILES_2);
+ if (create_and_preserve_memfd(s_files2_fd, MFD2_TOKEN, MFD2_DATA) < 0) {
+ fail_exit("create_and_preserve_memfd for token %#x",
+ MFD2_TOKEN);
+ }
+ if (create_and_preserve_memfd(s_files2_fd, MFD3_TOKEN, MFD3_DATA) < 0) {
+ fail_exit("create_and_preserve_memfd for token %#x",
+ MFD3_TOKEN);
+ }
+
+ ksft_print_msg("[STAGE 1] Executing kexec...\n");
+
+ if (system(KEXEC_SCRIPT) != 0)
+ fail_exit("kexec script failed");
+
+ exit(EXIT_FAILURE);
+}
+
+/* Stage 2: Executed after the kexec reboot. */
+static void run_stage_2(int luo_fd, int state_session_fd)
+{
+ int s_empty1_fd, s_empty2_fd, s_files1_fd, s_files2_fd;
+ int mfd1, mfd2, mfd3, stage;
+
+ ksft_print_msg("[STAGE 2] Starting post-kexec verification...\n");
+
+ restore_and_read_stage(state_session_fd, STATE_MEMFD_TOKEN, &stage);
+ if (stage != 2) {
+ fail_exit("Expected stage 2, but state file contains %d",
+ stage);
+ }
+
+ ksft_print_msg("[STAGE 2] Retrieving all sessions...\n");
+ s_empty1_fd = luo_retrieve_session(luo_fd, SESSION_EMPTY_1);
+ if (s_empty1_fd < 0)
+ fail_exit("luo_retrieve_session for '%s'", SESSION_EMPTY_1);
+
+ s_empty2_fd = luo_retrieve_session(luo_fd, SESSION_EMPTY_2);
+ if (s_empty2_fd < 0)
+ fail_exit("luo_retrieve_session for '%s'", SESSION_EMPTY_2);
+
+ s_files1_fd = luo_retrieve_session(luo_fd, SESSION_FILES_1);
+ if (s_files1_fd < 0)
+ fail_exit("luo_retrieve_session for '%s'", SESSION_FILES_1);
+
+ s_files2_fd = luo_retrieve_session(luo_fd, SESSION_FILES_2);
+ if (s_files2_fd < 0)
+ fail_exit("luo_retrieve_session for '%s'", SESSION_FILES_2);
+
+ ksft_print_msg("[STAGE 2] Verifying contents of session '%s'...\n",
+ SESSION_FILES_1);
+ mfd1 = restore_and_verify_memfd(s_files1_fd, MFD1_TOKEN, MFD1_DATA);
+ if (mfd1 < 0)
+ fail_exit("restore_and_verify_memfd for token %#x", MFD1_TOKEN);
+ close(mfd1);
+
+ ksft_print_msg("[STAGE 2] Verifying contents of session '%s'...\n",
+ SESSION_FILES_2);
+
+ mfd2 = restore_and_verify_memfd(s_files2_fd, MFD2_TOKEN, MFD2_DATA);
+ if (mfd2 < 0)
+ fail_exit("restore_and_verify_memfd for token %#x", MFD2_TOKEN);
+ close(mfd2);
+
+ mfd3 = restore_and_verify_memfd(s_files2_fd, MFD3_TOKEN, MFD3_DATA);
+ if (mfd3 < 0)
+ fail_exit("restore_and_verify_memfd for token %#x", MFD3_TOKEN);
+ close(mfd3);
+
+ ksft_print_msg("[STAGE 2] Test data verified successfully.\n");
+
+ ksft_print_msg("[STAGE 2] Finalizing all test sessions...\n");
+ if (luo_session_finish(s_empty1_fd) < 0)
+ fail_exit("luo_session_finish for '%s'", SESSION_EMPTY_1);
+ close(s_empty1_fd);
+
+ if (luo_session_finish(s_empty2_fd) < 0)
+ fail_exit("luo_session_finish for '%s'", SESSION_EMPTY_2);
+ close(s_empty2_fd);
+
+ if (luo_session_finish(s_files1_fd) < 0)
+ fail_exit("luo_session_finish for '%s'", SESSION_FILES_1);
+ close(s_files1_fd);
+
+ if (luo_session_finish(s_files2_fd) < 0)
+ fail_exit("luo_session_finish for '%s'", SESSION_FILES_2);
+ close(s_files2_fd);
+
+ ksft_print_msg("[STAGE 2] Finalizing state session...\n");
+ if (luo_session_finish(state_session_fd) < 0)
+ fail_exit("luo_session_finish for state session");
+ close(state_session_fd);
+
+ ksft_print_msg("\n--- MULTI-SESSION KEXEC TEST PASSED ---\n");
+}
+
+int main(int argc, char *argv[])
+{
+ int luo_fd;
+ int state_session_fd;
+
+ luo_fd = luo_open_device();
+ if (luo_fd < 0)
+ ksft_exit_skip("Failed to open %s. Is the luo module loaded?\n",
+ LUO_DEVICE);
+
+ /*
+ * Determine the stage by attempting to retrieve the state session.
+ * If it doesn't exist (ENOENT), we are in Stage 1 (pre-kexec).
+ */
+ state_session_fd = luo_retrieve_session(luo_fd, STATE_SESSION_NAME);
+ if (state_session_fd == -ENOENT) {
+ run_stage_1(luo_fd);
+ } else if (state_session_fd >= 0) {
+ /* We got a valid handle, pass it directly to stage 2 */
+ run_stage_2(luo_fd, state_session_fd);
+ } else {
+ fail_exit("Failed to check for state session");
+ }
+
+ close(luo_fd);
+ return 0;
+}
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* [PATCH v6 20/20] tests/liveupdate: Add in-kernel liveupdate test
From: Pasha Tatashin @ 2025-11-15 23:34 UTC (permalink / raw)
To: pratyush, jasonmiu, graf, pasha.tatashin, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-1-pasha.tatashin@soleen.com>
Introduce an in-kernel test module to validate the core logic of the
Live Update Orchestrator's File-Lifecycle-Bound feature. This
provides a low-level, controlled environment to test FLB registration
and callback invocation without requiring userspace interaction or
actual kexec reboots.
The test is enabled by the CONFIG_LIVEUPDATE_TEST Kconfig option.
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
include/linux/liveupdate/abi/luo.h | 5 +
kernel/liveupdate/luo_file.c | 2 +
kernel/liveupdate/luo_internal.h | 6 ++
lib/Kconfig.debug | 23 +++++
lib/tests/Makefile | 1 +
lib/tests/liveupdate.c | 143 +++++++++++++++++++++++++++++
6 files changed, 180 insertions(+)
create mode 100644 lib/tests/liveupdate.c
diff --git a/include/linux/liveupdate/abi/luo.h b/include/linux/liveupdate/abi/luo.h
index 85596ce68c16..cdcace9b48f5 100644
--- a/include/linux/liveupdate/abi/luo.h
+++ b/include/linux/liveupdate/abi/luo.h
@@ -230,4 +230,9 @@ struct luo_flb_ser {
u64 count;
} __packed;
+/* Kernel Live Update Test ABI */
+#ifdef CONFIG_LIVEUPDATE_TEST
+#define LIVEUPDATE_TEST_FLB_COMPATIBLE(i) "liveupdate-test-flb-v" #i
+#endif
+
#endif /* _LINUX_LIVEUPDATE_ABI_LUO_H */
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index df337c9c4f21..9a531096bdb5 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -834,6 +834,8 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
INIT_LIST_HEAD(&fh->flb_list);
list_add_tail(&fh->list, &luo_file_handler_list);
+ liveupdate_test_register(fh);
+
return 0;
}
diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
index 389fb102775f..c863cb051d49 100644
--- a/kernel/liveupdate/luo_internal.h
+++ b/kernel/liveupdate/luo_internal.h
@@ -86,4 +86,10 @@ int __init luo_flb_setup_outgoing(void *fdt);
int __init luo_flb_setup_incoming(void *fdt);
void luo_flb_serialize(void);
+#ifdef CONFIG_LIVEUPDATE_TEST
+void liveupdate_test_register(struct liveupdate_file_handler *h);
+#else
+static inline void liveupdate_test_register(struct liveupdate_file_handler *h) { }
+#endif
+
#endif /* _LINUX_LUO_INTERNAL_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9a087826498a..eaa2af2bd963 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2803,6 +2803,29 @@ config LINEAR_RANGES_TEST
If unsure, say N.
+config LIVEUPDATE_TEST
+ bool "Live Update Kernel Test"
+ default n
+ depends on LIVEUPDATE
+ help
+ Enable a built-in kernel test module for the Live Update
+ Orchestrator.
+
+ This module validates the File-Lifecycle-Bound subsystem by
+ registering a set of mock FLB objects with any real file handlers
+ that support live update (such as the memfd handler).
+
+ When live update operations are performed, this test module will
+ output messages to the kernel log (dmesg), confirming that its
+ registration and various callback functions (preserve, retrieve,
+ finish, etc.) are being invoked correctly.
+
+ This is a debugging and regression testing tool for developers
+ working on the Live Update subsystem. It should not be enabled in
+ production kernels.
+
+ If unsure, say N
+
config CMDLINE_KUNIT_TEST
tristate "KUnit test for cmdline API" if !KUNIT_ALL_TESTS
depends on KUNIT
diff --git a/lib/tests/Makefile b/lib/tests/Makefile
index f7460831cfdd..8e5c527a94ac 100644
--- a/lib/tests/Makefile
+++ b/lib/tests/Makefile
@@ -27,6 +27,7 @@ obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
obj-$(CONFIG_KFIFO_KUNIT_TEST) += kfifo_kunit.o
obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o
+obj-$(CONFIG_LIVEUPDATE_TEST) += liveupdate.o
CFLAGS_longest_symbol_kunit.o += $(call cc-disable-warning, missing-prototypes)
obj-$(CONFIG_LONGEST_SYM_KUNIT_TEST) += longest_symbol_kunit.o
diff --git a/lib/tests/liveupdate.c b/lib/tests/liveupdate.c
new file mode 100644
index 000000000000..05c05b8c1c22
--- /dev/null
+++ b/lib/tests/liveupdate.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME " test: " fmt
+
+#include <linux/cleanup.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/liveupdate.h>
+#include <linux/module.h>
+#include "../../kernel/liveupdate/luo_internal.h"
+
+static const struct liveupdate_flb_ops test_flb_ops;
+#define DEFINE_TEST_FLB(i) { \
+ .ops = &test_flb_ops, \
+ .compatible = LIVEUPDATE_TEST_FLB_COMPATIBLE(i), \
+}
+
+/* Number of Test FLBs to register with every file handler */
+#define TEST_NFLBS 3
+static struct liveupdate_flb test_flbs[TEST_NFLBS] = {
+ DEFINE_TEST_FLB(0),
+ DEFINE_TEST_FLB(1),
+ DEFINE_TEST_FLB(2),
+};
+
+#define TEST_FLB_MAGIC_BASE 0xFEEDF00DCAFEBEE0ULL
+
+static int test_flb_preserve(struct liveupdate_flb_op_args *argp)
+{
+ ptrdiff_t index = argp->flb - test_flbs;
+
+ pr_info("%s: preserve was triggered\n", argp->flb->compatible);
+ argp->data = TEST_FLB_MAGIC_BASE + index;
+
+ return 0;
+}
+
+static void test_flb_unpreserve(struct liveupdate_flb_op_args *argp)
+{
+ pr_info("%s: unpreserve was triggered\n", argp->flb->compatible);
+}
+
+static int test_flb_retrieve(struct liveupdate_flb_op_args *argp)
+{
+ ptrdiff_t index = argp->flb - test_flbs;
+ u64 expected_data = TEST_FLB_MAGIC_BASE + index;
+
+ if (argp->data == expected_data) {
+ pr_info("%s: found flb data from the previous boot\n",
+ argp->flb->compatible);
+ argp->obj = (void *)argp->data;
+ } else {
+ pr_err("%s: ERROR - incorrect data handle: %llx, expected %llx\n",
+ argp->flb->compatible, argp->data, expected_data);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static void test_flb_finish(struct liveupdate_flb_op_args *argp)
+{
+ ptrdiff_t index = argp->flb - test_flbs;
+ void *expected_obj = (void *)(TEST_FLB_MAGIC_BASE + index);
+
+ if (argp->obj == expected_obj) {
+ pr_info("%s: finish was triggered\n", argp->flb->compatible);
+ } else {
+ pr_err("%s: ERROR - finish called with invalid object\n",
+ argp->flb->compatible);
+ }
+}
+
+static const struct liveupdate_flb_ops test_flb_ops = {
+ .preserve = test_flb_preserve,
+ .unpreserve = test_flb_unpreserve,
+ .retrieve = test_flb_retrieve,
+ .finish = test_flb_finish,
+ .owner = THIS_MODULE,
+};
+
+static void liveupdate_test_init(void)
+{
+ static DEFINE_MUTEX(init_lock);
+ static bool initialized;
+ int i;
+
+ guard(mutex)(&init_lock);
+
+ if (initialized)
+ return;
+
+ for (i = 0; i < TEST_NFLBS; i++) {
+ struct liveupdate_flb *flb = &test_flbs[i];
+ void *obj;
+ int err;
+
+ liveupdate_init_flb(flb);
+
+ err = liveupdate_flb_incoming_locked(flb, &obj);
+ if (!err) {
+ liveupdate_flb_incoming_unlock(flb, obj);
+ } else if (err != -ENODATA && err != -ENOENT) {
+ pr_err("liveupdate_flb_incoming_locked for %s failed: %pe\n",
+ flb->compatible, ERR_PTR(err));
+ }
+ }
+ initialized = true;
+}
+
+void liveupdate_test_register(struct liveupdate_file_handler *h)
+{
+ int err, i;
+
+ liveupdate_test_init();
+
+ for (i = 0; i < TEST_NFLBS; i++) {
+ struct liveupdate_flb *flb = &test_flbs[i];
+
+ err = liveupdate_register_flb(h, flb);
+ if (err)
+ pr_err("Failed to register %s %pe\n",
+ flb->compatible, ERR_PTR(err));
+ }
+
+ err = liveupdate_register_flb(h, &test_flbs[0]);
+ if (!err || err != -EEXIST) {
+ pr_err("Failed: %s should be already registered, but got err: %pe\n",
+ test_flbs[0].compatible, ERR_PTR(err));
+ }
+
+ pr_info("Registered %d FLBs with file handler: [%s]\n",
+ TEST_NFLBS, h->compatible);
+}
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Pasha Tatashin <pasha.tatashin@soleen.com>");
+MODULE_DESCRIPTION("In-kernel test for LUO mechanism");
--
2.52.0.rc1.455.g30608eb744-goog
^ permalink raw reply related
* Re: RFC: Serial port DTR/RTS - O_<something>
From: H. Peter Anvin @ 2025-11-16 0:47 UTC (permalink / raw)
To: Ned Ulbricht, Maciej W. Rozycki
Cc: Greg KH, Theodore Ts'o, Maarten Brock,
linux-serial@vger.kernel.org, linux-api@vger.kernel.org, LKML
In-Reply-To: <6c26eea2-6f90-f48a-9488-e7480f086c70@netscape.net>
On 2025-11-15 13:29, Ned Ulbricht wrote:
> |
> | O_TTY_INIT
>
> https://pubs.opengroup.org/onlinepubs/9799919799/
>
> That's what motivates my first-glance preference to name this new flag,
> which will have approximately opposite behavior, as O_TTY_NOINIT.
>
> But as a generic abstraction, I more prefer O_KEEP.
>
O_KEEP seems a little vague, but O_KEEPCONFIG seems like a decent name.
It seems like we don't have several new flags:
O_EXEC
O_SEARCH
O_CLOFORK
O_TTY_INIT
O_RSYNC
O_NOCLOBBER
Some of them *may* be possible to construct with existing Linux options, I'm
not 100% sure; in particular O_SEARCH might be the same as (O_DIRECTORY|O_PATH).
O_NOCLOBBER looks like an odd in-between between O_EXCL and
(O_EXCL|O_NOFOLLOW); stated to be specifically to implement the shell
"noclobber" semantic.
-hpa
^ permalink raw reply
* Re: [PATCH v6 02/20] liveupdate: luo_core: integrate with KHO
From: Mike Rapoport @ 2025-11-16 12:43 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-3-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:48PM -0500, Pasha Tatashin wrote:
> Integrate the LUO with the KHO framework to enable passing LUO state
> across a kexec reboot.
>
> When LUO is transitioned to a "prepared" state, it tells KHO to
> finalize, so all memory segments that were added to KHO preservation
> list are getting preserved. After "Prepared" state no new segments
> can be preserved. If LUO is canceled, it also tells KHO to cancel the
> serialization, and therefore, later LUO can go back into the prepared
> state.
>
> This patch introduces the following changes:
> - During the KHO finalization phase allocate FDT blob.
This happens much earlier, isn't it?
> - Populate this FDT with a LUO compatibility string ("luo-v1").
>
> LUO now depends on `CONFIG_KEXEC_HANDOVER`. The core state transition
> logic (`luo_do_*_calls`) remains unimplemented in this patch.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/linux/liveupdate/abi/luo.h | 54 ++++++++++
> kernel/liveupdate/luo_core.c | 153 ++++++++++++++++++++++++++++-
> 2 files changed, 206 insertions(+), 1 deletion(-)
> create mode 100644 include/linux/liveupdate/abi/luo.h
>
> diff --git a/include/linux/liveupdate/abi/luo.h b/include/linux/liveupdate/abi/luo.h
> new file mode 100644
> index 000000000000..9483a294287f
> --- /dev/null
> +++ b/include/linux/liveupdate/abi/luo.h
> @@ -0,0 +1,54 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Copyright (c) 2025, Google LLC.
> + * Pasha Tatashin <pasha.tatashin@soleen.com>
> + */
> +
> +/**
> + * DOC: Live Update Orchestrator ABI
> + *
> + * This header defines the stable Application Binary Interface used by the
> + * Live Update Orchestrator to pass state from a pre-update kernel to a
> + * post-update kernel. The ABI is built upon the Kexec HandOver framework
> + * and uses a Flattened Device Tree to describe the preserved data.
> + *
> + * This interface is a contract. Any modification to the FDT structure, node
> + * properties, compatible strings, or the layout of the `__packed` serialization
> + * structures defined here constitutes a breaking change. Such changes require
> + * incrementing the version number in the relevant `_COMPATIBLE` string to
> + * prevent a new kernel from misinterpreting data from an old kernel.
I'd add a sentence that stresses that ABI changes are possible as long they
include changes to the FDT version.
This is indeed implied by the last paragraph, but I think it's worth
spelling it explicitly.
Another thing that I think this should mention is that compatibility is
only guaranteed for the kernels that use the same ABI version.
> + *
> + * FDT Structure Overview:
> + * The entire LUO state is encapsulated within a single KHO entry named "LUO".
> + * This entry contains an FDT with the following layout:
> + *
> + * .. code-block:: none
> + *
> + * / {
> + * compatible = "luo-v1";
> + * liveupdate-number = <...>;
> + * };
> + *
> + * Main LUO Node (/):
> + *
> + * - compatible: "luo-v1"
> + * Identifies the overall LUO ABI version.
> + * - liveupdate-number: u64
> + * A counter tracking the number of successful live updates performed.
> + */
...
> +static int __init liveupdate_early_init(void)
> +{
> + int err;
> +
> + err = luo_early_startup();
> + if (err) {
> + pr_err("The incoming tree failed to initialize properly [%pe], disabling live update\n",
> + ERR_PTR(err));
How do we report this to the userspace?
I think the decision what to do in this case belongs there. Even if it's
down to choosing between plain kexec and full reboot, it's still a policy
that should be implemented in userspace.
> + luo_global.enabled = false;
> + }
> +
> + return err;
> +}
> +early_initcall(liveupdate_early_init);
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 03/20] kexec: call liveupdate_reboot() before kexec
From: Mike Rapoport @ 2025-11-16 12:44 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-4-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:49PM -0500, Pasha Tatashin wrote:
> Modify the kernel_kexec() to call liveupdate_reboot().
>
> This ensures that the Live Update Orchestrator is notified just
> before the kernel executes the kexec jump. The liveupdate_reboot()
> function triggers the final freeze event, allowing participating
> FDs perform last-minute check or state saving within the blackout
> window.
>
> If liveupdate_reboot() returns an error (indicating a failure during
> LUO finalization), the kexec operation is aborted to prevent proceeding
> with an inconsistent state. An error is returned to user.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> kernel/kexec_core.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index a8890dd03a1d..3122235c225b 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -15,6 +15,7 @@
> #include <linux/kexec.h>
> #include <linux/mutex.h>
> #include <linux/list.h>
> +#include <linux/liveupdate.h>
> #include <linux/highmem.h>
> #include <linux/syscalls.h>
> #include <linux/reboot.h>
> @@ -1145,6 +1146,10 @@ int kernel_kexec(void)
> goto Unlock;
> }
>
> + error = liveupdate_reboot();
> + if (error)
> + goto Unlock;
> +
> #ifdef CONFIG_KEXEC_JUMP
> if (kexec_image->preserve_context) {
> /*
> --
> 2.52.0.rc1.455.g30608eb744-goog
>
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 02/20] liveupdate: luo_core: integrate with KHO
From: Pasha Tatashin @ 2025-11-16 14:55 UTC (permalink / raw)
To: Mike Rapoport
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <aRnG8wDSSAtkEI_z@kernel.org>
On Sun, Nov 16, 2025 at 7:43 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Sat, Nov 15, 2025 at 06:33:48PM -0500, Pasha Tatashin wrote:
> > Integrate the LUO with the KHO framework to enable passing LUO state
> > across a kexec reboot.
> >
> > When LUO is transitioned to a "prepared" state, it tells KHO to
> > finalize, so all memory segments that were added to KHO preservation
> > list are getting preserved. After "Prepared" state no new segments
> > can be preserved. If LUO is canceled, it also tells KHO to cancel the
> > serialization, and therefore, later LUO can go back into the prepared
> > state.
> >
> > This patch introduces the following changes:
> > - During the KHO finalization phase allocate FDT blob.
>
> This happens much earlier, isn't it?
It is, this commit log needs to be updated, it still talks about
prepare/cancel, where they are since v5 replaced with
preserve/unfreeze.
>
> > - Populate this FDT with a LUO compatibility string ("luo-v1").
> >
> > LUO now depends on `CONFIG_KEXEC_HANDOVER`. The core state transition
> > logic (`luo_do_*_calls`) remains unimplemented in this patch.
> >
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > ---
> > include/linux/liveupdate/abi/luo.h | 54 ++++++++++
> > kernel/liveupdate/luo_core.c | 153 ++++++++++++++++++++++++++++-
> > 2 files changed, 206 insertions(+), 1 deletion(-)
> > create mode 100644 include/linux/liveupdate/abi/luo.h
> >
> > diff --git a/include/linux/liveupdate/abi/luo.h b/include/linux/liveupdate/abi/luo.h
> > new file mode 100644
> > index 000000000000..9483a294287f
> > --- /dev/null
> > +++ b/include/linux/liveupdate/abi/luo.h
> > @@ -0,0 +1,54 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +
> > +/*
> > + * Copyright (c) 2025, Google LLC.
> > + * Pasha Tatashin <pasha.tatashin@soleen.com>
> > + */
> > +
> > +/**
> > + * DOC: Live Update Orchestrator ABI
> > + *
> > + * This header defines the stable Application Binary Interface used by the
> > + * Live Update Orchestrator to pass state from a pre-update kernel to a
> > + * post-update kernel. The ABI is built upon the Kexec HandOver framework
> > + * and uses a Flattened Device Tree to describe the preserved data.
> > + *
> > + * This interface is a contract. Any modification to the FDT structure, node
> > + * properties, compatible strings, or the layout of the `__packed` serialization
> > + * structures defined here constitutes a breaking change. Such changes require
> > + * incrementing the version number in the relevant `_COMPATIBLE` string to
> > + * prevent a new kernel from misinterpreting data from an old kernel.
>
> I'd add a sentence that stresses that ABI changes are possible as long they
> include changes to the FDT version.
> This is indeed implied by the last paragraph, but I think it's worth
> spelling it explicitly.
>
> Another thing that I think this should mention is that compatibility is
> only guaranteed for the kernels that use the same ABI version.
Sure, I will add both.
> > + *
> > + * FDT Structure Overview:
> > + * The entire LUO state is encapsulated within a single KHO entry named "LUO".
> > + * This entry contains an FDT with the following layout:
> > + *
> > + * .. code-block:: none
> > + *
> > + * / {
> > + * compatible = "luo-v1";
> > + * liveupdate-number = <...>;
> > + * };
> > + *
> > + * Main LUO Node (/):
> > + *
> > + * - compatible: "luo-v1"
> > + * Identifies the overall LUO ABI version.
> > + * - liveupdate-number: u64
> > + * A counter tracking the number of successful live updates performed.
> > + */
> ...
>
> > +static int __init liveupdate_early_init(void)
> > +{
> > + int err;
> > +
> > + err = luo_early_startup();
> > + if (err) {
> > + pr_err("The incoming tree failed to initialize properly [%pe], disabling live update\n",
> > + ERR_PTR(err));
>
> How do we report this to the userspace?
> I think the decision what to do in this case belongs there. Even if it's
> down to choosing between plain kexec and full reboot, it's still a policy
> that should be implemented in userspace.
I agree that policy belongs in userspace, and that is how we designed
it. In this specific failure case (ABI mismatch or corrupt FDT), the
preserved state is unrecoverable by the kernel. We cannot parse the
incoming data, so we cannot offer it to userspace.
We report this state by not registering the /dev/liveupdate device.
When the userspace agent attempts to initialize, it receives ENOENT.
At that point, the agent exercises its policy:
- Check dmesg for the specific error and report the failure to the
fleet control plane.
- Trigger a fresh (kexec or cold) reboot to reset unreclaimable resources.
Pasha
^ permalink raw reply
* Re: [PATCH v6 04/20] liveupdate: luo_session: add sessions support
From: Mike Rapoport @ 2025-11-16 17:05 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-5-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:50PM -0500, Pasha Tatashin wrote:
> Introduce concept of "Live Update Sessions" within the LUO framework.
> LUO sessions provide a mechanism to group and manage `struct file *`
> instances (representing file descriptors) that need to be preserved
> across a kexec-based live update.
>
> Each session is identified by a unique name and acts as a container
> for file objects whose state is critical to a userspace workload, such
> as a virtual machine or a high-performance database, aiming to maintain
> their functionality across a kernel transition.
>
> This groundwork establishes the framework for preserving file-backed
> state across kernel updates, with the actual file data preservation
> mechanisms to be implemented in subsequent patches.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/linux/liveupdate/abi/luo.h | 83 +++++-
> include/uapi/linux/liveupdate.h | 3 +
> kernel/liveupdate/Makefile | 3 +-
> kernel/liveupdate/luo_core.c | 10 +
> kernel/liveupdate/luo_internal.h | 52 ++++
> kernel/liveupdate/luo_session.c | 421 +++++++++++++++++++++++++++++
> 6 files changed, 570 insertions(+), 2 deletions(-)
> create mode 100644 kernel/liveupdate/luo_internal.h
> create mode 100644 kernel/liveupdate/luo_session.c
...
> +/**
> + * struct luo_session_ser - Represents the serialized metadata for a LUO session.
> + * @name: The unique name of the session, copied from the `luo_session`
> + * structure.
I'd phase it as
The unique name of the session provided by the userspace at
the time of session creation.
> + * @files: The physical address of a contiguous memory block that holds
> + * the serialized state of files.
Maybe add ^ in this session?
> + * @pgcnt: The number of pages occupied by the `files` memory block.
> + * @count: The total number of files that were part of this session during
> + * serialization. Used for iteration and validation during
> + * restoration.
> + *
> + * This structure is used to package session-specific metadata for transfer
> + * between kernels via Kexec Handover. An array of these structures (one per
> + * session) is created and passed to the new kernel, allowing it to reconstruct
> + * the session context.
> + *
> + * If this structure is modified, LUO_SESSION_COMPATIBLE must be updated.
This comment applies to the luo_session_header_ser description as well.
> + */
> +struct luo_session_ser {
> + char name[LIVEUPDATE_SESSION_NAME_LENGTH];
> + u64 files;
> + u64 pgcnt;
> + u64 count;
> +} __packed;
> +
> #endif /* _LINUX_LIVEUPDATE_ABI_LUO_H */
> diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
> index df34c1642c4d..d2ef2f7e0dbd 100644
> --- a/include/uapi/linux/liveupdate.h
> +++ b/include/uapi/linux/liveupdate.h
> @@ -43,4 +43,7 @@
> /* The ioctl type, documented in ioctl-number.rst */
> #define LIVEUPDATE_IOCTL_TYPE 0xBA
>
> +/* The maximum length of session name including null termination */
> +#define LIVEUPDATE_SESSION_NAME_LENGTH 56
You decided not to bump it to 64 in the end? ;-)
> +
> #endif /* _UAPI_LIVEUPDATE_H */
> diff --git a/kernel/liveupdate/Makefile b/kernel/liveupdate/Makefile
> index 413722002b7a..83285e7ad726 100644
> --- a/kernel/liveupdate/Makefile
> +++ b/kernel/liveupdate/Makefile
> @@ -2,7 +2,8 @@
>
> luo-y := \
> luo_core.o \
> - luo_ioctl.o
> + luo_ioctl.o \
> + luo_session.o
>
> obj-$(CONFIG_KEXEC_HANDOVER) += kexec_handover.o
> obj-$(CONFIG_KEXEC_HANDOVER_DEBUG) += kexec_handover_debug.o
...
> +int luo_session_retrieve(const char *name, struct file **filep)
> +{
> + struct luo_session_header *sh = &luo_session_global.incoming;
> + struct luo_session *session = NULL;
> + struct luo_session *it;
> + int err;
> +
> + scoped_guard(rwsem_read, &sh->rwsem) {
> + list_for_each_entry(it, &sh->list, list) {
> + if (!strncmp(it->name, name, sizeof(it->name))) {
> + session = it;
> + break;
> + }
> + }
> + }
> +
> + if (!session)
> + return -ENOENT;
> +
> + scoped_guard(mutex, &session->mutex) {
> + if (session->retrieved)
> + return -EINVAL;
> + }
> +
> + err = luo_session_getfile(session, filep);
> + if (!err) {
> + scoped_guard(mutex, &session->mutex)
> + session->retrieved = true;
Retaking the mutex here seems a bit odd.
Do we really have to lock session->mutex in luo_session_getfile()?
> + }
> +
> + return err;
> +}
...
> +int __init luo_session_setup_incoming(void *fdt_in)
> +{
> + struct luo_session_header_ser *header_ser;
> + int err, header_size, offset;
> + u64 header_ser_pa;
> + const void *ptr;
> +
> + offset = fdt_subnode_offset(fdt_in, 0, LUO_FDT_SESSION_NODE_NAME);
> + if (offset < 0) {
> + pr_err("Unable to get session node: [%s]\n",
> + LUO_FDT_SESSION_NODE_NAME);
> + return -EINVAL;
> + }
> +
> + err = fdt_node_check_compatible(fdt_in, offset,
> + LUO_FDT_SESSION_COMPATIBLE);
> + if (err) {
> + pr_err("Session node incompatible [%s]\n",
> + LUO_FDT_SESSION_COMPATIBLE);
> + return -EINVAL;
> + }
> +
> + header_size = 0;
> + ptr = fdt_getprop(fdt_in, offset, LUO_FDT_SESSION_HEADER, &header_size);
> + if (!ptr || header_size != sizeof(u64)) {
> + pr_err("Unable to get session header '%s' [%d]\n",
> + LUO_FDT_SESSION_HEADER, header_size);
> + return -EINVAL;
> + }
> +
> + header_ser_pa = get_unaligned((u64 *)ptr);
> + header_ser = phys_to_virt(header_ser_pa);
> +
> + luo_session_global.incoming.header_ser = header_ser;
> + luo_session_global.incoming.ser = (void *)(header_ser + 1);
> + INIT_LIST_HEAD(&luo_session_global.incoming.list);
> + init_rwsem(&luo_session_global.incoming.rwsem);
> + luo_session_global.incoming.active = true;
> +
> + return 0;
> +}
> +
> +bool luo_session_is_deserialized(void)
> +{
> + return luo_session_global.deserialized;
> +}
> +
> +int luo_session_deserialize(void)
> +{
> + struct luo_session_header *sh = &luo_session_global.incoming;
> + int err;
> +
> + if (luo_session_is_deserialized())
> + return 0;
> +
> + luo_session_global.deserialized = true;
> + if (!sh->active) {
> + INIT_LIST_HEAD(&sh->list);
> + init_rwsem(&sh->rwsem);
> + return 0;
How this can happen? luo_session_deserialize() is supposed to be called
from ioctl and luo_session_global.incoming should be set up way earlier.
And, why don't we initialize ->list and ->rwsem statically?
> + }
> +
> + for (int i = 0; i < sh->header_ser->count; i++) {
> + struct luo_session *session;
> +
> + session = luo_session_alloc(sh->ser[i].name);
> + if (IS_ERR(session)) {
> + pr_warn("Failed to allocate session [%s] during deserialization %pe\n",
> + sh->ser[i].name, session);
> + return PTR_ERR(session);
> + }
The allocated sessions still need to be freed if an insert fails ;-)
> +
> + err = luo_session_insert(sh, session);
> + if (err) {
> + luo_session_free(session);
> + pr_warn("Failed to insert session [%s] %pe\n",
> + session->name, ERR_PTR(err));
> + return err;
> + }
> +
> + session->count = sh->ser[i].count;
> + session->files = sh->ser[i].files ? phys_to_virt(sh->ser[i].files) : 0;
> + session->pgcnt = sh->ser[i].pgcnt;
> + }
> +
> + kho_restore_free(sh->header_ser);
> + sh->header_ser = NULL;
> + sh->ser = NULL;
> +
> + return 0;
> +}
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 05/20] liveupdate: luo_ioctl: add user interface
From: Mike Rapoport @ 2025-11-16 17:15 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-6-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:51PM -0500, Pasha Tatashin wrote:
> Introduce the user-space interface for the Live Update Orchestrator
> via ioctl commands, enabling external control over the live update
> process and management of preserved resources.
>
> The idea is that there is going to be a single userspace agent driving
> the live update, therefore, only a single process can ever hold this
> device opened at a time.
>
> The following ioctl commands are introduced:
>
> LIVEUPDATE_IOCTL_CREATE_SESSION
> Provides a way for userspace to create a named session for grouping file
> descriptors that need to be preserved. It returns a new file descriptor
> representing the session.
>
> LIVEUPDATE_IOCTL_RETRIEVE_SESSION
> Allows the userspace agent in the new kernel to reclaim a preserved
> session by its name, receiving a new file descriptor to manage the
> restored resources.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/uapi/linux/liveupdate.h | 66 +++++++++++-
> kernel/liveupdate/luo_internal.h | 21 ++++
> kernel/liveupdate/luo_ioctl.c | 178 +++++++++++++++++++++++++++++++
> 3 files changed, 264 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
> index d2ef2f7e0dbd..6e04254ee535 100644
> --- a/include/uapi/linux/liveupdate.h
> +++ b/include/uapi/linux/liveupdate.h
> @@ -44,6 +44,70 @@
> #define LIVEUPDATE_IOCTL_TYPE 0xBA
>
> /* The maximum length of session name including null termination */
> -#define LIVEUPDATE_SESSION_NAME_LENGTH 56
> +#define LIVEUPDATE_SESSION_NAME_LENGTH 64
> +
> +/* The /dev/liveupdate ioctl commands */
> +enum {
> + LIVEUPDATE_CMD_BASE = 0x00,
> + LIVEUPDATE_CMD_CREATE_SESSION = LIVEUPDATE_CMD_BASE,
> + LIVEUPDATE_CMD_RETRIEVE_SESSION = 0x01,
> +};
> +
> +/**
> + * struct liveupdate_ioctl_create_session - ioctl(LIVEUPDATE_IOCTL_CREATE_SESSION)
> + * @size: Input; sizeof(struct liveupdate_ioctl_create_session)
> + * @fd: Output; The new file descriptor for the created session.
> + * @name: Input; A null-terminated string for the session name, max
> + * length %LIVEUPDATE_SESSION_NAME_LENGTH including termination
> + * char.
Nit: ^ character
> + *
> + * Creates a new live update session for managing preserved resources.
> + * This ioctl can only be called on the main /dev/liveupdate device.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +struct liveupdate_ioctl_create_session {
> + __u32 size;
> + __s32 fd;
> + __u8 name[LIVEUPDATE_SESSION_NAME_LENGTH];
> +};
> +
> +#define LIVEUPDATE_IOCTL_CREATE_SESSION \
> + _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_CREATE_SESSION)
> +
> +/**
> + * struct liveupdate_ioctl_retrieve_session - ioctl(LIVEUPDATE_IOCTL_RETRIEVE_SESSION)
> + * @size: Input; sizeof(struct liveupdate_ioctl_retrieve_session)
> + * @fd: Output; The new file descriptor for the retrieved session.
> + * @name: Input; A null-terminated string identifying the session to retrieve.
> + * The name must exactly match the name used when the session was
> + * created in the previous kernel.
> + *
> + * Retrieves a handle (a new file descriptor) for a preserved session by its
> + * name. This is the primary mechanism for a userspace agent to regain control
> + * of its preserved resources after a live update.
> + *
> + * The userspace application provides the null-terminated `name` of a session
> + * it created before the live update. If a preserved session with a matching
> + * name is found, the kernel instantiates it and returns a new file descriptor
> + * in the `fd` field. This new session FD can then be used for all file-specific
> + * operations, such as restoring individual file descriptors with
> + * LIVEUPDATE_SESSION_RETRIEVE_FD.
> + *
> + * It is the responsibility of the userspace application to know the names of
> + * the sessions it needs to retrieve. If no session with the given name is
> + * found, the ioctl will fail with -ENOENT.
> + *
> + * This ioctl can only be called on the main /dev/liveupdate device when the
> + * system is in the LIVEUPDATE_STATE_UPDATED state.
> + */
> +struct liveupdate_ioctl_retrieve_session {
> + __u32 size;
> + __s32 fd;
> + __u8 name[LIVEUPDATE_SESSION_NAME_LENGTH];
> +};
> +
> +#define LIVEUPDATE_IOCTL_RETRIEVE_SESSION \
> + _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_RETRIEVE_SESSION)
>
> #endif /* _UAPI_LIVEUPDATE_H */
> diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
> index 245373edfa6f..5185ad37a8c1 100644
> --- a/kernel/liveupdate/luo_internal.h
> +++ b/kernel/liveupdate/luo_internal.h
> @@ -9,6 +9,27 @@
> #define _LINUX_LUO_INTERNAL_H
>
> #include <linux/liveupdate.h>
> +#include <linux/uaccess.h>
> +
> +struct luo_ucmd {
> + void __user *ubuffer;
> + u32 user_size;
> + void *cmd;
> +};
> +
> +static inline int luo_ucmd_respond(struct luo_ucmd *ucmd,
> + size_t kernel_cmd_size)
> +{
> + /*
> + * Copy the minimum of what the user provided and what we actually
> + * have.
> + */
> + if (copy_to_user(ucmd->ubuffer, ucmd->cmd,
> + min_t(size_t, ucmd->user_size, kernel_cmd_size))) {
> + return -EFAULT;
> + }
> + return 0;
> +}
>
> /**
> * struct luo_session - Represents an active or incoming Live Update session.
> diff --git a/kernel/liveupdate/luo_ioctl.c b/kernel/liveupdate/luo_ioctl.c
> index 44d365185f7c..367385efa962 100644
> --- a/kernel/liveupdate/luo_ioctl.c
> +++ b/kernel/liveupdate/luo_ioctl.c
> @@ -5,15 +5,192 @@
> * Pasha Tatashin <pasha.tatashin@soleen.com>
> */
>
> +/**
> + * DOC: LUO ioctl Interface
> + *
> + * The IOCTL user-space control interface for the LUO subsystem.
> + * It registers a character device, typically found at ``/dev/liveupdate``,
> + * which allows a userspace agent to manage the LUO state machine and its
> + * associated resources, such as preservable file descriptors.
> + *
> + * To ensure that the state machine is controlled by a single entity, access
> + * to this device is exclusive: only one process is permitted to have
> + * ``/dev/liveupdate`` open at any given time. Subsequent open attempts will
> + * fail with -EBUSY until the first process closes its file descriptor.
> + * This singleton model simplifies state management by preventing conflicting
> + * commands from multiple userspace agents.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/atomic.h>
> +#include <linux/errno.h>
> +#include <linux/file.h>
> +#include <linux/fs.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> #include <linux/liveupdate.h>
> #include <linux/miscdevice.h>
> +#include <uapi/linux/liveupdate.h>
> +#include "luo_internal.h"
>
> struct luo_device_state {
> struct miscdevice miscdev;
> + atomic_t in_use;
> +};
> +
> +static int luo_ioctl_create_session(struct luo_ucmd *ucmd)
> +{
> + struct liveupdate_ioctl_create_session *argp = ucmd->cmd;
> + struct file *file;
> + int err;
> +
> + argp->fd = get_unused_fd_flags(O_CLOEXEC);
> + if (argp->fd < 0)
> + return argp->fd;
> +
> + err = luo_session_create(argp->name, &file);
> + if (err)
> + goto err_put_fd;
> +
> + err = luo_ucmd_respond(ucmd, sizeof(*argp));
> + if (err)
> + goto err_put_file;
> +
> + fd_install(argp->fd, file);
> +
> + return 0;
> +
> +err_put_file:
> + fput(file);
> +err_put_fd:
> + put_unused_fd(argp->fd);
> +
> + return err;
> +}
> +
> +static int luo_ioctl_retrieve_session(struct luo_ucmd *ucmd)
> +{
> + struct liveupdate_ioctl_retrieve_session *argp = ucmd->cmd;
> + struct file *file;
> + int err;
> +
> + argp->fd = get_unused_fd_flags(O_CLOEXEC);
> + if (argp->fd < 0)
> + return argp->fd;
> +
> + err = luo_session_retrieve(argp->name, &file);
> + if (err < 0)
> + goto err_put_fd;
> +
> + err = luo_ucmd_respond(ucmd, sizeof(*argp));
> + if (err)
> + goto err_put_file;
> +
> + fd_install(argp->fd, file);
> +
> + return 0;
> +
> +err_put_file:
> + fput(file);
> +err_put_fd:
> + put_unused_fd(argp->fd);
> +
> + return err;
> +}
> +
> +static int luo_open(struct inode *inodep, struct file *filep)
> +{
> + struct luo_device_state *ldev = container_of(filep->private_data,
> + struct luo_device_state,
> + miscdev);
> +
> + if (atomic_cmpxchg(&ldev->in_use, 0, 1))
> + return -EBUSY;
> +
> + luo_session_deserialize();
Why luo_session_deserialize() is tied to the first open of the chardev?
> +
> + return 0;
> +}
> +
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 06/20] liveupdate: luo_file: implement file systems callbacks
From: Mike Rapoport @ 2025-11-16 18:15 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-7-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:52PM -0500, Pasha Tatashin wrote:
> This patch implements the core mechanism for managing preserved
> files throughout the live update lifecycle. It provides the logic to
> invoke the file handler callbacks (preserve, unpreserve, freeze,
> unfreeze, retrieve, and finish) at the appropriate stages.
>
> During the reboot phase, luo_file_freeze() serializes the final
> metadata for each file (handler compatible string, token, and data
> handle) into a memory region preserved by KHO. In the new kernel,
> luo_file_deserialize() reconstructs the in-memory file list from this
> data, preparing the session for retrieval.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/linux/liveupdate.h | 109 ++++
> include/linux/liveupdate/abi/luo.h | 22 +
> kernel/liveupdate/Makefile | 1 +
> kernel/liveupdate/luo_file.c | 887 +++++++++++++++++++++++++++++
> kernel/liveupdate/luo_internal.h | 9 +
> 5 files changed, 1028 insertions(+)
> create mode 100644 kernel/liveupdate/luo_file.c
>
> diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
> index 730b76625fec..4a5d4dd9905a 100644
> --- a/include/linux/liveupdate.h
> +++ b/include/linux/liveupdate.h
> @@ -10,6 +10,88 @@
> #include <linux/bug.h>
> #include <linux/types.h>
> #include <linux/list.h>
> +#include <linux/liveupdate/abi/luo.h>
> +#include <uapi/linux/liveupdate.h>
> +
> +struct liveupdate_file_handler;
> +struct liveupdate_session;
Why struct liveupdate_session is a part of public LUO API?
> +struct file;
> +
> +/**
> + * struct liveupdate_file_op_args - Arguments for file operation callbacks.
> + * @handler: The file handler being called.
> + * @session: The session this file belongs to.
> + * @retrieved: The retrieve status for the 'can_finish / finish'
> + * operation.
> + * @file: The file object. For retrieve: [OUT] The callback sets
> + * this to the new file. For other ops: [IN] The caller sets
> + * this to the file being operated on.
> + * @serialized_data: The opaque u64 handle, preserve/prepare/freeze may update
> + * this field.
> + *
> + * This structure bundles all parameters for the file operation callbacks.
> + * The 'data' and 'file' fields are used for both input and output.
> + */
> +struct liveupdate_file_op_args {
> + struct liveupdate_file_handler *handler;
> + struct liveupdate_session *session;
> + bool retrieved;
> + struct file *file;
> + u64 serialized_data;
> +};
> +
> +/**
> + * struct liveupdate_file_ops - Callbacks for live-updatable files.
> + * @can_preserve: Required. Lightweight check to see if this handler is
> + * compatible with the given file.
> + * @preserve: Required. Performs state-saving for the file.
> + * @unpreserve: Required. Cleans up any resources allocated by @preserve.
> + * @freeze: Optional. Final actions just before kernel transition.
> + * @unfreeze: Optional. Undo freeze operations.
> + * @retrieve: Required. Restores the file in the new kernel.
> + * @can_finish: Optional. Check if this FD can finish, i.e. all restoration
> + * pre-requirements for this FD are satisfied. Called prior to
> + * finish, in order to do successful finish calls for all
> + * resources in the session.
> + * @finish: Required. Final cleanup in the new kernel.
> + * @owner: Module reference
> + *
> + * All operations (except can_preserve) receive a pointer to a
> + * 'struct liveupdate_file_op_args' containing the necessary context.
> + */
> +struct liveupdate_file_ops {
> + bool (*can_preserve)(struct liveupdate_file_handler *handler,
> + struct file *file);
> + int (*preserve)(struct liveupdate_file_op_args *args);
> + void (*unpreserve)(struct liveupdate_file_op_args *args);
> + int (*freeze)(struct liveupdate_file_op_args *args);
> + void (*unfreeze)(struct liveupdate_file_op_args *args);
> + int (*retrieve)(struct liveupdate_file_op_args *args);
> + bool (*can_finish)(struct liveupdate_file_op_args *args);
> + void (*finish)(struct liveupdate_file_op_args *args);
> + struct module *owner;
> +};
> +
> +/**
> + * struct liveupdate_file_handler - Represents a handler for a live-updatable file type.
> + * @ops: Callback functions
> + * @compatible: The compatibility string (e.g., "memfd-v1", "vfiofd-v1")
> + * that uniquely identifies the file type this handler
> + * supports. This is matched against the compatible string
> + * associated with individual &struct file instances.
> + * @list: Used for linking this handler instance into a global
> + * list of registered file handlers.
> + *
> + * Modules that want to support live update for specific file types should
> + * register an instance of this structure. LUO uses this registration to
> + * determine if a given file can be preserved and to find the appropriate
> + * operations to manage its state across the update.
> + */
> +struct liveupdate_file_handler {
> + const struct liveupdate_file_ops *ops;
> + const char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
> + struct list_head list;
Did you consider using __private and ACCESS_PRIVATE() for the ->list
member here and in other structures visible outside kernel/liveupdate?
> +};
>
> #ifdef CONFIG_LIVEUPDATE
>
> @@ -19,6 +101,16 @@ bool liveupdate_enabled(void);
> /* Called during kexec to tell LUO that entered into reboot */
> int liveupdate_reboot(void);
>
> +int liveupdate_register_file_handler(struct liveupdate_file_handler *h);
> +
> +/* kernel can internally retrieve files */
> +int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
> + struct file **filep);
> +
> +/* Get a token for an outgoing file, or -ENOENT if file is not preserved */
> +int liveupdate_get_token_outgoing(struct liveupdate_session *s,
> + struct file *file, u64 *tokenp);
> +
> #else /* CONFIG_LIVEUPDATE */
>
> static inline bool liveupdate_enabled(void)
> @@ -31,5 +123,22 @@ static inline int liveupdate_reboot(void)
> return 0;
> }
>
> +static inline int liveupdate_register_file_handler(struct liveupdate_file_handler *h)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> +static inline int liveupdate_get_file_incoming(struct liveupdate_session *s,
> + u64 token, struct file **filep)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> +static inline int liveupdate_get_token_outgoing(struct liveupdate_session *s,
> + struct file *file, u64 *tokenp)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> #endif /* CONFIG_LIVEUPDATE */
> #endif /* _LINUX_LIVEUPDATE_H */
> diff --git a/include/linux/liveupdate/abi/luo.h b/include/linux/liveupdate/abi/luo.h
> index 03a177ae232e..3a596ca1907b 100644
> --- a/include/linux/liveupdate/abi/luo.h
> +++ b/include/linux/liveupdate/abi/luo.h
> @@ -65,6 +65,11 @@
> * Metadata for a single session, including its name and a physical pointer
> * to another preserved memory block containing an array of
> * `struct luo_file_ser` for all files in that session.
> + *
> + * - struct luo_file_ser:
> + * Metadata for a single preserved file. Contains the `compatible` string to
> + * find the correct handler in the new kernel, a user-provided `token` for
> + * identification, and an opaque `data` handle for the handler to use.
> */
>
> #ifndef _LINUX_LIVEUPDATE_ABI_LUO_H
> @@ -132,4 +137,21 @@ struct luo_session_ser {
> u64 count;
> } __packed;
>
> +/* The max size is set so it can be reliably used during in serialization */
I failed to parse this comment.
> +#define LIVEUPDATE_HNDL_COMPAT_LENGTH 48
> +
> +/**
> + * struct luo_file_ser - Represents the serialized preserves files.
> + * @compatible: File handler compatible string.
> + * @data: Private data
> + * @token: User provided token for this file
> + *
> + * If this structure is modified, LUO_SESSION_COMPATIBLE must be updated.
> + */
> +struct luo_file_ser {
> + char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
> + u64 data;
> + u64 token;
> +} __packed;
> +
> #endif /* _LINUX_LIVEUPDATE_ABI_LUO_H */
> diff --git a/kernel/liveupdate/Makefile b/kernel/liveupdate/Makefile
> index 83285e7ad726..c2252a2ad7bd 100644
> --- a/kernel/liveupdate/Makefile
> +++ b/kernel/liveupdate/Makefile
> @@ -2,6 +2,7 @@
>
> luo-y := \
> luo_core.o \
> + luo_file.o \
> luo_ioctl.o \
> luo_session.o
>
> diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> new file mode 100644
> index 000000000000..dae27a69a09f
> --- /dev/null
> +++ b/kernel/liveupdate/luo_file.c
> @@ -0,0 +1,887 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (c) 2025, Google LLC.
> + * Pasha Tatashin <pasha.tatashin@soleen.com>
> + */
> +
> +/**
> + * DOC: LUO File Descriptors
> + *
> + * LUO provides the infrastructure to preserve specific, stateful file
> + * descriptors across a kexec-based live update. The primary goal is to allow
> + * workloads, such as virtual machines using vfio, memfd, or iommufd, to
> + * retain access to their essential resources without interruption.
> + *
> + * The framework is built around a callback-based handler model and a well-
> + * defined lifecycle for each preserved file.
> + *
> + * Handler Registration:
> + * Kernel modules responsible for a specific file type (e.g., memfd, vfio)
> + * register a &struct liveupdate_file_handler. This handler provides a set of
> + * callbacks that LUO invokes at different stages of the update process, most
> + * notably:
> + *
> + * - can_preserve(): A lightweight check to determine if the handler is
> + * compatible with a given 'struct file'.
> + * - preserve(): The heavyweight operation that saves the file's state and
> + * returns an opaque u64 handle, happens while vcpus are still running.
^ VCPUs
This narrows the description to VM-only usecase and in general ->preserve()
may happen after VCPUs are suspended, although it's neither intended nor
desirable. LUO does not control the sequencing so we can't claim here
anything about VCPUs.
> + * LUO becomes the owner of this file until session is closed or file is
> + * finished.
"file is finished" reads too vague to me.
> + * - unpreserve(): Cleans up any resources allocated by .preserve(), called
> + * if the preservation process is aborted before the reboot (i.e. session is
> + * closed).
> + * - freeze(): A final pre-reboot opportunity to prepare the state for kexec.
> + * We are already in reboot syscall, and therefore userspace cannot mutate
> + * the file anymore.
> + * - unfreeze(): Undoes the actions of .freeze(), called if the live update
> + * is aborted after the freeze phase.
> + * - retrieve(): Reconstructs the file in the new kernel from the preserved
> + * handle.
> + * - finish(): Performs final check and cleanup in the new kernel. After
> + * succesul finish call, LUO gives up ownership to this file.
> + *
> + * File Preservation Lifecycle happy path:
> + *
> + * 1. Preserve (Normal Operation): A userspace agent preserves files one by one
> + * via an ioctl. For each file, luo_preserve_file() finds a compatible
> + * handler, calls its .preserve() op, and creates an internal &struct
^ method or operation
> + * luo_file to track the live state.
> + *
> + * 2. Freeze (Pre-Reboot): Just before the kexec, luo_file_freeze() is called.
> + * It iterates through all preserved files, calls their respective .freeze()
> + * ops, and serializes their final metadata (compatible string, token, and
^ method or operation
> + * data handle) into a contiguous memory block for KHO.
> + *
> + * 3. Deserialize (New Kernel - Early Boot): After kexec, luo_file_deserialize()
From the code it seems that description runs on the fist open of
/dev/liveupdated, what do I miss?
> + * runs. It reads the serialized data from the KHO memory region and
> + * reconstructs the in-memory list of &struct luo_file instances for the new
> + * kernel, linking them to their corresponding handlers.
> + *
> + * 4. Retrieve (New Kernel - Userspace Ready): The userspace agent can now
> + * restore file descriptors by providing a token. luo_retrieve_file()
> + * searches for the matching token, calls the handler's .retrieve() op to
> + * re-create the 'struct file', and returns a new FD. Files can be
> + * retrieved in ANY order.
> + *
> + * 5. Finish (New Kernel - Cleanup): Once a session retrival is complete,
> + * luo_file_finish() is called. It iterates through all files,
> + * invokes their .finish() ops for final cleanup, and releases all
^ method
> + * associated kernel resources.
> + *
> + * File Preservation Lifecycle unhappy paths:
> + *
> + * 1. Abort Before Reboot: If the userspace agent aborts the live update
> + * process before calling reboot (e.g., by closing the session file
> + * descriptor), the session's release handler calls
> + * luo_file_unpreserve_files(). This invokes the .unpreserve() callback on
> + * all preserved files, ensuring all allocated resources are cleaned up and
> + * returning the system to a clean state.
> + *
> + * 2. Freeze Failure: During the reboot() syscall, if any handler's .freeze()
> + * op fails, the .unfreeze() op is invoked on all previously *successful*
> + * freezes to roll back their state. The reboot() syscall then returns an
> + * error to userspace, canceling the live update.
> + *
> + * 3. Finish Failure: In the new kernel, if a handler's .finish() op fails,
> + * the luo_file_finish() operation is aborted. LUO retains ownership of
> + * all files within that session, including those that were not yet
> + * processed. The userspace agent can attempt to call the finish operation
> + * again later. If the issue cannot be resolved, these resources will be held
> + * by LUO until the next live update cycle, at which point they will be
> + * discarded.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/cleanup.h>
> +#include <linux/err.h>
> +#include <linux/errno.h>
> +#include <linux/file.h>
> +#include <linux/fs.h>
> +#include <linux/kexec_handover.h>
> +#include <linux/liveupdate.h>
> +#include <linux/liveupdate/abi/luo.h>
> +#include <linux/module.h>
> +#include <linux/sizes.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +#include "luo_internal.h"
> +
> +static LIST_HEAD(luo_file_handler_list);
> +
> +/* 2 4K pages, give space for 128 files per session */
> +#define LUO_FILE_PGCNT 2ul
> +#define LUO_FILE_MAX \
> + ((LUO_FILE_PGCNT << PAGE_SHIFT) / sizeof(struct luo_file_ser))
> +
> +/**
> + * struct luo_file - Represents a single preserved file instance.
> + * @fh: Pointer to the &struct liveupdate_file_handler that manages
> + * this type of file.
> + * @file: Pointer to the kernel's &struct file that is being preserved.
> + * This is NULL in the new kernel until the file is successfully
> + * retrieved.
> + * @serialized_data: The opaque u64 handle to the serialized state of the file.
> + * This handle is passed back to the handler's .freeze(),
> + * .retrieve(), and .finish() callbacks, allowing it to track
> + * and update its serialized state across phases.
> + * @retrieved: A flag indicating whether a user/kernel in the new kernel has
> + * successfully called retrieve() on this file. This prevents
> + * multiple retrieval attempts.
> + * @mutex: A mutex that protects the fields of this specific instance
> + * (e.g., @retrieved, @file), ensuring that operations like
> + * retrieving or finishing a file are atomic.
> + * @list: The list_head linking this instance into its parent
> + * session's list of preserved files.
> + * @token: The user-provided unique token used to identify this file.
> + *
> + * This structure is the core in-kernel representation of a single file being
> + * managed through a live update. An instance is created by luo_preserve_file()
> + * to link a 'struct file' to its corresponding handler, a user-provided token,
> + * and the serialized state handle returned by the handler's .preserve()
> + * operation.
> + *
> + * These instances are tracked in a per-session list. The @serialized_data
> + * field, which holds a handle to the file's serialized state, may be updated
> + * during the .freeze() callback before being serialized for the next kernel.
> + * After reboot, these structures are recreated by luo_file_deserialize() and
> + * are finally cleaned up by luo_file_finish().
> + */
> +struct luo_file {
> + struct liveupdate_file_handler *fh;
> + struct file *file;
> + u64 serialized_data;
> + bool retrieved;
> + struct mutex mutex;
> + struct list_head list;
> + u64 token;
> +};
> +
> +static int luo_session_alloc_files_mem(struct luo_session *session)
It seems like this belongs to luo_session.c
> +{
> + size_t size;
> + void *mem;
> +
> + if (session->files)
> + return 0;
> +
> + WARN_ON_ONCE(session->count);
> +
> + size = LUO_FILE_PGCNT << PAGE_SHIFT;
> + mem = kho_alloc_preserve(size);
> + if (IS_ERR(mem))
> + return PTR_ERR(mem);
> +
> + session->files = mem;
> + session->pgcnt = LUO_FILE_PGCNT;
> +
> + return 0;
> +}
> +
> +static void luo_session_free_files_mem(struct luo_session *session)
> +{
Ditto
> + /* If session has files, no need to free preservation memory */
> + if (session->count)
> + return;
> +
> + if (!session->files)
> + return;
> +
> + kho_unpreserve_free(session->files);
> + session->files = NULL;
> + session->pgcnt = 0;
> +}
> +
> +static bool luo_token_is_used(struct luo_session *session, u64 token)
> +{
> + struct luo_file *iter;
> +
> + list_for_each_entry(iter, &session->files_list, list) {
And here again I'm not very fond of dereferencing session objects in
luo_file.
> + if (iter->token == token)
> + return true;
> + }
> +
> + return false;
> +}
> +
> +/**
> + * luo_preserve_file - Initiate the preservation of a file descriptor.
> + * @session: The session to which the preserved file will be added.
> + * @token: A unique, user-provided identifier for the file.
> + * @fd: The file descriptor to be preserved.
> + *
> + * This function orchestrates the first phase of preserving a file. Upon entry,
> + * it takes a reference to the 'struct file' via fget(), effectively making LUO
> + * a co-owner of the file. This reference is held until the file is either
> + * unpreserved or successfully finished in the next kernel, preventing the file
> + * from being prematurely destroyed.
> + *
> + * This function orchestrates the first phase of preserving a file. It performs
> + * the following steps:
> + *
> + * 1. Validates that the @token is not already in use within the session.
> + * 2. Ensures the session's memory for files serialization is allocated
> + * (allocates if needed).
> + * 3. Iterates through registered handlers, calling can_preserve() to find one
> + * compatible with the given @fd.
> + * 4. Calls the handler's .preserve() operation, which saves the file's state
> + * and returns an opaque private data handle.
> + * 5. Adds the new instance to the session's internal list.
> + *
> + * On success, LUO takes a reference to the 'struct file' and considers it
> + * under its management until it is unpreserved or finished.
> + *
> + * In case of any failure, all intermediate allocations (file reference, memory
> + * for the 'luo_file' struct, etc.) are cleaned up before returning an error.
> + *
> + * Context: Can be called from an ioctl handler during normal system operation.
> + * Return: 0 on success. Returns a negative errno on failure:
> + * -EEXIST if the token is already used.
> + * -EBADF if the file descriptor is invalid.
> + * -ENOSPC if the session is full.
> + * -ENOENT if no compatible handler is found.
> + * -ENOMEM on memory allocation failure.
> + * Other erros might be returned by .preserve().
> + */
> +int luo_preserve_file(struct luo_session *session, u64 token, int fd)
> +{
> + struct liveupdate_file_op_args args = {0};
> + struct liveupdate_file_handler *fh;
> + struct luo_file *luo_file;
> + struct file *file;
> + int err;
> +
> + lockdep_assert_held(&session->mutex);
> +
> + if (luo_token_is_used(session, token))
> + return -EEXIST;
> +
> + file = fget(fd);
> + if (!file)
> + return -EBADF;
> +
> + err = luo_session_alloc_files_mem(session);
> + if (err)
> + goto exit_err;
> +
> + if (session->count == LUO_FILE_MAX) {
> + err = -ENOSPC;
> + goto exit_err;
> + }
I believe session can be prepared and vailidated by the caller.
> +
> + err = -ENOENT;
> + list_for_each_entry(fh, &luo_file_handler_list, list) {
> + if (fh->ops->can_preserve(fh, file)) {
> + err = 0;
> + break;
> + }
> + }
> +
> + /* err is still -ENOENT if no handler was found */
> + if (err)
> + goto exit_err;
> +
> + luo_file = kzalloc(sizeof(*luo_file), GFP_KERNEL);
> + if (!luo_file) {
> + err = -ENOMEM;
> + goto exit_err;
> + }
> +
> + luo_file->file = file;
> + luo_file->fh = fh;
> + luo_file->token = token;
> + luo_file->retrieved = false;
> + mutex_init(&luo_file->mutex);
> +
> + args.handler = fh;
> + args.session = (struct liveupdate_session *)session;
Isn't args.session already struct liveupdate_session *?
> + args.file = file;
> + err = fh->ops->preserve(&args);
> + if (err) {
> + mutex_destroy(&luo_file->mutex);
> + kfree(luo_file);
> + goto exit_err;
> + } else {
> + luo_file->serialized_data = args.serialized_data;
> + list_add_tail(&luo_file->list, &session->files_list);
> + session->count++;
I'd use luo_session_add_file(struct luo_file *luo_file) or return luo_file
by reference to the caller.
Than the lockdep_assert_held() can go away as well.
> + }
> +
> + return 0;
> +
> +exit_err:
> + fput(file);
> + luo_session_free_files_mem(session);
The error handling in this function is a mess. Pasha, please, please, use
goto consistently.
> +
> + return err;
> +}
> +
> +/**
> + * luo_file_unpreserve_files - Unpreserves all files from a session.
> + * @session: The session to be cleaned up.
> + *
> + * This function serves as the primary cleanup path for a session. It is
> + * invoked when the userspace agent closes the session's file descriptor.
> + *
> + * For each file, it performs the following cleanup actions:
> + * 1. Calls the handler's .unpreserve() callback to allow the handler to
> + * release any resources it allocated.
> + * 2. Removes the file from the session's internal tracking list.
> + * 3. Releases the reference to the 'struct file' that was taken by
> + * luo_preserve_file() via fput(), returning ownership.
> + * 4. Frees the memory associated with the internal 'struct luo_file'.
> + *
> + * After all individual files are unpreserved, it frees the contiguous memory
> + * block that was allocated to hold their serialization data.
> + */
> +void luo_file_unpreserve_files(struct luo_session *session)
> +{
> + struct luo_file *luo_file;
> +
> + lockdep_assert_held(&session->mutex);
> +
> + while (!list_empty(&session->files_list)) {
I think the loop should be in luo_session.c and luo_files.c should
implement luo_file_unpreserve(struct luo_file *luo_file)
The same applies to other functions below that do something with all files
in the session. In my view luo_session should iterate through
luo_session.files_list and call luo_file methods for each luo_file object.
> + struct liveupdate_file_op_args args = {0};
> +
> + luo_file = list_last_entry(&session->files_list,
> + struct luo_file, list);
> +
> + args.handler = luo_file->fh;
> + args.session = (struct liveupdate_session *)session;
> + args.file = luo_file->file;
> + args.serialized_data = luo_file->serialized_data;
> + luo_file->fh->ops->unpreserve(&args);
> +
> + list_del(&luo_file->list);
> + session->count--;
> +
> + fput(luo_file->file);
> + mutex_destroy(&luo_file->mutex);
> + kfree(luo_file);
> + }
> +
> + luo_session_free_files_mem(session);
> +}
> +
> +static int luo_file_freeze_one(struct luo_session *session,
> + struct luo_file *luo_file)
> +{
> + int err = 0;
> +
> + guard(mutex)(&luo_file->mutex);
> +
> + if (luo_file->fh->ops->freeze) {
> + struct liveupdate_file_op_args args = {0};
> +
> + args.handler = luo_file->fh;
> + args.session = (struct liveupdate_session *)session;
> + args.file = luo_file->file;
> + args.serialized_data = luo_file->serialized_data;
> +
> + err = luo_file->fh->ops->freeze(&args);
> + if (!err)
> + luo_file->serialized_data = args.serialized_data;
> + }
> +
> + return err;
> +}
> +
> +static void luo_file_unfreeze_one(struct luo_session *session,
> + struct luo_file *luo_file)
> +{
> + guard(mutex)(&luo_file->mutex);
> +
> + if (luo_file->fh->ops->unfreeze) {
> + struct liveupdate_file_op_args args = {0};
> +
> + args.handler = luo_file->fh;
> + args.session = (struct liveupdate_session *)session;
> + args.file = luo_file->file;
> + args.serialized_data = luo_file->serialized_data;
> +
> + luo_file->fh->ops->unfreeze(&args);
> + }
> +
> + luo_file->serialized_data = 0;
> +}
> +
> +static void __luo_file_unfreeze(struct luo_session *session,
> + struct luo_file *failed_entry)
> +{
> + struct list_head *files_list = &session->files_list;
> + struct luo_file *luo_file;
> +
> + list_for_each_entry(luo_file, files_list, list) {
> + if (luo_file == failed_entry)
> + break;
> +
> + luo_file_unfreeze_one(session, luo_file);
> + }
> +
> + memset(session->files, 0, session->pgcnt << PAGE_SHIFT);
> +}
> +
> +/**
> + * luo_file_freeze - Freezes all preserved files and serializes their metadata.
> + * @session: The session whose files are to be frozen.
> + *
> + * This function is called from the reboot() syscall path, just before the
> + * kernel transitions to the new image via kexec. Its purpose is to perform the
> + * final preparation and serialization of all preserved files in the session.
> + *
> + * It iterates through each preserved file in FIFO order (the order of
> + * preservation) and performs two main actions:
> + *
> + * 1. Freezes the File: It calls the handler's .freeze() callback for each
> + * file. This gives the handler a final opportunity to quiesce the device or
> + * prepare its state for the upcoming reboot. The handler may update its
> + * private data handle during this step.
> + *
> + * 2. Serializes Metadata: After a successful freeze, it copies the final file
> + * metadata—the handler's compatible string, the user token, and the final
> + * private data handle—into the pre-allocated contiguous memory buffer
> + * (session->files) that will be handed over to the next kernel via KHO.
> + *
> + * Error Handling (Rollback):
> + * This function is atomic. If any handler's .freeze() operation fails, the
> + * entire live update is aborted. The __luo_file_unfreeze() helper is
> + * immediately called to invoke the .unfreeze() op on all files that were
> + * successfully frozen before the point of failure, rolling them back to a
> + * running state. The function then returns an error, causing the reboot()
> + * syscall to fail.
> + *
> + * Context: Called only from the liveupdate_reboot() path.
> + * Return: 0 on success, or a negative errno on failure.
> + */
> +int luo_file_freeze(struct luo_session *session)
> +{
> + struct luo_file_ser *file_ser = session->files;
> + struct luo_file *luo_file;
> + int err;
> + int i;
> +
> + lockdep_assert_held(&session->mutex);
> +
> + if (!session->count)
> + return 0;
> +
> + if (WARN_ON(!file_ser))
> + return -EINVAL;
> +
> + i = 0;
> + list_for_each_entry(luo_file, &session->files_list, list) {
> + err = luo_file_freeze_one(session, luo_file);
> + if (err < 0) {
> + pr_warn("Freeze failed for session[%s] token[%#0llx] handler[%s] err[%pe]\n",
> + session->name, luo_file->token,
> + luo_file->fh->compatible, ERR_PTR(err));
> + goto exit_err;
> + }
> +
> + strscpy(file_ser[i].compatible, luo_file->fh->compatible,
> + sizeof(file_ser[i].compatible));
> + file_ser[i].data = luo_file->serialized_data;
> + file_ser[i].token = luo_file->token;
> + i++;
> + }
> +
> + return 0;
> +
> +exit_err:
> + __luo_file_unfreeze(session, luo_file);
Maybe move frozen files to a local list, call __luo_file_unfreeze() with
that list and than splice it back to session.files_list?
> +
> + return err;
> +}
> +
> +/**
> + * luo_file_unfreeze - Unfreezes all files in a session.
> + * @session: The session whose files are to be unfrozen.
> + *
> + * This function rolls back the state of all files in a session after the freeze
> + * phase has begun but must be aborted. It is the counterpart to
> + * luo_file_freeze().
> + *
> + * It invokes the __luo_file_unfreeze() helper with a NULL argument, which
> + * signals the helper to iterate through all files in the session and call
> + * their respective .unfreeze() handler callbacks.
> + *
> + * Context: This is called when the live update is aborted during
> + * the reboot() syscall, after luo_file_freeze() has been called.
> + */
> +void luo_file_unfreeze(struct luo_session *session)
> +{
> + lockdep_assert_held(&session->mutex);
> +
> + if (!session->count)
> + return;
> +
> + __luo_file_unfreeze(session, NULL);
> +}
> +
> +/**
> + * luo_retrieve_file - Restores a preserved file from a session by its token.
> + * @session: The session from which to retrieve the file.
> + * @token: The unique token identifying the file to be restored.
> + * @filep: Output parameter; on success, this is populated with a pointer
> + * to the newly retrieved 'struct file'.
> + *
> + * This function is the primary mechanism for recreating a file in the new
> + * kernel after a live update. It searches the session's list of deserialized
> + * files for an entry matching the provided @token.
> + *
> + * The operation is idempotent: if a file has already been successfully
> + * retrieved, this function will simply return a pointer to the existing
> + * 'struct file' and report success without re-executing the retrieve
> + * operation. This is handled by checking the 'retrieved' flag under a lock.
> + *
> + * File retrieval can happen in any order; it is not bound by the order of
> + * preservation.
> + *
> + * Context: Can be called from an ioctl or other in-kernel code in the new
> + * kernel.
> + * Return: 0 on success. Returns a negative errno on failure:
> + * -ENOENT if no file with the matching token is found.
> + * Any error code returned by the handler's .retrieve() op.
> + */
> +int luo_retrieve_file(struct luo_session *session, u64 token,
> + struct file **filep)
> +{
> + struct liveupdate_file_op_args args = {0};
> + struct luo_file *luo_file;
> + int err;
> +
> + lockdep_assert_held(&session->mutex);
> +
> + if (list_empty(&session->files_list))
> + return -ENOENT;
> +
> + list_for_each_entry(luo_file, &session->files_list, list) {
> + if (luo_file->token == token)
> + break;
> + }
> +
> + if (luo_file->token != token)
> + return -ENOENT;
> +
> + guard(mutex)(&luo_file->mutex);
> + if (luo_file->retrieved) {
> + /*
> + * Someone is asking for this file again, so get a reference
> + * for them.
> + */
> + get_file(luo_file->file);
> + *filep = luo_file->file;
> + return 0;
> + }
> +
> + args.handler = luo_file->fh;
> + args.session = (struct liveupdate_session *)session;
> + args.serialized_data = luo_file->serialized_data;
> + err = luo_file->fh->ops->retrieve(&args);
> + if (!err) {
> + luo_file->file = args.file;
> +
> + /* Get reference so we can keep this file in LUO until finish */
> + get_file(luo_file->file);
> + *filep = luo_file->file;
> + luo_file->retrieved = true;
> + }
> +
> + return err;
> +}
> +
> +static int luo_file_can_finish_one(struct luo_session *session,
> + struct luo_file *luo_file)
> +{
> + bool can_finish = true;
> +
> + guard(mutex)(&luo_file->mutex);
> +
> + if (luo_file->fh->ops->can_finish) {
> + struct liveupdate_file_op_args args = {0};
> +
> + args.handler = luo_file->fh;
> + args.session = (struct liveupdate_session *)session;
> + args.file = luo_file->file;
> + args.serialized_data = luo_file->serialized_data;
> + args.retrieved = luo_file->retrieved;
> + can_finish = luo_file->fh->ops->can_finish(&args);
> + }
> +
> + return can_finish ? 0 : -EBUSY;
> +}
> +
> +static void luo_file_finish_one(struct luo_session *session,
> + struct luo_file *luo_file)
> +{
> + struct liveupdate_file_op_args args = {0};
> +
> + guard(mutex)(&luo_file->mutex);
> +
> + args.handler = luo_file->fh;
> + args.session = (struct liveupdate_session *)session;
> + args.file = luo_file->file;
> + args.serialized_data = luo_file->serialized_data;
> + args.retrieved = luo_file->retrieved;
> +
> + luo_file->fh->ops->finish(&args);
> +}
> +
> +/**
> + * luo_file_finish - Completes the lifecycle for all files in a session.
> + * @session: The session to be finalized.
> + *
> + * This function orchestrates the final teardown of a live update session in the
> + * new kernel. It should be called after all necessary files have been
> + * retrieved and the userspace agent is ready to release the preserved state.
> + *
> + * The function iterates through all tracked files. For each file, it performs
> + * the following sequence of cleanup actions:
> + *
> + * 1. If file is not yet retrieved, retrieves it, and calls can_finish() on
> + * every file in the session. If all can_finish return true, continue to
> + * finish.
> + * 2. Calls the handler's .finish() callback (via luo_file_finish_one) to
> + * allow for final resource cleanup within the handler.
> + * 3. Releases LUO's ownership reference on the 'struct file' via fput(). This
> + * is the counterpart to the get_file() call in luo_retrieve_file().
> + * 4. Removes the 'struct luo_file' from the session's internal list.
> + * 5. Frees the memory for the 'struct luo_file' instance itself.
> + *
> + * After successfully finishing all individual files, it frees the
> + * contiguous memory block that was used to transfer the serialized metadata
> + * from the previous kernel.
> + *
> + * Error Handling (Atomic Failure):
> + * This operation is atomic. If any handler's .can_finish() op fails, the entire
> + * function aborts immediately and returns an error.
> + *
> + * Context: Can be called from an ioctl handler in the new kernel.
> + * Return: 0 on success, or a negative errno on failure.
> + */
> +int luo_file_finish(struct luo_session *session)
> +{
> + struct list_head *files_list = &session->files_list;
> + struct luo_file *luo_file;
> + int err;
> +
> + if (!session->count)
> + return 0;
> +
> + lockdep_assert_held(&session->mutex);
> +
> + list_for_each_entry(luo_file, files_list, list) {
> + err = luo_file_can_finish_one(session, luo_file);
> + if (err)
> + return err;
> + }
> +
> + while (!list_empty(&session->files_list)) {
> + luo_file = list_last_entry(&session->files_list,
> + struct luo_file, list);
> +
> + luo_file_finish_one(session, luo_file);
> +
> + if (luo_file->file)
> + fput(luo_file->file);
> + list_del(&luo_file->list);
> + session->count--;
> + mutex_destroy(&luo_file->mutex);
> + kfree(luo_file);
> + }
> +
> + if (session->files) {
> + kho_restore_free(session->files);
> + session->files = NULL;
> + session->pgcnt = 0;
> + }
> +
> + return 0;
> +}
> +
> +/**
> + * luo_file_deserialize - Reconstructs the list of preserved files in the new kernel.
> + * @session: The incoming session containing the serialized file data from KHO.
> + *
> + * This function is called during the early boot process of the new kernel. It
> + * takes the raw, contiguous memory block of 'struct luo_file_ser' entries,
> + * provided by the previous kernel, and transforms it back into a live,
> + * in-memory linked list of 'struct luo_file' instances.
> + *
> + * For each serialized entry, it performs the following steps:
> + * 1. Reads the 'compatible' string.
> + * 2. Searches the global list of registered file handlers for one that
> + * matches the compatible string.
> + * 3. Allocates a new 'struct luo_file'.
> + * 4. Populates the new structure with the deserialized data (token, private
> + * data handle) and links it to the found handler. The 'file' pointer is
> + * initialized to NULL, as the file has not been retrieved yet.
> + * 5. Adds the new 'struct luo_file' to the session's files_list.
> + *
> + * This prepares the session for userspace, which can later call
> + * luo_retrieve_file() to restore the actual file descriptors.
> + *
> + * Context: Called from session deserialization.
> + */
> +int luo_file_deserialize(struct luo_session *session)
> +{
> + struct luo_file_ser *file_ser;
> + u64 i;
> +
> + lockdep_assert_held(&session->mutex);
> +
> + if (!session->files)
> + return 0;
> +
> + file_ser = session->files;
> + for (i = 0; i < session->count; i++) {
> + struct liveupdate_file_handler *fh;
> + bool handler_found = false;
> + struct luo_file *luo_file;
> +
> + list_for_each_entry(fh, &luo_file_handler_list, list) {
> + if (!strcmp(fh->compatible, file_ser[i].compatible)) {
> + handler_found = true;
> + break;
> + }
> + }
> +
> + if (!handler_found) {
> + pr_warn("No registered handler for compatible '%s'\n",
> + file_ser[i].compatible);
> + return -ENOENT;
> + }
> +
> + luo_file = kzalloc(sizeof(*luo_file), GFP_KERNEL);
> + if (!luo_file)
> + return -ENOMEM;
Shouldn't we free files allocated on the previous iterations?
> +
> + luo_file->fh = fh;
> + luo_file->file = NULL;
> + luo_file->serialized_data = file_ser[i].data;
> + luo_file->token = file_ser[i].token;
> + luo_file->retrieved = false;
> + mutex_init(&luo_file->mutex);
> + list_add_tail(&luo_file->list, &session->files_list);
> + }
> +
> + return 0;
> +}
> +
> +/**
> + * liveupdate_register_file_handler - Register a file handler with LUO.
> + * @fh: Pointer to a caller-allocated &struct liveupdate_file_handler.
> + * The caller must initialize this structure, including a unique
> + * 'compatible' string and a valid 'fh' callbacks. This function adds the
> + * handler to the global list of supported file handlers.
> + *
> + * Context: Typically called during module initialization for file types that
> + * support live update preservation.
> + *
> + * Return: 0 on success. Negative errno on failure.
> + */
> +int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
> +{
> + static DEFINE_MUTEX(register_file_handler_lock);
> + struct liveupdate_file_handler *fh_iter;
> +
> + if (!liveupdate_enabled())
> + return -EOPNOTSUPP;
> +
> + /*
> + * Once sessions have been deserialized, file handlers cannot be
> + * registered, it is too late.
> + */
> + if (WARN_ON(luo_session_is_deserialized()))
> + return -EBUSY;
> +
> + /* Sanity check that all required callbacks are set */
> + if (!fh->ops->preserve || !fh->ops->unpreserve ||
> + !fh->ops->retrieve || !fh->ops->finish) {
> + return -EINVAL;
> + }
> +
> + guard(mutex)(®ister_file_handler_lock);
> + list_for_each_entry(fh_iter, &luo_file_handler_list, list) {
> + if (!strcmp(fh_iter->compatible, fh->compatible)) {
> + pr_err("File handler registration failed: Compatible string '%s' already registered.\n",
> + fh->compatible);
> + return -EEXIST;
> + }
> + }
> +
> + if (!try_module_get(fh->ops->owner))
> + return -EAGAIN;
> +
> + INIT_LIST_HEAD(&fh->list);
> + list_add_tail(&fh->list, &luo_file_handler_list);
> +
> + return 0;
> +}
> +
> +/**
> + * liveupdate_get_token_outgoing - Get the token for a preserved file.
> + * @s: The outgoing liveupdate session.
> + * @file: The file object to search for.
> + * @tokenp: Output parameter for the found token.
> + *
> + * Searches the list of preserved files in an outgoing session for a matching
> + * file object. If found, the corresponding user-provided token is returned.
> + *
> + * This function is intended for in-kernel callers that need to correlate a
> + * file with its liveupdate token.
> + *
> + * Context: Can be called from any context that can acquire the session mutex.
> + * Return: 0 on success, -ENOENT if the file is not preserved in this session.
> + */
> +int liveupdate_get_token_outgoing(struct liveupdate_session *s,
> + struct file *file, u64 *tokenp)
> +{
This function is apparently unused.
> + struct luo_session *session = (struct luo_session *)s;
> + struct luo_file *luo_file;
> + int err = -ENOENT;
> +
> + list_for_each_entry(luo_file, &session->files_list, list) {
> + if (luo_file->file == file) {
> + if (tokenp)
> + *tokenp = luo_file->token;
> + err = 0;
> + break;
> + }
> + }
> +
> + return err;
> +}
> +
> +/**
> + * liveupdate_get_file_incoming - Retrieves a preserved file for in-kernel use.
> + * @s: The incoming liveupdate session (restored from the previous kernel).
> + * @token: The unique token identifying the file to retrieve.
> + * @filep: On success, this will be populated with a pointer to the retrieved
> + * 'struct file'.
> + *
> + * Provides a kernel-internal API for other subsystems to retrieve their
> + * preserved files after a live update. This function is a simple wrapper
> + * around luo_retrieve_file(), allowing callers to find a file by its token.
> + *
> + * The operation is idempotent; subsequent calls for the same token will return
> + * a pointer to the same 'struct file' object.
> + *
> + * The caller receives a pointer to the file with a reference incremented. The
> + * file's lifetime is managed by LUO and any userspace file
> + * descriptors. If the caller needs to hold a reference to the file beyond the
> + * immediate scope, it must call get_file() itself.
> + *
> + * Context: Can be called from any context in the new kernel that has a handle
> + * to a restored session.
> + * Return: 0 on success. Returns -ENOENT if no file with the matching token is
> + * found, or any other negative errno on failure.
> + */
> +int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
> + struct file **filep)
> +{
Ditto.
> + struct luo_session *session = (struct luo_session *)s;
> +
> + return luo_retrieve_file(session, token, filep);
> +}
> diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
> index 5185ad37a8c1..1a36f2383123 100644
> --- a/kernel/liveupdate/luo_internal.h
> +++ b/kernel/liveupdate/luo_internal.h
> @@ -70,4 +70,13 @@ int luo_session_serialize(void);
> int luo_session_deserialize(void);
> bool luo_session_is_deserialized(void);
>
> +int luo_preserve_file(struct luo_session *session, u64 token, int fd);
> +void luo_file_unpreserve_files(struct luo_session *session);
> +int luo_file_freeze(struct luo_session *session);
> +void luo_file_unfreeze(struct luo_session *session);
> +int luo_retrieve_file(struct luo_session *session, u64 token,
> + struct file **filep);
> +int luo_file_finish(struct luo_session *session);
> +int luo_file_deserialize(struct luo_session *session);
> +
> #endif /* _LINUX_LUO_INTERNAL_H */
> --
> 2.52.0.rc1.455.g30608eb744-goog
>
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 07/20] liveupdate: luo_session: Add ioctls for file preservation
From: Mike Rapoport @ 2025-11-16 18:25 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-8-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:53PM -0500, Pasha Tatashin wrote:
> Introducing the userspace interface and internal logic required to
> manage the lifecycle of file descriptors within a session. Previously, a
> session was merely a container; this change makes it a functional
> management unit.
>
> The following capabilities are added:
>
> A new set of ioctl commands are added, which operate on the file
> descriptor returned by CREATE_SESSION. This allows userspace to:
> - LIVEUPDATE_SESSION_PRESERVE_FD: Add a file descriptor to a session
> to be preserved across the live update.
> - LIVEUPDATE_SESSION_RETRIEVE_FD: Retrieve a preserved file in the
> new kernel using its unique token.
> - LIVEUPDATE_SESSION_FINISH: finish session
>
> The session's .release handler is enhanced to be state-aware. When a
> session's file descriptor is closed, it correctly unpreserves
> the session based on its current state before freeing all
> associated file resources.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/uapi/linux/liveupdate.h | 103 ++++++++++++++++++
> kernel/liveupdate/luo_session.c | 187 +++++++++++++++++++++++++++++++-
> 2 files changed, 286 insertions(+), 4 deletions(-)
...
> static int luo_session_release(struct inode *inodep, struct file *filep)
> {
> struct luo_session *session = filep->private_data;
> struct luo_session_header *sh;
> + int err = 0;
>
> /* If retrieved is set, it means this session is from incoming list */
> - if (session->retrieved)
> + if (session->retrieved) {
> sh = &luo_session_global.incoming;
> - else
> +
> + err = luo_session_finish_one(session);
> + if (err) {
> + pr_warn("Unable to finish session [%s] on release\n",
> + session->name);
return err;
and then else can go away here and luo_session_remove() and
luo_session_free() can be moved outside if (session->retrieved).
> + } else {
> + luo_session_remove(sh, session);
> + luo_session_free(session);
> + }
> +
> + } else {
> sh = &luo_session_global.outgoing;
>
> - luo_session_remove(sh, session);
> - luo_session_free(session);
> + scoped_guard(mutex, &session->mutex)
> + luo_file_unpreserve_files(session);
> + luo_session_remove(sh, session);
> + luo_session_free(session);
> + }
> +
> + return err;
> +}
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v5 22/22] tests/liveupdate: Add in-kernel liveupdate test
From: Mike Rapoport @ 2025-11-16 18:36 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, zhangguopeng,
linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <CA+CK2bBVRHwBu6a77gkvsbmWkQFDcTvNo+5aOT586mie13zqqA@mail.gmail.com>
On Wed, Nov 12, 2025 at 03:40:53PM -0500, Pasha Tatashin wrote:
> On Wed, Nov 12, 2025 at 3:24 PM Mike Rapoport <rppt@kernel.org> wrote:
> >
> > On Fri, Nov 07, 2025 at 04:03:20PM -0500, Pasha Tatashin wrote:
> > > Introduce an in-kernel test module to validate the core logic of the
> > > Live Update Orchestrator's File-Lifecycle-Bound feature. This
> > > provides a low-level, controlled environment to test FLB registration
> > > and callback invocation without requiring userspace interaction or
> > > actual kexec reboots.
> > >
> > > The test is enabled by the CONFIG_LIVEUPDATE_TEST Kconfig option.
> > >
> > > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > > ---
> > > kernel/liveupdate/luo_file.c | 2 +
> > > kernel/liveupdate/luo_internal.h | 8 ++
> > > lib/Kconfig.debug | 23 ++++++
> > > lib/tests/Makefile | 1 +
> > > lib/tests/liveupdate.c | 130 +++++++++++++++++++++++++++++++
> > > 5 files changed, 164 insertions(+)
> > > create mode 100644 lib/tests/liveupdate.c
> > >
> > > diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
> > > index 713069b96278..4c0a75918f3d 100644
> > > --- a/kernel/liveupdate/luo_file.c
> > > +++ b/kernel/liveupdate/luo_file.c
> > > @@ -829,6 +829,8 @@ int liveupdate_register_file_handler(struct liveupdate_file_handler *fh)
> > > INIT_LIST_HEAD(&fh->flb_list);
> > > list_add_tail(&fh->list, &luo_file_handler_list);
> > >
> > > + liveupdate_test_register(fh);
> > > +
> >
> > Do it mean that every flb user will be added here?
>
> No, FLB users will use:
>
> liveupdate_register_flb() from various subsystems. This
> liveupdate_test_register() is only to allow kernel test to register
> test-FLBs to every single file-handler for in-kernel testing purpose
> only.
Why the in kernel test cannot liveupdate_register_flb()?
> Pasha
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 18/20] selftests/liveupdate: Add kexec-based selftest for session lifecycle
From: Zhu Yanjun @ 2025-11-16 18:53 UTC (permalink / raw)
To: Pasha Tatashin, pratyush, jasonmiu, graf, rppt, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, linux, linux-kernel, linux-doc, linux-mm, gregkh, tglx,
mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, jgg, parav, leonro, witu,
hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-19-pasha.tatashin@soleen.com>
在 2025/11/15 15:34, Pasha Tatashin 写道:
> Introduce a kexec-based selftest, luo_kexec_simple, to validate the
> end-to-end lifecycle of a Live Update Orchestrator (LUO) session across
> a reboot.
>
> While existing tests verify the uAPI in a pre-reboot context, this test
> ensures that the core functionality—preserving state via Kexec Handover
> and restoring it in a new kernel—works as expected.
>
> The test operates in two stages, managing its state across the reboot by
> preserving a dedicated "state session" containing a memfd. This
> mechanism dogfoods the LUO feature itself for state tracking, making the
> test self-contained.
>
> The test validates the following sequence:
>
> Stage 1 (Pre-kexec):
> - Creates a test session (test-session).
> - Creates and preserves a memfd with a known data pattern into the test
> session.
> - Creates the state-tracking session to signal progression to Stage 2.
> - Executes a kexec reboot via a helper script.
>
> Stage 2 (Post-kexec):
> - Retrieves the state-tracking session to confirm it is in the
> post-reboot stage.
> - Retrieves the preserved test session.
> - Restores the memfd from the test session and verifies its contents
> match the original data pattern written in Stage 1.
> - Finalizes both the test and state sessions to ensure a clean
> teardown.
>
> The test relies on a helper script (do_kexec.sh) to perform the reboot
> and a shared utility library (luo_test_utils.c) for common LUO
> operations, keeping the main test logic clean and focused.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> tools/testing/selftests/liveupdate/.gitignore | 1 +
> tools/testing/selftests/liveupdate/Makefile | 32 ++++
> .../testing/selftests/liveupdate/do_kexec.sh | 16 ++
> .../selftests/liveupdate/luo_kexec_simple.c | 114 ++++++++++++
> .../selftests/liveupdate/luo_test_utils.c | 168 ++++++++++++++++++
> .../selftests/liveupdate/luo_test_utils.h | 39 ++++
> 6 files changed, 370 insertions(+)
> create mode 100755 tools/testing/selftests/liveupdate/do_kexec.sh
> create mode 100644 tools/testing/selftests/liveupdate/luo_kexec_simple.c
> create mode 100644 tools/testing/selftests/liveupdate/luo_test_utils.c
> create mode 100644 tools/testing/selftests/liveupdate/luo_test_utils.h
>
> diff --git a/tools/testing/selftests/liveupdate/.gitignore b/tools/testing/selftests/liveupdate/.gitignore
> index af6e773cf98f..daeef116174d 100644
> --- a/tools/testing/selftests/liveupdate/.gitignore
> +++ b/tools/testing/selftests/liveupdate/.gitignore
> @@ -1 +1,2 @@
> /liveupdate
> +/luo_kexec_simple
> diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
> index 2a573c36016e..1563ac84006a 100644
> --- a/tools/testing/selftests/liveupdate/Makefile
> +++ b/tools/testing/selftests/liveupdate/Makefile
> @@ -1,7 +1,39 @@
> # SPDX-License-Identifier: GPL-2.0-only
> +
> +KHDR_INCLUDES ?= -I../../../../usr/include
> CFLAGS += -Wall -O2 -Wno-unused-function
> CFLAGS += $(KHDR_INCLUDES)
> +LDFLAGS += -static
> +OUTPUT ?= .
> +
> +# --- Test Configuration (Edit this section when adding new tests) ---
> +LUO_SHARED_SRCS := luo_test_utils.c
> +LUO_SHARED_HDRS += luo_test_utils.h
> +
> +LUO_MANUAL_TESTS += luo_kexec_simple
> +
> +TEST_FILES += do_kexec.sh
>
> TEST_GEN_PROGS += liveupdate
>
> +# --- Automatic Rule Generation (Do not edit below) ---
> +
> +TEST_GEN_PROGS_EXTENDED += $(LUO_MANUAL_TESTS)
> +
> +# Define the full list of sources for each manual test.
> +$(foreach test,$(LUO_MANUAL_TESTS), \
> + $(eval $(test)_SOURCES := $(test).c $(LUO_SHARED_SRCS)))
> +
> +# This loop automatically generates an explicit build rule for each manual test.
> +# It includes dependencies on the shared headers and makes the output
> +# executable.
> +# Note the use of '$$' to escape automatic variables for the 'eval' command.
> +$(foreach test,$(LUO_MANUAL_TESTS), \
> + $(eval $(OUTPUT)/$(test): $($(test)_SOURCES) $(LUO_SHARED_HDRS) \
> + $(call msg,LINK,,$$@) ; \
> + $(Q)$(LINK.c) $$^ $(LDLIBS) -o $$@ ; \
> + $(Q)chmod +x $$@ \
> + ) \
> +)
> +
> include ../lib.mk
> diff --git a/tools/testing/selftests/liveupdate/do_kexec.sh b/tools/testing/selftests/liveupdate/do_kexec.sh
> new file mode 100755
> index 000000000000..3c7c6cafbef8
> --- /dev/null
> +++ b/tools/testing/selftests/liveupdate/do_kexec.sh
> @@ -0,0 +1,16 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +set -e
> +
> +# Use $KERNEL and $INITRAMFS to pass custom Kernel and optional initramfs
> +
> +KERNEL="${KERNEL:-/boot/bzImage}"
> +set -- -l -s --reuse-cmdline "$KERNEL"
> +
> +INITRAMFS="${INITRAMFS:-/boot/initramfs}"
> +if [ -f "$INITRAMFS" ]; then
> + set -- "$@" --initrd="$INITRAMFS"
> +fi
> +
> +kexec "$@"
> +kexec -e
Thanks a lot. Just with kernel image, it is not enough to boot the host.
Adding initramfs will avoid the crash when the host boots.
I have made tests to verify this.
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Zhu Yanjun
> diff --git a/tools/testing/selftests/liveupdate/luo_kexec_simple.c b/tools/testing/selftests/liveupdate/luo_kexec_simple.c
> new file mode 100644
> index 000000000000..67ab6ebf9eec
> --- /dev/null
> +++ b/tools/testing/selftests/liveupdate/luo_kexec_simple.c
> @@ -0,0 +1,114 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +/*
> + * Copyright (c) 2025, Google LLC.
> + * Pasha Tatashin <pasha.tatashin@soleen.com>
> + *
> + * A simple selftest to validate the end-to-end lifecycle of a LUO session
> + * across a single kexec reboot.
> + */
> +
> +#include "luo_test_utils.h"
> +
> +/* Test-specific constants are now defined locally */
> +#define KEXEC_SCRIPT "./do_kexec.sh"
> +#define TEST_SESSION_NAME "test-session"
> +#define TEST_MEMFD_TOKEN 0x1A
> +#define TEST_MEMFD_DATA "hello kexec world"
> +
> +/* Constants for the state-tracking mechanism, specific to this test file. */
> +#define STATE_SESSION_NAME "kexec_simple_state"
> +#define STATE_MEMFD_TOKEN 999
> +
> +/* Stage 1: Executed before the kexec reboot. */
> +static void run_stage_1(int luo_fd)
> +{
> + int session_fd;
> +
> + ksft_print_msg("[STAGE 1] Starting pre-kexec setup...\n");
> +
> + ksft_print_msg("[STAGE 1] Creating state file for next stage (2)...\n");
> + create_state_file(luo_fd, STATE_SESSION_NAME, STATE_MEMFD_TOKEN, 2);
> +
> + ksft_print_msg("[STAGE 1] Creating session '%s' and preserving memfd...\n",
> + TEST_SESSION_NAME);
> + session_fd = luo_create_session(luo_fd, TEST_SESSION_NAME);
> + if (session_fd < 0)
> + fail_exit("luo_create_session for '%s'", TEST_SESSION_NAME);
> +
> + if (create_and_preserve_memfd(session_fd, TEST_MEMFD_TOKEN,
> + TEST_MEMFD_DATA) < 0) {
> + fail_exit("create_and_preserve_memfd for token %#x",
> + TEST_MEMFD_TOKEN);
> + }
> +
> + ksft_print_msg("[STAGE 1] Executing kexec...\n");
> + if (system(KEXEC_SCRIPT) != 0)
> + fail_exit("kexec script failed");
> + exit(EXIT_FAILURE);
> +}
> +
> +/* Stage 2: Executed after the kexec reboot. */
> +static void run_stage_2(int luo_fd, int state_session_fd)
> +{
> + int session_fd, mfd, stage;
> +
> + ksft_print_msg("[STAGE 2] Starting post-kexec verification...\n");
> +
> + restore_and_read_stage(state_session_fd, STATE_MEMFD_TOKEN, &stage);
> + if (stage != 2)
> + fail_exit("Expected stage 2, but state file contains %d", stage);
> +
> + ksft_print_msg("[STAGE 2] Retrieving session '%s'...\n", TEST_SESSION_NAME);
> + session_fd = luo_retrieve_session(luo_fd, TEST_SESSION_NAME);
> + if (session_fd < 0)
> + fail_exit("luo_retrieve_session for '%s'", TEST_SESSION_NAME);
> +
> + ksft_print_msg("[STAGE 2] Restoring and verifying memfd (token %#x)...\n",
> + TEST_MEMFD_TOKEN);
> + mfd = restore_and_verify_memfd(session_fd, TEST_MEMFD_TOKEN,
> + TEST_MEMFD_DATA);
> + if (mfd < 0)
> + fail_exit("restore_and_verify_memfd for token %#x", TEST_MEMFD_TOKEN);
> + close(mfd);
> +
> + ksft_print_msg("[STAGE 2] Test data verified successfully.\n");
> + ksft_print_msg("[STAGE 2] Finalizing test session...\n");
> + if (luo_session_finish(session_fd) < 0)
> + fail_exit("luo_session_finish for test session");
> + close(session_fd);
> +
> + ksft_print_msg("[STAGE 2] Finalizing state session...\n");
> + if (luo_session_finish(state_session_fd) < 0)
> + fail_exit("luo_session_finish for state session");
> + close(state_session_fd);
> +
> + ksft_print_msg("\n--- SIMPLE KEXEC TEST PASSED ---\n");
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + int luo_fd;
> + int state_session_fd;
> +
> + luo_fd = luo_open_device();
> + if (luo_fd < 0)
> + ksft_exit_skip("Failed to open %s. Is the luo module loaded?\n",
> + LUO_DEVICE);
> +
> + /*
> + * Determine the stage by attempting to retrieve the state session.
> + * If it doesn't exist (ENOENT), we are in Stage 1 (pre-kexec).
> + */
> + state_session_fd = luo_retrieve_session(luo_fd, STATE_SESSION_NAME);
> + if (state_session_fd == -ENOENT) {
> + run_stage_1(luo_fd);
> + } else if (state_session_fd >= 0) {
> + /* We got a valid handle, pass it directly to stage 2 */
> + run_stage_2(luo_fd, state_session_fd);
> + } else {
> + fail_exit("Failed to check for state session");
> + }
> +
> + close(luo_fd);
> +}
> diff --git a/tools/testing/selftests/liveupdate/luo_test_utils.c b/tools/testing/selftests/liveupdate/luo_test_utils.c
> new file mode 100644
> index 000000000000..0a24105cbc54
> --- /dev/null
> +++ b/tools/testing/selftests/liveupdate/luo_test_utils.c
> @@ -0,0 +1,168 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +/*
> + * Copyright (c) 2025, Google LLC.
> + * Pasha Tatashin <pasha.tatashin@soleen.com>
> + */
> +
> +#define _GNU_SOURCE
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <sys/ioctl.h>
> +#include <sys/syscall.h>
> +#include <sys/mman.h>
> +#include <errno.h>
> +#include <stdarg.h>
> +
> +#include "luo_test_utils.h"
> +
> +int luo_open_device(void)
> +{
> + return open(LUO_DEVICE, O_RDWR);
> +}
> +
> +int luo_create_session(int luo_fd, const char *name)
> +{
> + struct liveupdate_ioctl_create_session arg = { .size = sizeof(arg) };
> +
> + snprintf((char *)arg.name, LIVEUPDATE_SESSION_NAME_LENGTH, "%.*s",
> + LIVEUPDATE_SESSION_NAME_LENGTH - 1, name);
> +
> + if (ioctl(luo_fd, LIVEUPDATE_IOCTL_CREATE_SESSION, &arg) < 0)
> + return -errno;
> +
> + return arg.fd;
> +}
> +
> +int luo_retrieve_session(int luo_fd, const char *name)
> +{
> + struct liveupdate_ioctl_retrieve_session arg = { .size = sizeof(arg) };
> +
> + snprintf((char *)arg.name, LIVEUPDATE_SESSION_NAME_LENGTH, "%.*s",
> + LIVEUPDATE_SESSION_NAME_LENGTH - 1, name);
> +
> + if (ioctl(luo_fd, LIVEUPDATE_IOCTL_RETRIEVE_SESSION, &arg) < 0)
> + return -errno;
> +
> + return arg.fd;
> +}
> +
> +int create_and_preserve_memfd(int session_fd, int token, const char *data)
> +{
> + struct liveupdate_session_preserve_fd arg = { .size = sizeof(arg) };
> + long page_size = sysconf(_SC_PAGE_SIZE);
> + void *map = MAP_FAILED;
> + int mfd = -1, ret = -1;
> +
> + mfd = memfd_create("test_mfd", 0);
> + if (mfd < 0)
> + return -errno;
> +
> + if (ftruncate(mfd, page_size) != 0)
> + goto out;
> +
> + map = mmap(NULL, page_size, PROT_WRITE, MAP_SHARED, mfd, 0);
> + if (map == MAP_FAILED)
> + goto out;
> +
> + snprintf(map, page_size, "%s", data);
> + munmap(map, page_size);
> +
> + arg.fd = mfd;
> + arg.token = token;
> + if (ioctl(session_fd, LIVEUPDATE_SESSION_PRESERVE_FD, &arg) < 0)
> + goto out;
> +
> + ret = 0;
> +out:
> + if (ret != 0 && errno != 0)
> + ret = -errno;
> + if (mfd >= 0)
> + close(mfd);
> + return ret;
> +}
> +
> +int restore_and_verify_memfd(int session_fd, int token,
> + const char *expected_data)
> +{
> + struct liveupdate_session_retrieve_fd arg = { .size = sizeof(arg) };
> + long page_size = sysconf(_SC_PAGE_SIZE);
> + void *map = MAP_FAILED;
> + int mfd = -1, ret = -1;
> +
> + arg.token = token;
> + if (ioctl(session_fd, LIVEUPDATE_SESSION_RETRIEVE_FD, &arg) < 0)
> + return -errno;
> + mfd = arg.fd;
> +
> + map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, mfd, 0);
> + if (map == MAP_FAILED)
> + goto out;
> +
> + if (expected_data && strcmp(expected_data, map) != 0) {
> + ksft_print_msg("Data mismatch! Expected '%s', Got '%s'\n",
> + expected_data, (char *)map);
> + ret = -EINVAL;
> + goto out_munmap;
> + }
> +
> + ret = mfd;
> +out_munmap:
> + munmap(map, page_size);
> +out:
> + if (ret < 0 && errno != 0)
> + ret = -errno;
> + if (ret < 0 && mfd >= 0)
> + close(mfd);
> + return ret;
> +}
> +
> +int luo_session_finish(int session_fd)
> +{
> + struct liveupdate_session_finish arg = { .size = sizeof(arg) };
> +
> + if (ioctl(session_fd, LIVEUPDATE_SESSION_FINISH, &arg) < 0)
> + return -errno;
> +
> + return 0;
> +}
> +
> +void create_state_file(int luo_fd, const char *session_name, int token,
> + int next_stage)
> +{
> + char buf[32];
> + int state_session_fd;
> +
> + state_session_fd = luo_create_session(luo_fd, session_name);
> + if (state_session_fd < 0)
> + fail_exit("luo_create_session for state tracking");
> +
> + snprintf(buf, sizeof(buf), "%d", next_stage);
> + if (create_and_preserve_memfd(state_session_fd, token, buf) < 0)
> + fail_exit("create_and_preserve_memfd for state tracking");
> +
> + /*
> + * DO NOT close session FD, otherwise it is going to be unpreserved
> + */
> +}
> +
> +void restore_and_read_stage(int state_session_fd, int token, int *stage)
> +{
> + char buf[32] = {0};
> + int mfd;
> +
> + mfd = restore_and_verify_memfd(state_session_fd, token, NULL);
> + if (mfd < 0)
> + fail_exit("failed to restore state memfd");
> +
> + if (read(mfd, buf, sizeof(buf) - 1) < 0)
> + fail_exit("failed to read state mfd");
> +
> + *stage = atoi(buf);
> +
> + close(mfd);
> +}
> diff --git a/tools/testing/selftests/liveupdate/luo_test_utils.h b/tools/testing/selftests/liveupdate/luo_test_utils.h
> new file mode 100644
> index 000000000000..093e787b9f4b
> --- /dev/null
> +++ b/tools/testing/selftests/liveupdate/luo_test_utils.h
> @@ -0,0 +1,39 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Copyright (c) 2025, Google LLC.
> + * Pasha Tatashin <pasha.tatashin@soleen.com>
> + *
> + * Utility functions for LUO kselftests.
> + */
> +
> +#ifndef LUO_TEST_UTILS_H
> +#define LUO_TEST_UTILS_H
> +
> +#include <errno.h>
> +#include <string.h>
> +#include <linux/liveupdate.h>
> +#include "../kselftest.h"
> +
> +#define LUO_DEVICE "/dev/liveupdate"
> +
> +#define fail_exit(fmt, ...) \
> + ksft_exit_fail_msg("[%s:%d] " fmt " (errno: %s)\n", \
> + __func__, __LINE__, ##__VA_ARGS__, strerror(errno))
> +
> +/* Generic LUO and session management helpers */
> +int luo_open_device(void);
> +int luo_create_session(int luo_fd, const char *name);
> +int luo_retrieve_session(int luo_fd, const char *name);
> +int luo_session_finish(int session_fd);
> +
> +/* Generic file preservation and restoration helpers */
> +int create_and_preserve_memfd(int session_fd, int token, const char *data);
> +int restore_and_verify_memfd(int session_fd, int token, const char *expected_data);
> +
> +/* Kexec state-tracking helpers */
> +void create_state_file(int luo_fd, const char *session_name, int token,
> + int next_stage);
> +void restore_and_read_stage(int state_session_fd, int token, int *stage);
> +
> +#endif /* LUO_TEST_UTILS_H */
^ permalink raw reply
* Re: [PATCH v6 02/20] liveupdate: luo_core: integrate with KHO
From: Mike Rapoport @ 2025-11-16 19:16 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <CA+CK2bDu2FdzyotSwBpGwQtiisv=3f6gC7DzOpebPCxmmpwMYw@mail.gmail.com>
On Sun, Nov 16, 2025 at 09:55:30AM -0500, Pasha Tatashin wrote:
> On Sun, Nov 16, 2025 at 7:43 AM Mike Rapoport <rppt@kernel.org> wrote:
> >
> > > +static int __init liveupdate_early_init(void)
> > > +{
> > > + int err;
> > > +
> > > + err = luo_early_startup();
> > > + if (err) {
> > > + pr_err("The incoming tree failed to initialize properly [%pe], disabling live update\n",
> > > + ERR_PTR(err));
> >
> > How do we report this to the userspace?
> > I think the decision what to do in this case belongs there. Even if it's
> > down to choosing between plain kexec and full reboot, it's still a policy
> > that should be implemented in userspace.
>
> I agree that policy belongs in userspace, and that is how we designed
> it. In this specific failure case (ABI mismatch or corrupt FDT), the
> preserved state is unrecoverable by the kernel. We cannot parse the
> incoming data, so we cannot offer it to userspace.
>
> We report this state by not registering the /dev/liveupdate device.
> When the userspace agent attempts to initialize, it receives ENOENT.
> At that point, the agent exercises its policy:
>
> - Check dmesg for the specific error and report the failure to the
> fleet control plane.
Hmm, this is not nice. I think we still should register /dev/liveupdate and
let userspace discover this error via /dev/liveupdate ABIs.
> - Trigger a fresh (kexec or cold) reboot to reset unreclaimable resources.
>
> Pasha
>
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 01/20] liveupdate: luo_core: luo_ioctl: Live Update Orchestrator
From: Andrew Morton @ 2025-11-17 2:54 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, rppt, dmatlack, rientjes, corbet,
rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-2-pasha.tatashin@soleen.com>
On Sat, 15 Nov 2025 18:33:47 -0500 Pasha Tatashin <pasha.tatashin@soleen.com> wrote:
> Introduce LUO, a mechanism intended to facilitate kernel updates while
> keeping designated devices operational across the transition (e.g., via
> kexec).
Thanks, I updated mm.git's mm-unstable branch to this version. I
expect at least one more version as a result of feedback for this v6.
I wasn't able to reproduce Stephen's build error
(https://lkml.kernel.org/r/20251117093614.1490d048@canb.auug.org.au)
with this series.
^ permalink raw reply
* Re: [PATCH v6 08/20] liveupdate: luo_flb: Introduce File-Lifecycle-Bound global state
From: Mike Rapoport @ 2025-11-17 9:39 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-9-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:54PM -0500, Pasha Tatashin wrote:
> Introduce a mechanism for managing global kernel state whose lifecycle
> is tied to the preservation of one or more files. This is necessary for
> subsystems where multiple preserved file descriptors depend on a single,
> shared underlying resource.
>
> An example is HugeTLB, where multiple file descriptors such as memfd and
> guest_memfd may rely on the state of a single HugeTLB subsystem.
> Preserving this state for each individual file would be redundant and
> incorrect. The state should be preserved only once when the first file
> is preserved, and restored/finished only once the last file is handled.
>
> This patch introduces File-Lifecycle-Bound (FLB) objects to solve this
> problem. An FLB is a global, reference-counted object with a defined set
> of operations:
>
> - A file handler (struct liveupdate_file_handler) declares a dependency
> on one or more FLBs via a new registration function,
> liveupdate_register_flb().
> - When the first file depending on an FLB is preserved, the FLB's
> .preserve() callback is invoked to save the shared global state. The
> reference count is then incremented for each subsequent file.
> - Conversely, when the last file is unpreserved (before reboot) or
> finished (after reboot), the FLB's .unpreserve() or .finish() callback
> is invoked to clean up the global resource.
>
> The implementation includes:
>
> - A new set of ABI definitions (luo_flb_ser, luo_flb_head_ser) and a
> corresponding FDT node (luo-flb) to serialize the state of all active
> FLBs and pass them via Kexec Handover.
> - Core logic in luo_flb.c to manage FLB registration, reference
> counting, and the invocation of lifecycle callbacks.
> - An API (liveupdate_flb_*_locked/*_unlock) for other kernel subsystems
> to safely access the live object managed by an FLB, both before and
> after the live update.
>
> This framework provides the necessary infrastructure for more complex
> subsystems like IOMMU, VFIO, and KVM to integrate with the Live Update
> Orchestrator.
The concept makes sense to me, but it's hard to review the implementation
without an actual user.
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/linux/liveupdate.h | 116 +++++
> include/linux/liveupdate/abi/luo.h | 76 ++++
> kernel/liveupdate/Makefile | 1 +
> kernel/liveupdate/luo_core.c | 7 +-
> kernel/liveupdate/luo_file.c | 8 +
> kernel/liveupdate/luo_flb.c | 658 +++++++++++++++++++++++++++++
> kernel/liveupdate/luo_internal.h | 7 +
> 7 files changed, 872 insertions(+), 1 deletion(-)
> create mode 100644 kernel/liveupdate/luo_flb.c
>
> diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
> index 4a5d4dd9905a..36a831ae3ead 100644
> --- a/include/linux/liveupdate.h
> +++ b/include/linux/liveupdate.h
> @@ -14,6 +14,7 @@
> #include <uapi/linux/liveupdate.h>
>
> struct liveupdate_file_handler;
> +struct liveupdate_flb;
> struct liveupdate_session;
> struct file;
>
> @@ -81,6 +82,7 @@ struct liveupdate_file_ops {
> * associated with individual &struct file instances.
> * @list: Used for linking this handler instance into a global
> * list of registered file handlers.
> + * @flb_list: A list of FLB dependencies.
> *
> * Modules that want to support live update for specific file types should
> * register an instance of this structure. LUO uses this registration to
> @@ -91,6 +93,80 @@ struct liveupdate_file_handler {
> const struct liveupdate_file_ops *ops;
> const char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
> struct list_head list;
> + struct list_head flb_list;
> +};
> +
> +/**
> + * struct liveupdate_flb_op_args - Arguments for FLB operation callbacks.
> + * @flb: The global FLB instance for which this call is performed.
> + * @data: For .preserve(): [OUT] The callback sets this field.
> + * For .unpreserve(): [IN] The handle from .preserve().
> + * For .retrieve(): [IN] The handle from .preserve().
> + * @obj: For .preserve(): [OUT] Sets this to the live object.
> + * For .retrieve(): [OUT] Sets this to the live object.
> + * For .finish(): [IN] The live object from .retrieve().
> + *
> + * This structure bundles all parameters for the FLB operation callbacks.
> + */
> +struct liveupdate_flb_op_args {
> + struct liveupdate_flb *flb;
> + u64 data;
> + void *obj;
> +};
> +
> +/**
> + * struct liveupdate_flb_ops - Callbacks for global File-Lifecycle-Bound data.
> + * @preserve: Called when the first file using this FLB is preserved.
> + * The callback must save its state and return a single,
> + * self-contained u64 handle by setting the 'argp->data'
> + * field and 'argp->obj'.
> + * @unpreserve: Called when the last file using this FLB is unpreserved
> + * (aborted before reboot). Receives the handle via
> + * 'argp->data' and live object via 'argp->obj'.
> + * @retrieve: Called on-demand in the new kernel, the first time a
> + * component requests access to the shared object. It receives
> + * the preserved handle via 'argp->data' and must reconstruct
> + * the live object, returning it by setting the 'argp->obj'
> + * field.
> + * @finish: Called in the new kernel when the last file using this FLB
> + * is finished. Receives the live object via 'argp->obj' for
> + * cleanup.
> + * @owner: Module reference
> + *
> + * Operations that manage global shared data with file bound lifecycle,
> + * triggered by the first file that uses it and concluded by the last file that
> + * uses it, across all sessions.
> + */
> +struct liveupdate_flb_ops {
> + int (*preserve)(struct liveupdate_flb_op_args *argp);
> + void (*unpreserve)(struct liveupdate_flb_op_args *argp);
> + int (*retrieve)(struct liveupdate_flb_op_args *argp);
> + void (*finish)(struct liveupdate_flb_op_args *argp);
> + struct module *owner;
> +};
> +
> +/**
> + * struct liveupdate_flb - A global definition for a shared data object.
> + * @ops: Callback functions
> + * @compatible: The compatibility string (e.g., "iommu-core-v1"
> + * that uniquely identifies the FLB type this handler
> + * supports. This is matched against the compatible string
> + * associated with individual &struct liveupdate_flb
> + * instances.
> + * @list: A global list of registered FLBs.
> + * @internal: Internal state, set in liveupdate_init_flb().
> + *
> + * This struct is the "template" that a driver registers to define a shared,
> + * file-lifecycle-bound object. The actual runtime state (the live object,
> + * refcount, etc.) is managed internally by the LUO core.
> + * Use liveupdate_init_flb() to initialize this struct before using it in
> + * other functions.
> + */
> +struct liveupdate_flb {
> + const struct liveupdate_flb_ops *ops;
> + const char compatible[LIVEUPDATE_FLB_COMPAT_LENGTH];
> + struct list_head list;
> + void *internal;
Can't list be a part of internal?
And don't we usually call this .private rather than .internal?
> };
>
> #ifdef CONFIG_LIVEUPDATE
> @@ -111,6 +187,17 @@ int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
> int liveupdate_get_token_outgoing(struct liveupdate_session *s,
> struct file *file, u64 *tokenp);
>
> +/* Before using FLB for the first time it should be initialized */
> +int liveupdate_init_flb(struct liveupdate_flb *flb);
> +
> +int liveupdate_register_flb(struct liveupdate_file_handler *h,
> + struct liveupdate_flb *flb);
While these are obvious ...
> +
> +int liveupdate_flb_incoming_locked(struct liveupdate_flb *flb, void **objp);
> +void liveupdate_flb_incoming_unlock(struct liveupdate_flb *flb, void *obj);
> +int liveupdate_flb_outgoing_locked(struct liveupdate_flb *flb, void **objp);
> +void liveupdate_flb_outgoing_unlock(struct liveupdate_flb *flb, void *obj);
> +
... it's not very clear what these APIs are for and how they are going to be
used.
> #else /* CONFIG_LIVEUPDATE */
...
> +int liveupdate_register_flb(struct liveupdate_file_handler *h,
> + struct liveupdate_flb *flb)
> +{
> + struct luo_flb_internal *internal = flb->internal;
> + struct luo_flb_link *link __free(kfree) = NULL;
> + static DEFINE_MUTEX(register_flb_lock);
> + struct liveupdate_flb *gflb;
> + struct luo_flb_link *iter;
> +
> + if (!liveupdate_enabled())
> + return -EOPNOTSUPP;
> +
> + if (WARN_ON(!h || !flb || !internal))
> + return -EINVAL;
> +
> + if (WARN_ON(!flb->ops->preserve || !flb->ops->unpreserve ||
> + !flb->ops->retrieve || !flb->ops->finish)) {
> + return -EINVAL;
> + }
> +
> + /*
> + * Once session/files have been deserialized, FLBs cannot be registered,
> + * it is too late. Deserialization uses file handlers, and FLB registers
> + * to file handlers.
> + */
> + if (WARN_ON(luo_session_is_deserialized()))
> + return -EBUSY;
> +
> + /*
> + * File handler must already be registered, as it is initializes the
> + * flb_list
> + */
> + if (WARN_ON(list_empty(&h->list)))
> + return -EINVAL;
> +
> + link = kzalloc(sizeof(*link), GFP_KERNEL);
> + if (!link)
> + return -ENOMEM;
> +
> + guard(mutex)(®ister_flb_lock);
> +
> + /* Check that this FLB is not already linked to this file handler */
> + list_for_each_entry(iter, &h->flb_list, list) {
> + if (iter->flb == flb)
> + return -EEXIST;
> + }
> +
> + /* Is this FLB linked to global list ? */
Maybe:
/*
* If this FLB is not linked to global list it's first time the FLB
* is registered
*/
> + if (list_empty(&flb->list)) {
> + if (luo_flb_global.count == LUO_FLB_MAX)
> + return -ENOSPC;
> +
> + /* Check that compatible string is unique in global list */
> + list_for_each_entry(gflb, &luo_flb_global.list, list) {
> + if (!strcmp(gflb->compatible, flb->compatible))
> + return -EEXIST;
> + }
> +
> + if (!try_module_get(flb->ops->owner))
> + return -EAGAIN;
> +
> + list_add_tail(&flb->list, &luo_flb_global.list);
> + luo_flb_global.count++;
> + }
> +
> + /* Finally, link the FLB to the file handler */
> + link->flb = flb;
> + list_add_tail(&no_free_ptr(link)->list, &h->flb_list);
> +
> + return 0;
> +}
> +
> +/**
> + * liveupdate_flb_incoming_locked - Lock and retrieve the incoming FLB object.
> + * @flb: The FLB definition.
> + * @objp: Output parameter; will be populated with the live shared object.
> + *
> + * Acquires the FLB's internal lock and returns a pointer to its shared live
> + * object for the incoming (post-reboot) path.
> + *
> + * If this is the first time the object is requested in the new kernel, this
> + * function will trigger the FLB's .retrieve() callback to reconstruct the
> + * object from its preserved state. Subsequent calls will return the same
> + * cached object.
> + *
> + * The caller MUST call liveupdate_flb_incoming_unlock() to release the lock.
> + *
> + * Return: 0 on success, or a negative errno on failure. -ENODATA means no
> + * incoming FLB data, -ENOENT means specific flb not found in the incoming
> + * data, and -EOPNOTSUPP when live update is disabled or not configured.
> + */
> +int liveupdate_flb_incoming_locked(struct liveupdate_flb *flb, void **objp)
> +{
> + struct luo_flb_internal *internal = flb->internal;
> +
> + if (!liveupdate_enabled())
> + return -EOPNOTSUPP;
> +
> + if (WARN_ON(!internal))
> + return -EINVAL;
> +
> + if (!internal->incoming.obj) {
> + int err = luo_flb_retrieve_one(flb);
> +
> + if (err)
> + return err;
> + }
> +
> + mutex_lock(&internal->incoming.lock);
> + *objp = internal->incoming.obj;
> +
> + return 0;
> +}
> +
> +/**
> + * liveupdate_flb_incoming_unlock - Unlock an incoming FLB object.
> + * @flb: The FLB definition.
> + * @obj: The object that was returned by the _locked call (used for validation).
> + *
> + * Releases the internal lock acquired by liveupdate_flb_incoming_locked().
> + */
> +void liveupdate_flb_incoming_unlock(struct liveupdate_flb *flb, void *obj)
> +{
> + struct luo_flb_internal *internal = flb->internal;
> +
> + lockdep_assert_held(&internal->incoming.lock);
> + internal->incoming.obj = obj;
The comment says obj is for validation and here it's assigned to flb.
Something is off here :)
> + mutex_unlock(&internal->incoming.lock);
> +}
> +
> +/**
> + * liveupdate_flb_outgoing_locked - Lock and retrieve the outgoing FLB object.
> + * @flb: The FLB definition.
> + * @objp: Output parameter; will be populated with the live shared object.
> + *
> + * Acquires the FLB's internal lock and returns a pointer to its shared live
> + * object for the outgoing (pre-reboot) path.
> + *
> + * This function assumes the object has already been created by the FLB's
> + * .preserve() callback, which is triggered when the first dependent file
> + * is preserved.
> + *
> + * The caller MUST call liveupdate_flb_outgoing_unlock() to release the lock.
> + *
> + * Return: 0 on success, or a negative errno on failure.
> + */
> +int liveupdate_flb_outgoing_locked(struct liveupdate_flb *flb, void **objp)
> +{
> + struct luo_flb_internal *internal = flb->internal;
> +
> + if (!liveupdate_enabled())
> + return -EOPNOTSUPP;
> +
> + if (WARN_ON(!internal))
> + return -EINVAL;
> +
> + mutex_lock(&internal->outgoing.lock);
> +
> + /* The object must exist if any file is being preserved */
> + if (WARN_ON_ONCE(!internal->outgoing.obj)) {
> + mutex_unlock(&internal->outgoing.lock);
> + return -ENOENT;
> + }
_incoming_locked() and outgoing_locked() are nearly identical, it seems we
can have the common part in a
static liveupdate_flb_locked(struct luo_flb_state *state).
liveupdate_flb_incoming_locked() will be oneline wrapper and
liveupdate_flb_outgoing_locked() will have this WARN_ON if obj is NULL.
> +
> + *objp = internal->outgoing.obj;
> +
> + return 0;
> +}
> +
> +/**
> + * liveupdate_flb_outgoing_unlock - Unlock an outgoing FLB object.
> + * @flb: The FLB definition.
> + * @obj: The object that was returned by the _locked call (used for validation).
> + *
> + * Releases the internal lock acquired by liveupdate_flb_outgoing_locked().
> + */
> +void liveupdate_flb_outgoing_unlock(struct liveupdate_flb *flb, void *obj)
> +{
> + struct luo_flb_internal *internal = flb->internal;
> +
> + lockdep_assert_held(&internal->outgoing.lock);
> + internal->outgoing.obj = obj;
So it is assignment or validation? ;-)
This one is a copy of liveupdate_flb_incoming_unlock(),
> + mutex_unlock(&internal->outgoing.lock);
> +}
> +
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 10/20] MAINTAINERS: add liveupdate entry
From: Mike Rapoport @ 2025-11-17 9:40 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-11-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:56PM -0500, Pasha Tatashin wrote:
> Add a MAINTAINERS file entry for the new Live Update Orchestrator
> introduced in previous patches.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> MAINTAINERS | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 500789529359..bc9f5c6f0e80 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -14464,6 +14464,17 @@ F: kernel/module/livepatch.c
> F: samples/livepatch/
> F: tools/testing/selftests/livepatch/
>
> +LIVE UPDATE
> +M: Pasha Tatashin <pasha.tatashin@soleen.com>
Please count me in :)
> +L: linux-kernel@vger.kernel.org
> +S: Maintained
> +F: Documentation/core-api/liveupdate.rst
> +F: Documentation/userspace-api/liveupdate.rst
> +F: include/linux/liveupdate.h
> +F: include/linux/liveupdate/
> +F: include/uapi/linux/liveupdate.h
> +F: kernel/liveupdate/
> +
> LLC (802.2)
> L: netdev@vger.kernel.org
> S: Odd fixes
> --
> 2.52.0.rc1.455.g30608eb744-goog
>
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 11/20] mm: shmem: use SHMEM_F_* flags instead of VM_* flags
From: Mike Rapoport @ 2025-11-17 9:48 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-12-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:57PM -0500, Pasha Tatashin wrote:
> From: Pratyush Yadav <ptyadav@amazon.de>
>
> shmem_inode_info::flags can have the VM flags VM_NORESERVE and
> VM_LOCKED. These are used to suppress pre-accounting or to lock the
> pages in the inode respectively. Using the VM flags directly makes it
> difficult to add shmem-specific flags that are unrelated to VM behavior
> since one would need to find a VM flag not used by shmem and re-purpose
> it.
>
> Introduce SHMEM_F_NORESERVE and SHMEM_F_LOCKED which represent the same
> information, but their bits are independent of the VM flags. Callers can
> still pass VM_NORESERVE to shmem_get_inode(), but it gets transformed to
> the shmem-specific flag internally.
>
> No functional changes intended.
>
> Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> include/linux/shmem_fs.h | 6 ++++++
> mm/shmem.c | 28 +++++++++++++++-------------
> 2 files changed, 21 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index 0e47465ef0fd..650874b400b5 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -10,6 +10,7 @@
> #include <linux/xattr.h>
> #include <linux/fs_parser.h>
> #include <linux/userfaultfd_k.h>
> +#include <linux/bits.h>
>
> struct swap_iocb;
>
> @@ -19,6 +20,11 @@ struct swap_iocb;
> #define SHMEM_MAXQUOTAS 2
> #endif
>
> +/* Suppress pre-accounting of the entire object size. */
> +#define SHMEM_F_NORESERVE BIT(0)
> +/* Disallow swapping. */
> +#define SHMEM_F_LOCKED BIT(1)
> +
> struct shmem_inode_info {
> spinlock_t lock;
> unsigned int seals; /* shmem seals */
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 58701d14dd96..1d5036dec08a 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -175,20 +175,20 @@ static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
> */
> static inline int shmem_acct_size(unsigned long flags, loff_t size)
> {
> - return (flags & VM_NORESERVE) ?
> + return (flags & SHMEM_F_NORESERVE) ?
> 0 : security_vm_enough_memory_mm(current->mm, VM_ACCT(size));
> }
>
> static inline void shmem_unacct_size(unsigned long flags, loff_t size)
> {
> - if (!(flags & VM_NORESERVE))
> + if (!(flags & SHMEM_F_NORESERVE))
> vm_unacct_memory(VM_ACCT(size));
> }
>
> static inline int shmem_reacct_size(unsigned long flags,
> loff_t oldsize, loff_t newsize)
> {
> - if (!(flags & VM_NORESERVE)) {
> + if (!(flags & SHMEM_F_NORESERVE)) {
> if (VM_ACCT(newsize) > VM_ACCT(oldsize))
> return security_vm_enough_memory_mm(current->mm,
> VM_ACCT(newsize) - VM_ACCT(oldsize));
> @@ -206,7 +206,7 @@ static inline int shmem_reacct_size(unsigned long flags,
> */
> static inline int shmem_acct_blocks(unsigned long flags, long pages)
> {
> - if (!(flags & VM_NORESERVE))
> + if (!(flags & SHMEM_F_NORESERVE))
> return 0;
>
> return security_vm_enough_memory_mm(current->mm,
> @@ -215,7 +215,7 @@ static inline int shmem_acct_blocks(unsigned long flags, long pages)
>
> static inline void shmem_unacct_blocks(unsigned long flags, long pages)
> {
> - if (flags & VM_NORESERVE)
> + if (flags & SHMEM_F_NORESERVE)
> vm_unacct_memory(pages * VM_ACCT(PAGE_SIZE));
> }
>
> @@ -1551,7 +1551,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
> int nr_pages;
> bool split = false;
>
> - if ((info->flags & VM_LOCKED) || sbinfo->noswap)
> + if ((info->flags & SHMEM_F_LOCKED) || sbinfo->noswap)
> goto redirty;
>
> if (!total_swap_pages)
> @@ -2910,15 +2910,15 @@ int shmem_lock(struct file *file, int lock, struct ucounts *ucounts)
> * ipc_lock_object() when called from shmctl_do_lock(),
> * no serialization needed when called from shm_destroy().
> */
> - if (lock && !(info->flags & VM_LOCKED)) {
> + if (lock && !(info->flags & SHMEM_F_LOCKED)) {
> if (!user_shm_lock(inode->i_size, ucounts))
> goto out_nomem;
> - info->flags |= VM_LOCKED;
> + info->flags |= SHMEM_F_LOCKED;
> mapping_set_unevictable(file->f_mapping);
> }
> - if (!lock && (info->flags & VM_LOCKED) && ucounts) {
> + if (!lock && (info->flags & SHMEM_F_LOCKED) && ucounts) {
> user_shm_unlock(inode->i_size, ucounts);
> - info->flags &= ~VM_LOCKED;
> + info->flags &= ~SHMEM_F_LOCKED;
> mapping_clear_unevictable(file->f_mapping);
> }
> retval = 0;
> @@ -3062,7 +3062,7 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
> spin_lock_init(&info->lock);
> atomic_set(&info->stop_eviction, 0);
> info->seals = F_SEAL_SEAL;
> - info->flags = flags & VM_NORESERVE;
> + info->flags = (flags & VM_NORESERVE) ? SHMEM_F_NORESERVE : 0;
> info->i_crtime = inode_get_mtime(inode);
> info->fsflags = (dir == NULL) ? 0 :
> SHMEM_I(dir)->fsflags & SHMEM_FL_INHERITED;
> @@ -5804,8 +5804,10 @@ static inline struct inode *shmem_get_inode(struct mnt_idmap *idmap,
> /* common code */
>
> static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name,
> - loff_t size, unsigned long flags, unsigned int i_flags)
> + loff_t size, unsigned long vm_flags,
> + unsigned int i_flags)
> {
> + unsigned long flags = (vm_flags & VM_NORESERVE) ? SHMEM_F_NORESERVE : 0;
> struct inode *inode;
> struct file *res;
>
> @@ -5822,7 +5824,7 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name,
> return ERR_PTR(-ENOMEM);
>
> inode = shmem_get_inode(&nop_mnt_idmap, mnt->mnt_sb, NULL,
> - S_IFREG | S_IRWXUGO, 0, flags);
> + S_IFREG | S_IRWXUGO, 0, vm_flags);
> if (IS_ERR(inode)) {
> shmem_unacct_size(flags, size);
> return ERR_CAST(inode);
> --
> 2.52.0.rc1.455.g30608eb744-goog
>
--
Sincerely yours,
Mike.
^ permalink raw reply
* Re: [PATCH v6 12/20] mm: shmem: allow freezing inode mapping
From: Mike Rapoport @ 2025-11-17 10:08 UTC (permalink / raw)
To: Pasha Tatashin
Cc: pratyush, jasonmiu, graf, dmatlack, rientjes, corbet, rdunlap,
ilpo.jarvinen, kanie, ojeda, aliceryhl, masahiroy, akpm, tj,
yoann.congal, mmaurer, roman.gushchin, chenridong, axboe,
mark.rutland, jannh, vincent.guittot, hannes, dan.j.williams,
david, joel.granados, rostedt, anna.schumaker, song, linux,
linux-kernel, linux-doc, linux-mm, gregkh, tglx, mingo, bp,
dave.hansen, x86, hpa, rafael, dakr, bartosz.golaszewski,
cw00.choi, myungjoo.ham, yesanishhere, Jonathan.Cameron,
quic_zijuhu, aleksander.lobakin, ira.weiny, andriy.shevchenko,
leon, lukas, bhelgaas, wagi, djeffery, stuart.w.hayes, ptyadav,
lennart, brauner, linux-api, linux-fsdevel, saeedm, ajayachandra,
jgg, parav, leonro, witu, hughd, skhawaja, chrisl
In-Reply-To: <20251115233409.768044-13-pasha.tatashin@soleen.com>
On Sat, Nov 15, 2025 at 06:33:58PM -0500, Pasha Tatashin wrote:
> From: Pratyush Yadav <ptyadav@amazon.de>
>
> To prepare a shmem inode for live update via the Live Update
> Orchestrator (LUO), its index -> folio mappings must be serialized. Once
> the mappings are serialized, they cannot change since it would cause the
> serialized data to become inconsistent. This can be done by pinning the
> folios to avoid migration, and by making sure no folios can be added to
> or removed from the inode.
>
> While mechanisms to pin folios already exist, the only way to stop
> folios being added or removed are the grow and shrink file seals. But
> file seals come with their own semantics, one of which is that they
> can't be removed. This doesn't work with liveupdate since it can be
> cancelled or error out, which would need the seals to be removed and the
> file's normal functionality to be restored.
>
> Introduce SHMEM_F_MAPPING_FROZEN to indicate this instead. It is
> internal to shmem and is not directly exposed to userspace. It functions
> similar to F_SEAL_GROW | F_SEAL_SHRINK, but additionally disallows hole
> punching, and can be removed.
>
> Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> include/linux/shmem_fs.h | 17 +++++++++++++++++
> mm/shmem.c | 12 +++++++++++-
> 2 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index 650874b400b5..a9f5db472a39 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -24,6 +24,14 @@ struct swap_iocb;
> #define SHMEM_F_NORESERVE BIT(0)
> /* Disallow swapping. */
> #define SHMEM_F_LOCKED BIT(1)
> +/*
> + * Disallow growing, shrinking, or hole punching in the inode. Combined with
> + * folio pinning, makes sure the inode's mapping stays fixed.
> + *
> + * In some ways similar to F_SEAL_GROW | F_SEAL_SHRINK, but can be removed and
> + * isn't directly visible to userspace.
> + */
> +#define SHMEM_F_MAPPING_FROZEN BIT(2)
>
> struct shmem_inode_info {
> spinlock_t lock;
> @@ -186,6 +194,15 @@ static inline bool shmem_file(struct file *file)
> return shmem_mapping(file->f_mapping);
> }
>
> +/* Must be called with inode lock taken exclusive. */
> +static inline void shmem_i_mapping_freeze(struct inode *inode, bool freeze)
_mapping usually refers to operations on struct address_space.
It seems that all shmem methods that take inode are just shmem_<operation>,
so shmem_freeze() looks more appropriate.
> +{
> + if (freeze)
> + SHMEM_I(inode)->flags |= SHMEM_F_MAPPING_FROZEN;
> + else
> + SHMEM_I(inode)->flags &= ~SHMEM_F_MAPPING_FROZEN;
> +}
> +
> /*
> * If fallocate(FALLOC_FL_KEEP_SIZE) has been used, there may be pages
> * beyond i_size's notion of EOF, which fallocate has committed to reserving:
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 1d5036dec08a..05c3db840257 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1292,7 +1292,8 @@ static int shmem_setattr(struct mnt_idmap *idmap,
> loff_t newsize = attr->ia_size;
>
> /* protected by i_rwsem */
> - if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
> + if ((info->flags & SHMEM_F_MAPPING_FROZEN) ||
A corner case: if newsize == oldsize this will be a false positive
> + (newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
> (newsize > oldsize && (info->seals & F_SEAL_GROW)))
> return -EPERM;
>
> @@ -3289,6 +3290,10 @@ shmem_write_begin(const struct kiocb *iocb, struct address_space *mapping,
> return -EPERM;
> }
>
> + if (unlikely((info->flags & SHMEM_F_MAPPING_FROZEN) &&
> + pos + len > inode->i_size))
> + return -EPERM;
> +
> ret = shmem_get_folio(inode, index, pos + len, &folio, SGP_WRITE);
> if (ret)
> return ret;
> @@ -3662,6 +3667,11 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
>
> inode_lock(inode);
>
> + if (info->flags & SHMEM_F_MAPPING_FROZEN) {
> + error = -EPERM;
> + goto out;
> + }
> +
> if (mode & FALLOC_FL_PUNCH_HOLE) {
> struct address_space *mapping = file->f_mapping;
> loff_t unmap_start = round_up(offset, PAGE_SIZE);
> --
> 2.52.0.rc1.455.g30608eb744-goog
>
--
Sincerely yours,
Mike.
^ permalink raw reply
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