[PATCH RFC V10 0/7] Add NUMA mempolicy support for KVM guest-memfd

[PATCH RFC V10 0/7] Add NUMA mempolicy support for KVM guest-memfd

[Shivank Garg]

This series introduces NUMA-aware memory placement support for KVM guests
with guest_memfd memory backends. It builds upon Fuad Tabba's work (V17)
that enabled host-mapping for guest_memfd memory [1].

== Background == 
KVM's guest-memfd memory backend currently lacks support for NUMA policy
enforcement, causing guest memory allocations to be distributed across host
nodes  according to kernel's default behavior, irrespective of any policy
specified by the VMM. This limitation arises because conventional userspace
NUMA control mechanisms like mbind(2) don't work since the memory isn't
directly mapped to userspace when allocations occur.
Fuad's work [1] provides the necessary mmap capability, and this series
leverages it to enable mbind(2).

== Implementation ==
This series implements proper NUMA policy support for guest-memfd by:

1. Adding mempolicy-aware allocation APIs to the filemap layer.
2. Introducing custom inodes (via a dedicated slab-allocated inode cache,
   kvm_gmem_inode_info) to store NUMA policy and metadata for guest memory.
3. Implementing get/set_policy vm_ops in guest_memfd to support NUMA
   policy.

With these changes, VMMs can now control guest memory placement by mapping
guest_memfd file descriptor and using mbind(2) to specify:
- Policy modes: default, bind, interleave, or preferred
- Host NUMA nodes: List of target nodes for memory allocation

These Policies affect only future allocations and do not migrate existing
memory. This matches mbind(2)'s default behavior which affects only new
allocations unless overridden with MPOL_MF_MOVE/MPOL_MF_MOVE_ALL flags (Not
supported for guest_memfd as it is unmovable by design).

== Upstream Plan ==
Phased approach as per David's guest_memfd extension overview [2] and
community calls [3]:

Phase 1 (this series):
1. Focuses on shared guest_memfd support (non-CoCo VMs).
2. Builds on Fuad's host-mapping work.

Phase2 (future work):
1. NUMA support for private guest_memfd (CoCo VMs).
2. Depends on SNP in-place conversion support [4].

This series provides a clean integration path for NUMA-aware memory
management for guest_memfd and lays the groundwork for future confidential
computing NUMA capabilities.

Please review and provide feedback!

Thanks,
Shivank

== Changelog ==

- v1,v2: Extended the KVM_CREATE_GUEST_MEMFD IOCTL to pass mempolicy.
- v3: Introduced fbind() syscall for VMM memory-placement configuration.
- v4-v6: Current approach using shared_policy support and vm_ops (based on
         suggestions from David [5] and guest_memfd bi-weekly upstream
         call discussion [6]).
- v7: Use inodes to store NUMA policy instead of file [7].
- v8: Rebase on top of Fuad's V12: Host mmaping for guest_memfd memory.
- v9: Rebase on top of Fuad's V13 and incorporate review comments
- V10: Rebase on top of Fuad's V17. Use latest guest_memfd inode patch
       from Ackerley (with David's review comments). Use newer kmem_cache_create()
       API variant with arg parameter (Vlastimil)

[1] https://lore.kernel.org/all/20250729225455.670324-1-seanjc@google.com
[2] https://lore.kernel.org/all/c1c9591d-218a-495c-957b-ba356c8f8e09@redhat.com
[3] https://docs.google.com/document/d/1M6766BzdY1Lhk7LiR5IqVR8B8mG3cr-cxTxOrAosPOk/edit?tab=t.0#heading=h.svcbod20b5ur
[4] https://lore.kernel.org/all/20250613005400.3694904-1-michael.roth@amd.com
[5] https://lore.kernel.org/all/6fbef654-36e2-4be5-906e-2a648a845278@redhat.com
[6] https://lore.kernel.org/all/2b77e055-98ac-43a1-a7ad-9f9065d7f38f@amd.com
[7] https://lore.kernel.org/all/diqzbjumm167.fsf@ackerleytng-ctop.c.googlers.com

Ackerley Tng (1):
  KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes

Matthew Wilcox (Oracle) (2):
  mm/filemap: Add NUMA mempolicy support to filemap_alloc_folio()
  mm/filemap: Extend __filemap_get_folio() to support NUMA memory
    policies

Shivank Garg (4):
  mm/mempolicy: Export memory policy symbols
  KVM: guest_memfd: Add slab-allocated inode cache
  KVM: guest_memfd: Enforce NUMA mempolicy using shared policy
  KVM: guest_memfd: selftests: Add tests for mmap and NUMA policy
    support

 fs/bcachefs/fs-io-buffered.c                  |   2 +-
 fs/btrfs/compression.c                        |   4 +-
 fs/btrfs/verity.c                             |   2 +-
 fs/erofs/zdata.c                              |   2 +-
 fs/f2fs/compress.c                            |   2 +-
 include/linux/pagemap.h                       |  18 +-
 include/uapi/linux/magic.h                    |   1 +
 mm/filemap.c                                  |  23 +-
 mm/mempolicy.c                                |   6 +
 mm/readahead.c                                |   2 +-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/guest_memfd_test.c  | 121 ++++++++
 virt/kvm/guest_memfd.c                        | 260 ++++++++++++++++--
 virt/kvm/kvm_main.c                           |   7 +-
 virt/kvm/kvm_mm.h                             |   9 +-
 15 files changed, 410 insertions(+), 50 deletions(-)

-- 
2.43.0

[PATCH RFC V10 1/7] mm/filemap: Add NUMA mempolicy support to filemap_alloc_folio()

[Shivank Garg]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Add a mempolicy parameter to filemap_alloc_folio() to enable NUMA-aware
page cache allocations. This will be used by upcoming changes to
support NUMA policies in guest-memfd, where guest_memory need to be
allocated NUMA policy specified by VMM.

All existing users pass NULL maintaining current behavior.

Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 fs/bcachefs/fs-io-buffered.c |  2 +-
 fs/btrfs/compression.c       |  4 ++--
 fs/btrfs/verity.c            |  2 +-
 fs/erofs/zdata.c             |  2 +-
 fs/f2fs/compress.c           |  2 +-
 include/linux/pagemap.h      |  8 +++++---
 mm/filemap.c                 | 14 +++++++++-----
 mm/readahead.c               |  2 +-
 8 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/fs/bcachefs/fs-io-buffered.c b/fs/bcachefs/fs-io-buffered.c
index 1c54b9b5bd69..3af2eabb7ed3 100644
--- a/fs/bcachefs/fs-io-buffered.c
+++ b/fs/bcachefs/fs-io-buffered.c
@@ -124,7 +124,7 @@ static int readpage_bio_extend(struct btree_trans *trans,
 			if (folio && !xa_is_value(folio))
 				break;
 
-			folio = filemap_alloc_folio(readahead_gfp_mask(iter->mapping), order);
+			folio = filemap_alloc_folio(readahead_gfp_mask(iter->mapping), order, NULL);
 			if (!folio)
 				break;
 
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index d09d622016ef..139f9609e737 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -474,8 +474,8 @@ static noinline int add_ra_bio_pages(struct inode *inode,
 			continue;
 		}
 
-		folio = filemap_alloc_folio(mapping_gfp_constraint(mapping,
-								   ~__GFP_FS), 0);
+		folio = filemap_alloc_folio(mapping_gfp_constraint(mapping, ~__GFP_FS),
+					    0, NULL);
 		if (!folio)
 			break;
 
diff --git a/fs/btrfs/verity.c b/fs/btrfs/verity.c
index b7a96a005487..c43a789ba6d2 100644
--- a/fs/btrfs/verity.c
+++ b/fs/btrfs/verity.c
@@ -742,7 +742,7 @@ static struct page *btrfs_read_merkle_tree_page(struct inode *inode,
 	}
 
 	folio = filemap_alloc_folio(mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS),
-				    0);
+				    0, NULL);
 	if (!folio)
 		return ERR_PTR(-ENOMEM);
 
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 792f20888a8f..09e2ed2ae0d1 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -562,7 +562,7 @@ static void z_erofs_bind_cache(struct z_erofs_frontend *fe)
 			 * Allocate a managed folio for cached I/O, or it may be
 			 * then filled with a file-backed folio for in-place I/O
 			 */
-			newfolio = filemap_alloc_folio(gfp, 0);
+			newfolio = filemap_alloc_folio(gfp, 0, NULL);
 			if (!newfolio)
 				continue;
 			newfolio->private = Z_EROFS_PREALLOCATED_FOLIO;
diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 5c1f47e45dab..56a51c9ba4f1 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1942,7 +1942,7 @@ static void f2fs_cache_compressed_page(struct f2fs_sb_info *sbi,
 		return;
 	}
 
-	cfolio = filemap_alloc_folio(__GFP_NOWARN | __GFP_IO, 0);
+	cfolio = filemap_alloc_folio(__GFP_NOWARN | __GFP_IO, 0, NULL);
 	if (!cfolio)
 		return;
 
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 12a12dae727d..ce617a35dc35 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -646,9 +646,11 @@ static inline void *detach_page_private(struct page *page)
 }
 
 #ifdef CONFIG_NUMA
-struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order);
+struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order,
+		struct mempolicy *policy);
 #else
-static inline struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order)
+static inline struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order,
+		struct mempolicy *policy)
 {
 	return folio_alloc_noprof(gfp, order);
 }
@@ -659,7 +661,7 @@ static inline struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int o
 
 static inline struct page *__page_cache_alloc(gfp_t gfp)
 {
-	return &filemap_alloc_folio(gfp, 0)->page;
+	return &filemap_alloc_folio(gfp, 0, NULL)->page;
 }
 
 static inline gfp_t readahead_gfp_mask(struct address_space *x)
diff --git a/mm/filemap.c b/mm/filemap.c
index 751838ef05e5..495f7f5c3d2e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -989,11 +989,16 @@ int filemap_add_folio(struct address_space *mapping, struct folio *folio,
 EXPORT_SYMBOL_GPL(filemap_add_folio);
 
 #ifdef CONFIG_NUMA
-struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order)
+struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order,
+		struct mempolicy *policy)
 {
 	int n;
 	struct folio *folio;
 
+	if (policy)
+		return folio_alloc_mpol_noprof(gfp, order, policy,
+				NO_INTERLEAVE_INDEX, numa_node_id());
+
 	if (cpuset_do_page_mem_spread()) {
 		unsigned int cpuset_mems_cookie;
 		do {
@@ -1978,7 +1983,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			err = -ENOMEM;
 			if (order > min_order)
 				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
-			folio = filemap_alloc_folio(alloc_gfp, order);
+			folio = filemap_alloc_folio(alloc_gfp, order, NULL);
 			if (!folio)
 				continue;
 
@@ -2517,7 +2522,7 @@ static int filemap_create_folio(struct kiocb *iocb, struct folio_batch *fbatch)
 	if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
 		return -EAGAIN;
 
-	folio = filemap_alloc_folio(mapping_gfp_mask(mapping), min_order);
+	folio = filemap_alloc_folio(mapping_gfp_mask(mapping), min_order, NULL);
 	if (!folio)
 		return -ENOMEM;
 	if (iocb->ki_flags & IOCB_DONTCACHE)
@@ -3916,8 +3921,7 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
 repeat:
 	folio = filemap_get_folio(mapping, index);
 	if (IS_ERR(folio)) {
-		folio = filemap_alloc_folio(gfp,
-					    mapping_min_folio_order(mapping));
+		folio = filemap_alloc_folio(gfp, mapping_min_folio_order(mapping), NULL);
 		if (!folio)
 			return ERR_PTR(-ENOMEM);
 		index = mapping_align_index(mapping, index);
diff --git a/mm/readahead.c b/mm/readahead.c
index 406756d34309..a4dfa837dfbd 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -183,7 +183,7 @@ static struct folio *ractl_alloc_folio(struct readahead_control *ractl,
 {
 	struct folio *folio;
 
-	folio = filemap_alloc_folio(gfp_mask, order);
+	folio = filemap_alloc_folio(gfp_mask, order, NULL);
 	if (folio && ractl->dropbehind)
 		__folio_set_dropbehind(folio);
 
-- 
2.43.0

[PATCH RFC V10 2/7] mm/filemap: Extend __filemap_get_folio() to support NUMA memory policies

[Shivank Garg]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Extend __filemap_get_folio() to support NUMA memory policies by
renaming the implementation to __filemap_get_folio_mpol() and adding
a mempolicy parameter. The original function becomes a static inline
wrapper that passes NULL for the mempolicy.

This infrastructure will enable future support for NUMA-aware page cache
allocations in guest_memfd memory backend KVM guests.

Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 include/linux/pagemap.h | 10 ++++++++--
 mm/filemap.c            | 11 ++++++-----
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ce617a35dc35..94d65ced0a1d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -747,11 +747,17 @@ static inline fgf_t fgf_set_order(size_t size)
 }
 
 void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
-struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
-		fgf_t fgp_flags, gfp_t gfp);
+struct folio *__filemap_get_folio_mpol(struct address_space *mapping,
+		pgoff_t index, fgf_t fgf_flags, gfp_t gfp, struct mempolicy *policy);
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
 		fgf_t fgp_flags, gfp_t gfp);
 
+static inline struct folio *__filemap_get_folio(struct address_space *mapping,
+		pgoff_t index, fgf_t fgf_flags, gfp_t gfp)
+{
+	return __filemap_get_folio_mpol(mapping, index, fgf_flags, gfp, NULL);
+}
+
 /**
  * write_begin_get_folio - Get folio for write_begin with flags.
  * @iocb: The kiocb passed from write_begin (may be NULL).
diff --git a/mm/filemap.c b/mm/filemap.c
index 495f7f5c3d2e..03f223be575c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1897,11 +1897,12 @@ void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
 }
 
 /**
- * __filemap_get_folio - Find and get a reference to a folio.
+ * __filemap_get_folio_mpol - Find and get a reference to a folio.
  * @mapping: The address_space to search.
  * @index: The page index.
  * @fgp_flags: %FGP flags modify how the folio is returned.
  * @gfp: Memory allocation flags to use if %FGP_CREAT is specified.
+ * @policy: NUMA memory allocation policy to follow.
  *
  * Looks up the page cache entry at @mapping & @index.
  *
@@ -1912,8 +1913,8 @@ void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
  *
  * Return: The found folio or an ERR_PTR() otherwise.
  */
-struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
-		fgf_t fgp_flags, gfp_t gfp)
+struct folio *__filemap_get_folio_mpol(struct address_space *mapping,
+		pgoff_t index, fgf_t fgp_flags, gfp_t gfp, struct mempolicy *policy)
 {
 	struct folio *folio;
 
@@ -1983,7 +1984,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			err = -ENOMEM;
 			if (order > min_order)
 				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
-			folio = filemap_alloc_folio(alloc_gfp, order, NULL);
+			folio = filemap_alloc_folio(alloc_gfp, order, policy);
 			if (!folio)
 				continue;
 
@@ -2030,7 +2031,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		folio_clear_dropbehind(folio);
 	return folio;
 }
-EXPORT_SYMBOL(__filemap_get_folio);
+EXPORT_SYMBOL(__filemap_get_folio_mpol);
 
 static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
 		xa_mark_t mark)
-- 
2.43.0

[PATCH RFC V10 3/7] mm/mempolicy: Export memory policy symbols

[Shivank Garg]

KVM guest_memfd wants to implement support for NUMA policies just like
shmem already does using the shared policy infrastructure. As
guest_memfd currently resides in KVM module code, we have to export the
relevant symbols.

In the future, guest_memfd might be moved to core-mm, at which point the
symbols no longer would have to be exported. When/if that happens is
still unclear.

Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 mm/mempolicy.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index eb83cff7db8c..d385202306db 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -354,6 +354,7 @@ struct mempolicy *get_task_policy(struct task_struct *p)
 
 	return &default_policy;
 }
+EXPORT_SYMBOL_GPL_FOR_MODULES(get_task_policy, "kvm");
 
 static const struct mempolicy_operations {
 	int (*create)(struct mempolicy *pol, const nodemask_t *nodes);
@@ -487,6 +488,7 @@ void __mpol_put(struct mempolicy *pol)
 		return;
 	kmem_cache_free(policy_cache, pol);
 }
+EXPORT_SYMBOL_GPL_FOR_MODULES(__mpol_put, "kvm");
 
 static void mpol_rebind_default(struct mempolicy *pol, const nodemask_t *nodes)
 {
@@ -2885,6 +2887,7 @@ struct mempolicy *mpol_shared_policy_lookup(struct shared_policy *sp,
 	read_unlock(&sp->lock);
 	return pol;
 }
+EXPORT_SYMBOL_GPL_FOR_MODULES(mpol_shared_policy_lookup, "kvm");
 
 static void sp_free(struct sp_node *n)
 {
@@ -3170,6 +3173,7 @@ void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol)
 		mpol_put(mpol);	/* drop our incoming ref on sb mpol */
 	}
 }
+EXPORT_SYMBOL_GPL_FOR_MODULES(mpol_shared_policy_init, "kvm");
 
 int mpol_set_shared_policy(struct shared_policy *sp,
 			struct vm_area_struct *vma, struct mempolicy *pol)
@@ -3188,6 +3192,7 @@ int mpol_set_shared_policy(struct shared_policy *sp,
 		sp_free(new);
 	return err;
 }
+EXPORT_SYMBOL_GPL_FOR_MODULES(mpol_set_shared_policy, "kvm");
 
 /* Free a backing policy store on inode delete. */
 void mpol_free_shared_policy(struct shared_policy *sp)
@@ -3206,6 +3211,7 @@ void mpol_free_shared_policy(struct shared_policy *sp)
 	}
 	write_unlock(&sp->lock);
 }
+EXPORT_SYMBOL_GPL_FOR_MODULES(mpol_free_shared_policy, "kvm");
 
 #ifdef CONFIG_NUMA_BALANCING
 static int __initdata numabalancing_override;
-- 
2.43.0

[PATCH RFC V10 4/7] KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes

[Shivank Garg]

From: Ackerley Tng <ackerleytng@google.com>

guest_memfd's inode represents memory the guest_memfd is
providing. guest_memfd's file represents a struct kvm's view of that
memory.

Using a custom inode allows customization of the inode teardown
process via callbacks. For example, ->evict_inode() allows
customization of the truncation process on file close, and
->destroy_inode() and ->free_inode() allow customization of the inode
freeing process.

Customizing the truncation process allows flexibility in management of
guest_memfd memory and customization of the inode freeing process
allows proper cleanup of memory metadata stored on the inode.

Memory metadata is more appropriately stored on the inode (as opposed
to the file), since the metadata is for the memory and is not unique
to a specific binding and struct kvm.

Co-developed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 include/uapi/linux/magic.h |   1 +
 virt/kvm/guest_memfd.c     | 128 ++++++++++++++++++++++++++++++-------
 virt/kvm/kvm_main.c        |   7 +-
 virt/kvm/kvm_mm.h          |   9 +--
 4 files changed, 118 insertions(+), 27 deletions(-)

diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index bb575f3ab45e..638ca21b7a90 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -103,5 +103,6 @@
 #define DEVMEM_MAGIC		0x454d444d	/* "DMEM" */
 #define SECRETMEM_MAGIC		0x5345434d	/* "SECM" */
 #define PID_FS_MAGIC		0x50494446	/* "PIDF" */
+#define GUEST_MEMFD_MAGIC	0x474d454d	/* "GMEM" */
 
 #endif /* __LINUX_MAGIC_H__ */
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 08a6bc7d25b6..0e93323fc839 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1,12 +1,16 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/anon_inodes.h>
 #include <linux/backing-dev.h>
 #include <linux/falloc.h>
+#include <linux/fs.h>
 #include <linux/kvm_host.h>
+#include <linux/pseudo_fs.h>
 #include <linux/pagemap.h>
-#include <linux/anon_inodes.h>
 
 #include "kvm_mm.h"
 
+static struct vfsmount *kvm_gmem_mnt;
+
 struct kvm_gmem {
 	struct kvm *kvm;
 	struct xarray bindings;
@@ -385,9 +389,45 @@ static struct file_operations kvm_gmem_fops = {
 	.fallocate	= kvm_gmem_fallocate,
 };
 
-void kvm_gmem_init(struct module *module)
+static int kvm_gmem_init_fs_context(struct fs_context *fc)
+{
+	if (!init_pseudo(fc, GUEST_MEMFD_MAGIC))
+		return -ENOMEM;
+
+	fc->s_iflags |= SB_I_NOEXEC;
+	fc->s_iflags |= SB_I_NODEV;
+
+	return 0;
+}
+
+static struct file_system_type kvm_gmem_fs = {
+	.name		 = "guest_memfd",
+	.init_fs_context = kvm_gmem_init_fs_context,
+	.kill_sb	 = kill_anon_super,
+};
+
+static int kvm_gmem_init_mount(void)
+{
+	kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);
+
+	if (IS_ERR(kvm_gmem_mnt))
+		return PTR_ERR(kvm_gmem_mnt);
+
+	kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;
+	return 0;
+}
+
+int kvm_gmem_init(struct module *module)
 {
 	kvm_gmem_fops.owner = module;
+
+	return kvm_gmem_init_mount();
+}
+
+void kvm_gmem_exit(void)
+{
+	kern_unmount(kvm_gmem_mnt);
+	kvm_gmem_mnt = NULL;
 }
 
 static int kvm_gmem_migrate_folio(struct address_space *mapping,
@@ -463,11 +503,71 @@ bool __weak kvm_arch_supports_gmem_mmap(struct kvm *kvm)
 	return true;
 }
 
+static struct inode *kvm_gmem_inode_make_secure_inode(const char *name,
+						      loff_t size, u64 flags)
+{
+	struct inode *inode;
+
+	inode = anon_inode_make_secure_inode(kvm_gmem_mnt->mnt_sb, name, NULL);
+	if (IS_ERR(inode))
+		return inode;
+
+	inode->i_private = (void *)(unsigned long)flags;
+	inode->i_op = &kvm_gmem_iops;
+	inode->i_mapping->a_ops = &kvm_gmem_aops;
+	inode->i_mode |= S_IFREG;
+	inode->i_size = size;
+	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
+	mapping_set_inaccessible(inode->i_mapping);
+	/* Unmovable mappings are supposed to be marked unevictable as well. */
+	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
+
+	return inode;
+}
+
+static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
+						  u64 flags)
+{
+	static const char *name = "[kvm-gmem]";
+	struct inode *inode;
+	struct file *file;
+	int err;
+
+	err = -ENOENT;
+	if (!try_module_get(kvm_gmem_fops.owner))
+		goto err;
+
+	inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
+	if (IS_ERR(inode)) {
+		err = PTR_ERR(inode);
+		goto err_put_module;
+	}
+
+	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
+				 &kvm_gmem_fops);
+	if (IS_ERR(file)) {
+		err = PTR_ERR(file);
+		goto err_put_inode;
+	}
+
+	file->f_flags |= O_LARGEFILE;
+	file->private_data = priv;
+
+out:
+	return file;
+
+err_put_inode:
+	iput(inode);
+err_put_module:
+	module_put(kvm_gmem_fops.owner);
+err:
+	file = ERR_PTR(err);
+	goto out;
+}
+
 static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 {
-	const char *anon_name = "[kvm-gmem]";
 	struct kvm_gmem *gmem;
-	struct inode *inode;
 	struct file *file;
 	int fd, err;
 
@@ -481,32 +581,16 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 		goto err_fd;
 	}
 
-	file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem,
-					 O_RDWR, NULL);
+	file = kvm_gmem_inode_create_getfile(gmem, size, flags);
 	if (IS_ERR(file)) {
 		err = PTR_ERR(file);
 		goto err_gmem;
 	}
 
-	file->f_flags |= O_LARGEFILE;
-
-	inode = file->f_inode;
-	WARN_ON(file->f_mapping != inode->i_mapping);
-
-	inode->i_private = (void *)(unsigned long)flags;
-	inode->i_op = &kvm_gmem_iops;
-	inode->i_mapping->a_ops = &kvm_gmem_aops;
-	inode->i_mode |= S_IFREG;
-	inode->i_size = size;
-	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
-	mapping_set_inaccessible(inode->i_mapping);
-	/* Unmovable mappings are supposed to be marked unevictable as well. */
-	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
-
 	kvm_get_kvm(kvm);
 	gmem->kvm = kvm;
 	xa_init(&gmem->bindings);
-	list_add(&gmem->entry, &inode->i_mapping->i_private_list);
+	list_add(&gmem->entry, &file_inode(file)->i_mapping->i_private_list);
 
 	fd_install(fd, file);
 	return fd;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 18f29ef93543..301d48d6e00d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -6489,7 +6489,9 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
 	if (WARN_ON_ONCE(r))
 		goto err_vfio;
 
-	kvm_gmem_init(module);
+	r = kvm_gmem_init(module);
+	if (r)
+		goto err_gmem;
 
 	r = kvm_init_virtualization();
 	if (r)
@@ -6510,6 +6512,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
 err_register:
 	kvm_uninit_virtualization();
 err_virt:
+	kvm_gmem_exit();
+err_gmem:
 	kvm_vfio_ops_exit();
 err_vfio:
 	kvm_async_pf_deinit();
@@ -6541,6 +6545,7 @@ void kvm_exit(void)
 	for_each_possible_cpu(cpu)
 		free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
 	kmem_cache_destroy(kvm_vcpu_cache);
+	kvm_gmem_exit();
 	kvm_vfio_ops_exit();
 	kvm_async_pf_deinit();
 	kvm_irqfd_exit();
diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h
index 31defb08ccba..9fcc5d5b7f8d 100644
--- a/virt/kvm/kvm_mm.h
+++ b/virt/kvm/kvm_mm.h
@@ -68,17 +68,18 @@ static inline void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm,
 #endif /* HAVE_KVM_PFNCACHE */
 
 #ifdef CONFIG_KVM_GUEST_MEMFD
-void kvm_gmem_init(struct module *module);
+int kvm_gmem_init(struct module *module);
+void kvm_gmem_exit(void);
 int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args);
 int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
 		  unsigned int fd, loff_t offset);
 void kvm_gmem_unbind(struct kvm_memory_slot *slot);
 #else
-static inline void kvm_gmem_init(struct module *module)
+static inline int kvm_gmem_init(struct module *module)
 {
-
+	return 0;
 }
-
+static inline void kvm_gmem_exit(void) {};
 static inline int kvm_gmem_bind(struct kvm *kvm,
 					 struct kvm_memory_slot *slot,
 					 unsigned int fd, loff_t offset)
-- 
2.43.0

[PATCH RFC V10 5/7] KVM: guest_memfd: Add slab-allocated inode cache

[Shivank Garg]

Add dedicated inode structure (kvm_gmem_inode_info) and slab-allocated
inode cache for guest memory backing, similar to how shmem handles inodes.

This adds the necessary allocation/destruction functions and prepares
for upcoming guest_memfd NUMA policy support changes.

Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 virt/kvm/guest_memfd.c | 69 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 67 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 0e93323fc839..d9c23401e770 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -17,6 +17,15 @@ struct kvm_gmem {
 	struct list_head entry;
 };
 
+struct kvm_gmem_inode_info {
+	struct inode vfs_inode;
+};
+
+static inline struct kvm_gmem_inode_info *KVM_GMEM_I(struct inode *inode)
+{
+	return container_of(inode, struct kvm_gmem_inode_info, vfs_inode);
+}
+
 /**
  * folio_file_pfn - like folio_file_page, but return a pfn.
  * @folio: The folio which contains this index.
@@ -389,13 +398,46 @@ static struct file_operations kvm_gmem_fops = {
 	.fallocate	= kvm_gmem_fallocate,
 };
 
+static struct kmem_cache *kvm_gmem_inode_cachep;
+
+static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
+{
+	struct kvm_gmem_inode_info *info;
+
+	info = alloc_inode_sb(sb, kvm_gmem_inode_cachep, GFP_KERNEL);
+	if (!info)
+		return NULL;
+
+	return &info->vfs_inode;
+}
+
+static void kvm_gmem_destroy_inode(struct inode *inode)
+{
+}
+
+static void kvm_gmem_free_inode(struct inode *inode)
+{
+	kmem_cache_free(kvm_gmem_inode_cachep, KVM_GMEM_I(inode));
+}
+
+static const struct super_operations kvm_gmem_super_operations = {
+	.statfs		= simple_statfs,
+	.alloc_inode	= kvm_gmem_alloc_inode,
+	.destroy_inode	= kvm_gmem_destroy_inode,
+	.free_inode	= kvm_gmem_free_inode,
+};
+
 static int kvm_gmem_init_fs_context(struct fs_context *fc)
 {
+	struct pseudo_fs_context *ctx;
+
 	if (!init_pseudo(fc, GUEST_MEMFD_MAGIC))
 		return -ENOMEM;
 
 	fc->s_iflags |= SB_I_NOEXEC;
 	fc->s_iflags |= SB_I_NODEV;
+	ctx = fc->fs_private;
+	ctx->ops = &kvm_gmem_super_operations;
 
 	return 0;
 }
@@ -417,17 +459,40 @@ static int kvm_gmem_init_mount(void)
 	return 0;
 }
 
+static void kvm_gmem_init_inode(void *foo)
+{
+	struct kvm_gmem_inode_info *info = foo;
+
+	inode_init_once(&info->vfs_inode);
+}
+
 int kvm_gmem_init(struct module *module)
 {
-	kvm_gmem_fops.owner = module;
+	int ret;
+	struct kmem_cache_args args = {
+		.align = 0,
+		.ctor = kvm_gmem_init_inode,
+	};
 
-	return kvm_gmem_init_mount();
+	kvm_gmem_fops.owner = module;
+	kvm_gmem_inode_cachep = kmem_cache_create("kvm_gmem_inode_cache",
+						  sizeof(struct kvm_gmem_inode_info),
+						  &args, SLAB_ACCOUNT);
+	if (!kvm_gmem_inode_cachep)
+		return -ENOMEM;
+	ret = kvm_gmem_init_mount();
+	if (ret) {
+		kmem_cache_destroy(kvm_gmem_inode_cachep);
+		return ret;
+	}
+	return 0;
 }
 
 void kvm_gmem_exit(void)
 {
 	kern_unmount(kvm_gmem_mnt);
 	kvm_gmem_mnt = NULL;
+	kmem_cache_destroy(kvm_gmem_inode_cachep);
 }
 
 static int kvm_gmem_migrate_folio(struct address_space *mapping,
-- 
2.43.0

[PATCH RFC V10 6/7] KVM: guest_memfd: Enforce NUMA mempolicy using shared policy

[Shivank Garg]

Previously, guest-memfd allocations followed local NUMA node id in absence
of process mempolicy, resulting in arbitrary memory allocation.
Moreover, mbind() couldn't be used  by the VMM as guest memory wasn't
mapped into userspace when allocation occurred.

Enable NUMA policy support by implementing vm_ops for guest-memfd mmap
operation. This allows the VMM to map the memory and use mbind() to set the
desired NUMA policy. The policy is stored in the inode structure via
kvm_gmem_inode_info, as memory policy is a property of the memory (struct
inode) itself. The policy is then retrieved via mpol_shared_policy_lookup()
and passed to filemap_grab_folio_mpol() to ensure that allocations follow
the specified memory policy.

This enables the VMM to control guest memory NUMA placement by calling
mbind() on the mapped memory regions, providing fine-grained control over
guest memory allocation across NUMA nodes.

The policy change only affect future allocations and does not migrate
existing memory. This matches mbind(2)'s default behavior which affects
only new allocations unless overridden with MPOL_MF_MOVE/MPOL_MF_MOVE_ALL
flags, which are not supported for guest_memfd as it is unmovable.

Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 virt/kvm/guest_memfd.c | 67 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 65 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index d9c23401e770..7821c1036e49 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -4,6 +4,7 @@
 #include <linux/falloc.h>
 #include <linux/fs.h>
 #include <linux/kvm_host.h>
+#include <linux/mempolicy.h>
 #include <linux/pseudo_fs.h>
 #include <linux/pagemap.h>
 
@@ -18,6 +19,7 @@ struct kvm_gmem {
 };
 
 struct kvm_gmem_inode_info {
+	struct shared_policy policy;
 	struct inode vfs_inode;
 };
 
@@ -26,6 +28,9 @@ static inline struct kvm_gmem_inode_info *KVM_GMEM_I(struct inode *inode)
 	return container_of(inode, struct kvm_gmem_inode_info, vfs_inode);
 }
 
+static struct mempolicy *kvm_gmem_get_pgoff_policy(struct kvm_gmem_inode_info *info,
+						   pgoff_t index);
+
 /**
  * folio_file_pfn - like folio_file_page, but return a pfn.
  * @folio: The folio which contains this index.
@@ -112,7 +117,25 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
 static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
 {
 	/* TODO: Support huge pages. */
-	return filemap_grab_folio(inode->i_mapping, index);
+	struct mempolicy *policy;
+	struct folio *folio;
+
+	/*
+	 * Fast-path: See if folio is already present in mapping to avoid
+	 * policy_lookup.
+	 */
+	folio = __filemap_get_folio(inode->i_mapping, index,
+				    FGP_LOCK | FGP_ACCESSED, 0);
+	if (!IS_ERR(folio))
+		return folio;
+
+	policy = kvm_gmem_get_pgoff_policy(KVM_GMEM_I(inode), index);
+	folio = __filemap_get_folio_mpol(inode->i_mapping, index,
+					 FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
+					 mapping_gfp_mask(inode->i_mapping), policy);
+	mpol_cond_put(policy);
+
+	return folio;
 }
 
 static void kvm_gmem_invalidate_begin(struct kvm_gmem *gmem, pgoff_t start,
@@ -372,8 +395,45 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf)
 	return ret;
 }
 
+#ifdef CONFIG_NUMA
+static int kvm_gmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
+{
+	struct inode *inode = file_inode(vma->vm_file);
+
+	return mpol_set_shared_policy(&KVM_GMEM_I(inode)->policy, vma, mpol);
+}
+
+static struct mempolicy *kvm_gmem_get_policy(struct vm_area_struct *vma,
+					     unsigned long addr, pgoff_t *pgoff)
+{
+	struct inode *inode = file_inode(vma->vm_file);
+
+	*pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
+	return mpol_shared_policy_lookup(&KVM_GMEM_I(inode)->policy, *pgoff);
+}
+
+static struct mempolicy *kvm_gmem_get_pgoff_policy(struct kvm_gmem_inode_info *info,
+						   pgoff_t index)
+{
+	struct mempolicy *mpol;
+
+	mpol = mpol_shared_policy_lookup(&info->policy, index);
+	return mpol ? mpol : get_task_policy(current);
+}
+#else
+static struct mempolicy *kvm_gmem_get_pgoff_policy(struct kvm_gmem_inode_info *info,
+						   pgoff_t index)
+{
+	return NULL;
+}
+#endif /* CONFIG_NUMA */
+
 static const struct vm_operations_struct kvm_gmem_vm_ops = {
-	.fault = kvm_gmem_fault_user_mapping,
+	.fault		= kvm_gmem_fault_user_mapping,
+#ifdef CONFIG_NUMA
+	.get_policy	= kvm_gmem_get_policy,
+	.set_policy	= kvm_gmem_set_policy,
+#endif
 };
 
 static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma)
@@ -408,11 +468,14 @@ static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
 	if (!info)
 		return NULL;
 
+	mpol_shared_policy_init(&info->policy, NULL);
+
 	return &info->vfs_inode;
 }
 
 static void kvm_gmem_destroy_inode(struct inode *inode)
 {
+	mpol_free_shared_policy(&KVM_GMEM_I(inode)->policy);
 }
 
 static void kvm_gmem_free_inode(struct inode *inode)
-- 
2.43.0

[PATCH RFC V10 7/7] KVM: guest_memfd: selftests: Add tests for mmap and NUMA policy support

[Shivank Garg]

Add tests for NUMA memory policy binding and NUMA aware allocation in
guest_memfd. This extends the existing selftests by adding proper
validation for:
- KVM GMEM set_policy and get_policy() vm_ops functionality using
  mbind() and get_mempolicy()
- NUMA policy application before and after memory allocation

These tests help ensure NUMA support for guest_memfd works correctly.

Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/guest_memfd_test.c  | 121 ++++++++++++++++++
 2 files changed, 122 insertions(+)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 90f03f00cb04..c46cef2a7cd7 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -275,6 +275,7 @@ pgste-option = $(call try-run, echo 'int main(void) { return 0; }' | \
 	$(CC) -Werror -Wl$(comma)--s390-pgste -x c - -o "$$TMP",-Wl$(comma)--s390-pgste)
 
 LDLIBS += -ldl
+LDLIBS += -lnuma
 LDFLAGS += -pthread $(no-pie-option) $(pgste-option)
 
 LIBKVM_C := $(filter %.c,$(LIBKVM))
diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index b86bf89a71e0..4d33c225d9f7 100644
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -7,6 +7,8 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <numa.h>
+#include <numaif.h>
 #include <errno.h>
 #include <stdio.h>
 #include <fcntl.h>
@@ -19,6 +21,7 @@
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/syscall.h>
 
 #include "kvm_util.h"
 #include "test_util.h"
@@ -72,6 +75,122 @@ static void test_mmap_supported(int fd, size_t page_size, size_t total_size)
 	TEST_ASSERT(!ret, "munmap() should succeed.");
 }
 
+#define TEST_REQUIRE_NUMA_MULTIPLE_NODES()	\
+	TEST_REQUIRE(numa_available() != -1 && numa_max_node() >= 1)
+
+static void test_mbind(int fd, size_t page_size, size_t total_size)
+{
+	unsigned long nodemask = 1; /* nid: 0 */
+	unsigned long maxnode = 8;
+	unsigned long get_nodemask;
+	int get_policy;
+	char *mem;
+	int ret;
+
+	TEST_REQUIRE_NUMA_MULTIPLE_NODES();
+
+	mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap for mbind test should succeed");
+
+	/* Test MPOL_INTERLEAVE policy */
+	ret = syscall(__NR_mbind, mem, page_size * 2, MPOL_INTERLEAVE,
+		      &nodemask, maxnode, 0);
+	TEST_ASSERT(!ret, "mbind with INTERLEAVE to node 0 should succeed");
+	ret = syscall(__NR_get_mempolicy, &get_policy, &get_nodemask,
+		      maxnode, mem, MPOL_F_ADDR);
+	TEST_ASSERT(!ret && get_policy == MPOL_INTERLEAVE && get_nodemask == nodemask,
+		    "Policy should be MPOL_INTERLEAVE and nodes match");
+
+	/* Test basic MPOL_BIND policy */
+	ret = syscall(__NR_mbind, mem + page_size * 2, page_size * 2, MPOL_BIND,
+		      &nodemask, maxnode, 0);
+	TEST_ASSERT(!ret, "mbind with MPOL_BIND to node 0 should succeed");
+	ret = syscall(__NR_get_mempolicy, &get_policy, &get_nodemask,
+		      maxnode, mem + page_size * 2, MPOL_F_ADDR);
+	TEST_ASSERT(!ret && get_policy == MPOL_BIND && get_nodemask == nodemask,
+		    "Policy should be MPOL_BIND and nodes match");
+
+	/* Test MPOL_DEFAULT policy */
+	ret = syscall(__NR_mbind, mem, total_size, MPOL_DEFAULT, NULL, 0, 0);
+	TEST_ASSERT(!ret, "mbind with MPOL_DEFAULT should succeed");
+	ret = syscall(__NR_get_mempolicy, &get_policy, &get_nodemask,
+		      maxnode, mem, MPOL_F_ADDR);
+	TEST_ASSERT(!ret && get_policy == MPOL_DEFAULT && get_nodemask == 0,
+		    "Policy should be MPOL_DEFAULT and nodes zero");
+
+	/* Test with invalid policy */
+	ret = syscall(__NR_mbind, mem, page_size, 999, &nodemask, maxnode, 0);
+	TEST_ASSERT(ret == -1 && errno == EINVAL,
+		    "mbind with invalid policy should fail with EINVAL");
+
+	TEST_ASSERT(munmap(mem, total_size) == 0, "munmap should succeed");
+}
+
+static void test_numa_allocation(int fd, size_t page_size, size_t total_size)
+{
+	unsigned long node0_mask = 1;  /* Node 0 */
+	unsigned long node1_mask = 2;  /* Node 1 */
+	unsigned long maxnode = 8;
+	void *pages[4];
+	int status[4];
+	char *mem;
+	int ret, i;
+
+	TEST_REQUIRE_NUMA_MULTIPLE_NODES();
+
+	/* Clean slate: deallocate all file space, if any */
+	ret = fallocate(fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, total_size);
+	TEST_ASSERT(!ret, "fallocate(PUNCH_HOLE) should succeed");
+
+	mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap should succeed");
+
+	for (i = 0; i < 4; i++)
+		pages[i] = (char *)mem + page_size * i;
+
+	/* Set NUMA policy after allocation */
+	memset(mem, 0xaa, page_size);
+	ret = syscall(__NR_mbind, pages[0], page_size, MPOL_BIND, &node0_mask, maxnode, 0);
+	TEST_ASSERT(!ret, "mbind after allocation page 0 to node 0 should succeed");
+	ret = fallocate(fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, page_size);
+	TEST_ASSERT(!ret, "fallocate(PUNCH_HOLE) should succeed");
+
+	/* Set NUMA policy before allocation */
+	ret = syscall(__NR_mbind, pages[0], page_size * 2, MPOL_BIND, &node1_mask, maxnode, 0);
+	TEST_ASSERT(!ret, "mbind page 0, 1 to node 1 should succeed");
+	ret = syscall(__NR_mbind, pages[2], page_size * 2, MPOL_BIND, &node0_mask, maxnode, 0);
+	TEST_ASSERT(!ret, "mbind page 2, 3 to node 0 should succeed");
+	memset(mem, 0xaa, total_size);
+
+	/* Validate if pages are allocated on specified NUMA nodes */
+	ret = syscall(__NR_move_pages, 0, 4, pages, NULL, status, 0);
+	TEST_ASSERT(ret >= 0, "move_pages should succeed for status check");
+	TEST_ASSERT(status[0] == 1, "Page 0 should be allocated on node 1");
+	TEST_ASSERT(status[1] == 1, "Page 1 should be allocated on node 1");
+	TEST_ASSERT(status[2] == 0, "Page 2 should be allocated on node 0");
+	TEST_ASSERT(status[3] == 0, "Page 3 should be allocated on node 0");
+
+	/* Punch hole for all pages */
+	ret = fallocate(fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, total_size);
+	TEST_ASSERT(!ret, "fallocate(PUNCH_HOLE) should succeed");
+
+	/* Change NUMA policy nodes and reallocate */
+	ret = syscall(__NR_mbind, pages[0], page_size * 2, MPOL_BIND, &node0_mask, maxnode, 0);
+	TEST_ASSERT(!ret, "mbind page 0, 1 to node 0 should succeed");
+	ret = syscall(__NR_mbind, pages[2], page_size * 2, MPOL_BIND, &node1_mask, maxnode, 0);
+	TEST_ASSERT(!ret, "mbind page 2, 3 to node 1 should succeed");
+	memset(mem, 0xaa, total_size);
+
+	ret = syscall(__NR_move_pages, 0, 4, pages, NULL, status, 0);
+	TEST_ASSERT(ret >= 0, "move_pages should succeed after reallocation");
+	TEST_ASSERT(status[0] == 0, "Page 0 should be allocated on node 0");
+	TEST_ASSERT(status[1] == 0, "Page 1 should be allocated on node 0");
+	TEST_ASSERT(status[2] == 1, "Page 2 should be allocated on node 1");
+	TEST_ASSERT(status[3] == 1, "Page 3 should be allocated on node 1");
+
+	TEST_ASSERT(munmap(mem, total_size) == 0, "munmap should succeed");
+}
+
 static sigjmp_buf jmpbuf;
 void fault_sigbus_handler(int signum)
 {
@@ -286,6 +405,8 @@ static void test_guest_memfd(unsigned long vm_type)
 	if (flags & GUEST_MEMFD_FLAG_MMAP) {
 		test_mmap_supported(fd, page_size, total_size);
 		test_fault_overflow(fd, page_size, total_size);
+		test_mbind(fd, page_size, total_size);
+		test_numa_allocation(fd, page_size, total_size);
 	} else {
 		test_mmap_not_supported(fd, page_size, total_size);
 	}
-- 
2.43.0

Re: [PATCH RFC V10 0/7] Add NUMA mempolicy support for KVM guest-memfd

[Sean Christopherson]

On Mon, Aug 11, 2025, Shivank Garg wrote:
> This series introduces NUMA-aware memory placement support for KVM guests
> with guest_memfd memory backends. It builds upon Fuad Tabba's work (V17)
> that enabled host-mapping for guest_memfd memory [1].

Is this still actually an RFC?  If so, why?  If not, drop tag on the next version
(if one is needed/sent).

Re: [PATCH RFC V10 0/7] Add NUMA mempolicy support for KVM guest-memfd

[David Hildenbrand]

On 11.08.25 16:34, Sean Christopherson wrote:
> On Mon, Aug 11, 2025, Shivank Garg wrote:
>> This series introduces NUMA-aware memory placement support for KVM guests
>> with guest_memfd memory backends. It builds upon Fuad Tabba's work (V17)
>> that enabled host-mapping for guest_memfd memory [1].
> 
> Is this still actually an RFC?  If so, why?  If not, drop tag on the next version
> (if one is needed/sent).

There was the complaint that !RFC meant that it would be based on a 
consumable upstream branch.

I think once this series is rebase on top of kvm-next, we can finally 
drop the tag.

-- 
Cheers,

David / dhildenb

Re: [PATCH RFC V10 4/7] KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes

[David Hildenbrand]

On 11.08.25 11:06, Shivank Garg wrote:
> From: Ackerley Tng <ackerleytng@google.com>
> 
> guest_memfd's inode represents memory the guest_memfd is
> providing. guest_memfd's file represents a struct kvm's view of that
> memory.
> 
> Using a custom inode allows customization of the inode teardown
> process via callbacks. For example, ->evict_inode() allows
> customization of the truncation process on file close, and
> ->destroy_inode() and ->free_inode() allow customization of the inode
> freeing process.
> 
> Customizing the truncation process allows flexibility in management of
> guest_memfd memory and customization of the inode freeing process
> allows proper cleanup of memory metadata stored on the inode.
> 
> Memory metadata is more appropriately stored on the inode (as opposed
> to the file), since the metadata is for the memory and is not unique
> to a specific binding and struct kvm.
> 
> Co-developed-by: Fuad Tabba <tabba@google.com>
> Signed-off-by: Fuad Tabba <tabba@google.com>
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Shivank Garg <shivankg@amd.com>
> ---

[...]

>   
>   static int kvm_gmem_migrate_folio(struct address_space *mapping,
> @@ -463,11 +503,71 @@ bool __weak kvm_arch_supports_gmem_mmap(struct kvm *kvm)
>   	return true;
>   }
>   
> +static struct inode *kvm_gmem_inode_make_secure_inode(const char *name,
> +						      loff_t size, u64 flags)
> +{
> +	struct inode *inode;
> +
> +	inode = anon_inode_make_secure_inode(kvm_gmem_mnt->mnt_sb, name, NULL);
> +	if (IS_ERR(inode))
> +		return inode;
> +
> +	inode->i_private = (void *)(unsigned long)flags;
> +	inode->i_op = &kvm_gmem_iops;
> +	inode->i_mapping->a_ops = &kvm_gmem_aops;
> +	inode->i_mode |= S_IFREG;
> +	inode->i_size = size;
> +	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> +	mapping_set_inaccessible(inode->i_mapping);
> +	/* Unmovable mappings are supposed to be marked unevictable as well. */
> +	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
> +
> +	return inode;
> +}
> +
> +static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
> +						  u64 flags)
> +{
> +	static const char *name = "[kvm-gmem]";
> +	struct inode *inode;
> +	struct file *file;
> +	int err;
> +
> +	err = -ENOENT;

Maybe add a comment here when the module reference will get
dropped. And maybe we should just switch to fops_get() + fops_put?

/* __fput() will take care of fops_put(). */
if (!fops_get(&kvm_gmem_fops))
	goto err;

> +
> +	inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
> +	if (IS_ERR(inode)) {
> +		err = PTR_ERR(inode);
> +		goto err_put_module;
> +	}
> +
> +	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
> +				 &kvm_gmem_fops);
> +	if (IS_ERR(file)) {
> +		err = PTR_ERR(file);
> +		goto err_put_inode;
> +	}
> +
> +	file->f_flags |= O_LARGEFILE;
> +	file->private_data = priv;
> +
> +out:
> +	return file;
> +
> +err_put_inode:
> +	iput(inode);
> +err_put_module:
> +	module_put(kvm_gmem_fops.owner);

fops_put(&kvm_gmem_fops);

?


Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

Re: [PATCH RFC V10 4/7] KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes

[Ackerley Tng]

David Hildenbrand <david@redhat.com> writes:

> On 11.08.25 11:06, Shivank Garg wrote:
>> From: Ackerley Tng <ackerleytng@google.com>
>> 
>> [...snip...]
>>
>> +static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
>> +						  u64 flags)
>> +{
>> +	static const char *name = "[kvm-gmem]";
>> +	struct inode *inode;
>> +	struct file *file;
>> +	int err;
>> +
>> +	err = -ENOENT;
>
> Maybe add a comment here when the module reference will get
> dropped. And maybe we should just switch to fops_get() + fops_put?
>
> /* __fput() will take care of fops_put(). */
> if (!fops_get(&kvm_gmem_fops))
> 	goto err;
>

Sounds good! Please see attached patch. It's exactly what you suggested
except I renamed the goto target to err_fops_put:

>> +
>> +	inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
>> +	if (IS_ERR(inode)) {
>> +		err = PTR_ERR(inode);
>> +		goto err_put_module;
>> +	}
>> +
>> +	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
>> +				 &kvm_gmem_fops);
>> +	if (IS_ERR(file)) {
>> +		err = PTR_ERR(file);
>> +		goto err_put_inode;
>> +	}
>> +
>> +	file->f_flags |= O_LARGEFILE;
>> +	file->private_data = priv;
>> +
>> +out:
>> +	return file;
>> +
>> +err_put_inode:
>> +	iput(inode);
>> +err_put_module:
>> +	module_put(kvm_gmem_fops.owner);
>
> fops_put(&kvm_gmem_fops);
>
> ?
>
>
> Acked-by: David Hildenbrand <david@redhat.com>
>
> -- 
> Cheers,
>
> David / dhildenb

From f2bd4499bce4db69bf34be75e009579db4329b7c Mon Sep 17 00:00:00 2001
From: Ackerley Tng <ackerleytng@google.com>
Date: Sun, 13 Jul 2025 17:43:35 +0000
Subject: [PATCH] KVM: guest_memfd: Use guest mem inodes instead of anonymous
 inodes

guest_memfd's inode represents memory the guest_memfd is
providing. guest_memfd's file represents a struct kvm's view of that
memory.

Using a custom inode allows customization of the inode teardown
process via callbacks. For example, ->evict_inode() allows
customization of the truncation process on file close, and
->destroy_inode() and ->free_inode() allow customization of the inode
freeing process.

Customizing the truncation process allows flexibility in management of
guest_memfd memory and customization of the inode freeing process
allows proper cleanup of memory metadata stored on the inode.

Memory metadata is more appropriately stored on the inode (as opposed
to the file), since the metadata is for the memory and is not unique
to a specific binding and struct kvm.

Co-developed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 include/uapi/linux/magic.h |   1 +
 virt/kvm/guest_memfd.c     | 129 ++++++++++++++++++++++++++++++-------
 virt/kvm/kvm_main.c        |   7 +-
 virt/kvm/kvm_mm.h          |   9 +--
 4 files changed, 119 insertions(+), 27 deletions(-)

diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index bb575f3ab45e5..638ca21b7a909 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -103,5 +103,6 @@
 #define DEVMEM_MAGIC		0x454d444d	/* "DMEM" */
 #define SECRETMEM_MAGIC		0x5345434d	/* "SECM" */
 #define PID_FS_MAGIC		0x50494446	/* "PIDF" */
+#define GUEST_MEMFD_MAGIC	0x474d454d	/* "GMEM" */

 #endif /* __LINUX_MAGIC_H__ */
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 08a6bc7d25b60..6c66a09740550 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1,12 +1,16 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/anon_inodes.h>
 #include <linux/backing-dev.h>
 #include <linux/falloc.h>
+#include <linux/fs.h>
 #include <linux/kvm_host.h>
+#include <linux/pseudo_fs.h>
 #include <linux/pagemap.h>
-#include <linux/anon_inodes.h>

 #include "kvm_mm.h"

+static struct vfsmount *kvm_gmem_mnt;
+
 struct kvm_gmem {
 	struct kvm *kvm;
 	struct xarray bindings;
@@ -385,9 +389,45 @@ static struct file_operations kvm_gmem_fops = {
 	.fallocate	= kvm_gmem_fallocate,
 };

-void kvm_gmem_init(struct module *module)
+static int kvm_gmem_init_fs_context(struct fs_context *fc)
+{
+	if (!init_pseudo(fc, GUEST_MEMFD_MAGIC))
+		return -ENOMEM;
+
+	fc->s_iflags |= SB_I_NOEXEC;
+	fc->s_iflags |= SB_I_NODEV;
+
+	return 0;
+}
+
+static struct file_system_type kvm_gmem_fs = {
+	.name		 = "guest_memfd",
+	.init_fs_context = kvm_gmem_init_fs_context,
+	.kill_sb	 = kill_anon_super,
+};
+
+static int kvm_gmem_init_mount(void)
+{
+	kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);
+
+	if (IS_ERR(kvm_gmem_mnt))
+		return PTR_ERR(kvm_gmem_mnt);
+
+	kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;
+	return 0;
+}
+
+int kvm_gmem_init(struct module *module)
 {
 	kvm_gmem_fops.owner = module;
+
+	return kvm_gmem_init_mount();
+}
+
+void kvm_gmem_exit(void)
+{
+	kern_unmount(kvm_gmem_mnt);
+	kvm_gmem_mnt = NULL;
 }

 static int kvm_gmem_migrate_folio(struct address_space *mapping,
@@ -463,11 +503,72 @@ bool __weak kvm_arch_supports_gmem_mmap(struct kvm *kvm)
 	return true;
 }

+static struct inode *kvm_gmem_inode_make_secure_inode(const char *name,
+						      loff_t size, u64 flags)
+{
+	struct inode *inode;
+
+	inode = anon_inode_make_secure_inode(kvm_gmem_mnt->mnt_sb, name, NULL);
+	if (IS_ERR(inode))
+		return inode;
+
+	inode->i_private = (void *)(unsigned long)flags;
+	inode->i_op = &kvm_gmem_iops;
+	inode->i_mapping->a_ops = &kvm_gmem_aops;
+	inode->i_mode |= S_IFREG;
+	inode->i_size = size;
+	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
+	mapping_set_inaccessible(inode->i_mapping);
+	/* Unmovable mappings are supposed to be marked unevictable as well. */
+	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
+
+	return inode;
+}
+
+static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
+						  u64 flags)
+{
+	static const char *name = "[kvm-gmem]";
+	struct inode *inode;
+	struct file *file;
+	int err;
+
+	err = -ENOENT;
+	/* __fput() will take care of fops_put(). */
+	if (!fops_get(&kvm_gmem_fops))
+		goto err;
+
+	inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
+	if (IS_ERR(inode)) {
+		err = PTR_ERR(inode);
+		goto err_fops_put;
+	}
+
+	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
+				 &kvm_gmem_fops);
+	if (IS_ERR(file)) {
+		err = PTR_ERR(file);
+		goto err_put_inode;
+	}
+
+	file->f_flags |= O_LARGEFILE;
+	file->private_data = priv;
+
+out:
+	return file;
+
+err_put_inode:
+	iput(inode);
+err_fops_put:
+	fops_put(&kvm_gmem_fops);
+err:
+	file = ERR_PTR(err);
+	goto out;
+}
+
 static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 {
-	const char *anon_name = "[kvm-gmem]";
 	struct kvm_gmem *gmem;
-	struct inode *inode;
 	struct file *file;
 	int fd, err;

@@ -481,32 +582,16 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 		goto err_fd;
 	}

-	file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem,
-					 O_RDWR, NULL);
+	file = kvm_gmem_inode_create_getfile(gmem, size, flags);
 	if (IS_ERR(file)) {
 		err = PTR_ERR(file);
 		goto err_gmem;
 	}

-	file->f_flags |= O_LARGEFILE;
-
-	inode = file->f_inode;
-	WARN_ON(file->f_mapping != inode->i_mapping);
-
-	inode->i_private = (void *)(unsigned long)flags;
-	inode->i_op = &kvm_gmem_iops;
-	inode->i_mapping->a_ops = &kvm_gmem_aops;
-	inode->i_mode |= S_IFREG;
-	inode->i_size = size;
-	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
-	mapping_set_inaccessible(inode->i_mapping);
-	/* Unmovable mappings are supposed to be marked unevictable as well. */
-	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
-
 	kvm_get_kvm(kvm);
 	gmem->kvm = kvm;
 	xa_init(&gmem->bindings);
-	list_add(&gmem->entry, &inode->i_mapping->i_private_list);
+	list_add(&gmem->entry, &file_inode(file)->i_mapping->i_private_list);

 	fd_install(fd, file);
 	return fd;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 18f29ef935437..301d48d6e00d0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -6489,7 +6489,9 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
 	if (WARN_ON_ONCE(r))
 		goto err_vfio;

-	kvm_gmem_init(module);
+	r = kvm_gmem_init(module);
+	if (r)
+		goto err_gmem;

 	r = kvm_init_virtualization();
 	if (r)
@@ -6510,6 +6512,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
 err_register:
 	kvm_uninit_virtualization();
 err_virt:
+	kvm_gmem_exit();
+err_gmem:
 	kvm_vfio_ops_exit();
 err_vfio:
 	kvm_async_pf_deinit();
@@ -6541,6 +6545,7 @@ void kvm_exit(void)
 	for_each_possible_cpu(cpu)
 		free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
 	kmem_cache_destroy(kvm_vcpu_cache);
+	kvm_gmem_exit();
 	kvm_vfio_ops_exit();
 	kvm_async_pf_deinit();
 	kvm_irqfd_exit();
diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h
index 31defb08ccbab..9fcc5d5b7f8d0 100644
--- a/virt/kvm/kvm_mm.h
+++ b/virt/kvm/kvm_mm.h
@@ -68,17 +68,18 @@ static inline void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm,
 #endif /* HAVE_KVM_PFNCACHE */

 #ifdef CONFIG_KVM_GUEST_MEMFD
-void kvm_gmem_init(struct module *module);
+int kvm_gmem_init(struct module *module);
+void kvm_gmem_exit(void);
 int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args);
 int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
 		  unsigned int fd, loff_t offset);
 void kvm_gmem_unbind(struct kvm_memory_slot *slot);
 #else
-static inline void kvm_gmem_init(struct module *module)
+static inline int kvm_gmem_init(struct module *module)
 {
-
+	return 0;
 }
-
+static inline void kvm_gmem_exit(void) {};
 static inline int kvm_gmem_bind(struct kvm *kvm,
 					 struct kvm_memory_slot *slot,
 					 unsigned int fd, loff_t offset)
--
2.51.0.rc0.155.g4a0f42376b-goog

Re: [PATCH RFC V10 4/7] KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes

[Garg, Shivank]

On 8/12/2025 2:53 AM, Ackerley Tng wrote:
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 11.08.25 11:06, Shivank Garg wrote:
>>> From: Ackerley Tng <ackerleytng@google.com>
>>>
>>> [...snip...]
>>>
>>> +static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
>>> +						  u64 flags)
>>> +{
>>> +	static const char *name = "[kvm-gmem]";
>>> +	struct inode *inode;
>>> +	struct file *file;
>>> +	int err;
>>> +
>>> +	err = -ENOENT;
>>
>> Maybe add a comment here when the module reference will get
>> dropped. And maybe we should just switch to fops_get() + fops_put?
>>
>> /* __fput() will take care of fops_put(). */
>> if (!fops_get(&kvm_gmem_fops))
>> 	goto err;
>>
> 
> Sounds good! Please see attached patch. It's exactly what you suggested
> except I renamed the goto target to err_fops_put:
> 
>>> +
>>> +	inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
>>> +	if (IS_ERR(inode)) {
>>> +		err = PTR_ERR(inode);
>>> +		goto err_put_module;
>>> +	}
>>> +
>>> +	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
>>> +				 &kvm_gmem_fops);
>>> +	if (IS_ERR(file)) {
>>> +		err = PTR_ERR(file);
>>> +		goto err_put_inode;
>>> +	}
>>> +
>>> +	file->f_flags |= O_LARGEFILE;
>>> +	file->private_data = priv;
>>> +
>>> +out:
>>> +	return file;
>>> +
>>> +err_put_inode:
>>> +	iput(inode);
>>> +err_put_module:
>>> +	module_put(kvm_gmem_fops.owner);
>>
>> fops_put(&kvm_gmem_fops);
>>
>> ?
>>
>>
>> Acked-by: David Hildenbrand <david@redhat.com>
>>
>> -- 
>> Cheers,
>>
>> David / dhildenb
> 
> From f2bd4499bce4db69bf34be75e009579db4329b7c Mon Sep 17 00:00:00 2001
> From: Ackerley Tng <ackerleytng@google.com>
> Date: Sun, 13 Jul 2025 17:43:35 +0000
> Subject: [PATCH] KVM: guest_memfd: Use guest mem inodes instead of anonymous
>  inodes
> 
> guest_memfd's inode represents memory the guest_memfd is
> providing. guest_memfd's file represents a struct kvm's view of that
> memory.
> 
> Using a custom inode allows customization of the inode teardown
> process via callbacks. For example, ->evict_inode() allows
> customization of the truncation process on file close, and
> ->destroy_inode() and ->free_inode() allow customization of the inode
> freeing process.
> 
> Customizing the truncation process allows flexibility in management of
> guest_memfd memory and customization of the inode freeing process
> allows proper cleanup of memory metadata stored on the inode.
> 
> Memory metadata is more appropriately stored on the inode (as opposed
> to the file), since the metadata is for the memory and is not unique
> to a specific binding and struct kvm.
> 
> Co-developed-by: Fuad Tabba <tabba@google.com>
> Signed-off-by: Fuad Tabba <tabba@google.com>
> Signed-off-by: Shivank Garg <shivankg@amd.com>
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> ---
>  include/uapi/linux/magic.h |   1 +
>  virt/kvm/guest_memfd.c     | 129 ++++++++++++++++++++++++++++++-------
>  virt/kvm/kvm_main.c        |   7 +-
>  virt/kvm/kvm_mm.h          |   9 +--
>  4 files changed, 119 insertions(+), 27 deletions(-)
> 
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index bb575f3ab45e5..638ca21b7a909 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -103,5 +103,6 @@
>  #define DEVMEM_MAGIC		0x454d444d	/* "DMEM" */
>  #define SECRETMEM_MAGIC		0x5345434d	/* "SECM" */
>  #define PID_FS_MAGIC		0x50494446	/* "PIDF" */
> +#define GUEST_MEMFD_MAGIC	0x474d454d	/* "GMEM" */
> 
>  #endif /* __LINUX_MAGIC_H__ */
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 08a6bc7d25b60..6c66a09740550 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -1,12 +1,16 @@
>  // SPDX-License-Identifier: GPL-2.0
> +#include <linux/anon_inodes.h>
>  #include <linux/backing-dev.h>
>  #include <linux/falloc.h>
> +#include <linux/fs.h>
>  #include <linux/kvm_host.h>
> +#include <linux/pseudo_fs.h>
>  #include <linux/pagemap.h>
> -#include <linux/anon_inodes.h>
> 
>  #include "kvm_mm.h"
> 
> +static struct vfsmount *kvm_gmem_mnt;
> +
>  struct kvm_gmem {
>  	struct kvm *kvm;
>  	struct xarray bindings;
> @@ -385,9 +389,45 @@ static struct file_operations kvm_gmem_fops = {
>  	.fallocate	= kvm_gmem_fallocate,
>  };
> 
> -void kvm_gmem_init(struct module *module)
> +static int kvm_gmem_init_fs_context(struct fs_context *fc)
> +{
> +	if (!init_pseudo(fc, GUEST_MEMFD_MAGIC))
> +		return -ENOMEM;
> +
> +	fc->s_iflags |= SB_I_NOEXEC;
> +	fc->s_iflags |= SB_I_NODEV;
> +
> +	return 0;
> +}
> +
> +static struct file_system_type kvm_gmem_fs = {
> +	.name		 = "guest_memfd",
> +	.init_fs_context = kvm_gmem_init_fs_context,
> +	.kill_sb	 = kill_anon_super,
> +};
> +
> +static int kvm_gmem_init_mount(void)
> +{
> +	kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);
> +
> +	if (IS_ERR(kvm_gmem_mnt))
> +		return PTR_ERR(kvm_gmem_mnt);
> +
> +	kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;
> +	return 0;
> +}
> +
> +int kvm_gmem_init(struct module *module)
>  {
>  	kvm_gmem_fops.owner = module;
> +
> +	return kvm_gmem_init_mount();
> +}
> +
> +void kvm_gmem_exit(void)
> +{
> +	kern_unmount(kvm_gmem_mnt);
> +	kvm_gmem_mnt = NULL;
>  }
> 
>  static int kvm_gmem_migrate_folio(struct address_space *mapping,
> @@ -463,11 +503,72 @@ bool __weak kvm_arch_supports_gmem_mmap(struct kvm *kvm)
>  	return true;
>  }
> 
> +static struct inode *kvm_gmem_inode_make_secure_inode(const char *name,
> +						      loff_t size, u64 flags)
> +{
> +	struct inode *inode;
> +
> +	inode = anon_inode_make_secure_inode(kvm_gmem_mnt->mnt_sb, name, NULL);
> +	if (IS_ERR(inode))
> +		return inode;
> +
> +	inode->i_private = (void *)(unsigned long)flags;
> +	inode->i_op = &kvm_gmem_iops;
> +	inode->i_mapping->a_ops = &kvm_gmem_aops;
> +	inode->i_mode |= S_IFREG;
> +	inode->i_size = size;
> +	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> +	mapping_set_inaccessible(inode->i_mapping);
> +	/* Unmovable mappings are supposed to be marked unevictable as well. */
> +	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
> +
> +	return inode;
> +}
> +
> +static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
> +						  u64 flags)
> +{
> +	static const char *name = "[kvm-gmem]";
> +	struct inode *inode;
> +	struct file *file;
> +	int err;
> +
> +	err = -ENOENT;
> +	/* __fput() will take care of fops_put(). */
> +	if (!fops_get(&kvm_gmem_fops))
> +		goto err;
> +
> +	inode = kvm_gmem_inode_make_secure_inode(name, size, flags);
> +	if (IS_ERR(inode)) {
> +		err = PTR_ERR(inode);
> +		goto err_fops_put;
> +	}
> +
> +	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR,
> +				 &kvm_gmem_fops);
> +	if (IS_ERR(file)) {
> +		err = PTR_ERR(file);
> +		goto err_put_inode;
> +	}
> +
> +	file->f_flags |= O_LARGEFILE;
> +	file->private_data = priv;
> +
> +out:
> +	return file;
> +
> +err_put_inode:
> +	iput(inode);
> +err_fops_put:
> +	fops_put(&kvm_gmem_fops);

Thanks Ackerley.
LGTM

Re: [PATCH RFC V10 5/7] KVM: guest_memfd: Add slab-allocated inode cache

[Garg, Shivank]

On 8/11/2025 2:36 PM, Shivank Garg wrote:
> Add dedicated inode structure (kvm_gmem_inode_info) and slab-allocated
> inode cache for guest memory backing, similar to how shmem handles inodes.
> 
> This adds the necessary allocation/destruction functions and prepares
> for upcoming guest_memfd NUMA policy support changes.
> 
> Signed-off-by: Shivank Garg <shivankg@amd.com>
> ---
>  virt/kvm/guest_memfd.c | 69 ++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 67 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 0e93323fc839..d9c23401e770 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -17,6 +17,15 @@ struct kvm_gmem {
>  	struct list_head entry;
>  };
>  
> +struct kvm_gmem_inode_info {
> +	struct inode vfs_inode;
> +};
> +
> +static inline struct kvm_gmem_inode_info *KVM_GMEM_I(struct inode *inode)
> +{
> +	return container_of(inode, struct kvm_gmem_inode_info, vfs_inode);
> +}
> +
>  /**
>   * folio_file_pfn - like folio_file_page, but return a pfn.
>   * @folio: The folio which contains this index.
> @@ -389,13 +398,46 @@ static struct file_operations kvm_gmem_fops = {
>  	.fallocate	= kvm_gmem_fallocate,
>  };
>  
> +static struct kmem_cache *kvm_gmem_inode_cachep;
> +
> +static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
> +{
> +	struct kvm_gmem_inode_info *info;
> +
> +	info = alloc_inode_sb(sb, kvm_gmem_inode_cachep, GFP_KERNEL);
> +	if (!info)
> +		return NULL;
> +
> +	return &info->vfs_inode;
> +}
> +
> +static void kvm_gmem_destroy_inode(struct inode *inode)
> +{
> +}
> +
> +static void kvm_gmem_free_inode(struct inode *inode)
> +{
> +	kmem_cache_free(kvm_gmem_inode_cachep, KVM_GMEM_I(inode));
> +}
> +
> +static const struct super_operations kvm_gmem_super_operations = {
> +	.statfs		= simple_statfs,
> +	.alloc_inode	= kvm_gmem_alloc_inode,
> +	.destroy_inode	= kvm_gmem_destroy_inode,
> +	.free_inode	= kvm_gmem_free_inode,
> +};
> +
>  static int kvm_gmem_init_fs_context(struct fs_context *fc)
>  {
> +	struct pseudo_fs_context *ctx;
> +
>  	if (!init_pseudo(fc, GUEST_MEMFD_MAGIC))
>  		return -ENOMEM;
>  
>  	fc->s_iflags |= SB_I_NOEXEC;
>  	fc->s_iflags |= SB_I_NODEV;
> +	ctx = fc->fs_private;
> +	ctx->ops = &kvm_gmem_super_operations;
>  
>  	return 0;
>  }
> @@ -417,17 +459,40 @@ static int kvm_gmem_init_mount(void)
>  	return 0;
>  }
>  
> +static void kvm_gmem_init_inode(void *foo)
> +{
> +	struct kvm_gmem_inode_info *info = foo;
> +
> +	inode_init_once(&info->vfs_inode);
> +}
> +
>  int kvm_gmem_init(struct module *module)
>  {
> -	kvm_gmem_fops.owner = module;
> +	int ret;
> +	struct kmem_cache_args args = {
> +		.align = 0,
> +		.ctor = kvm_gmem_init_inode,
> +	};
>  
> -	return kvm_gmem_init_mount();
> +	kvm_gmem_fops.owner = module;
> +	kvm_gmem_inode_cachep = kmem_cache_create("kvm_gmem_inode_cache",
> +						  sizeof(struct kvm_gmem_inode_info),
> +						  &args, SLAB_ACCOUNT);
> +	if (!kvm_gmem_inode_cachep)
> +		return -ENOMEM;
> +	ret = kvm_gmem_init_mount();
> +	if (ret) {
> +		kmem_cache_destroy(kvm_gmem_inode_cachep);
> +		return ret;
> +	}
> +	return 0;
>  }
>  
>  void kvm_gmem_exit(void)
>  {
>  	kern_unmount(kvm_gmem_mnt);
>  	kvm_gmem_mnt = NULL;
> +	kmem_cache_destroy(kvm_gmem_inode_cachep);
>  }

While testing my code, I discovered a bug that occurs when unloading the kvm_amd module
after a guest_memfd-backed VM has run.

dmesg logs:
[  610.075763] =============================================================================
[  610.083933] BUG kvm_gmem_inode_cache (Not tainted): Objects remaining on __kmem_cache_shutdown()
[  610.092711] -----------------------------------------------------------------------------
[  610.102368] Object 0x000000008ee52a58 @offset=19200
[  610.107247] Slab 0x000000004b1b088c objects=51 used=1 fp=0x000000007c55fc00 flags=0x57ffffc0000240(workingset|head|node=1|zone=2|lastcpupid=0x1fffff)
[  610.120733] Disabling lock debugging due to kernel taint
[  610.120741] ------------[ cut here ]------------
[  610.120742] WARNING: CPU: 7 PID: 7554 at mm/slub.c:1171 __kmem_cache_shutdown+0x264/0x370
[  610.120751] Modules linked in: xt_set ip_set xt_addrtype xfrm_user xfrm_algo xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_reject_ipv4 nft_compat nff_defrag_ipv4 nf_tables overlay bridge stp llc cfg80211 rfkill binfmt_misc ipmi_ssif amd_atl intel_rapl_msr wmi_bmof intel_rapl_common amd64_edac edac_mce_amdmem_helper drm_kms_helper i2c_piix4 ptdma i2c_smbus k10temp wmi acpi_power_meter ipmi_si acpi_ipmi ipmi_devintf ipmi_msghandler sg dm_multipath fuse drm dm_mo56 async_raid6_recov async_memcpy async_pq async_xor xor async_tx raid6_pq raid1 raid0 sd_mod kvm_amd(-) ahci libahci kvm nvme tg3 libata ccp irqbypass nvme_c
[  610.120831] CPU: 7 UID: 0 PID: 7554 Comm: rmmod Kdump: loaded Tainted: G    B               6.16.0+ #10 PREEMPT(none)
[  610.120835] Tainted: [B]=BAD_PAGE
[  610.120836] Hardware name: Dell Inc. PowerEdge R6525/024PW1, BIOS 2.16.2 07/09/2024
[  610.120838] RIP: 0010:__kmem_cache_shutdown+0x264/0x370
[  610.120841] Code: 89 f1 4c 89 f6 4d 8b 46 20 48 c7 c7 08 08 ec 87 81 e2 ff 7f 00 00 e8 fb a7 d7 ff be 01 00 00 00 bf 05 00 00 00 e8 dc e9 cd ff <0f> 0b 48 fe ff ff
[  610.120843] RSP: 0018:ffffcd6962963cb8 EFLAGS: 00010046
[  610.120846] RAX: 0000000000000000 RBX: ffff89fde07d21c0 RCX: 0000000000000027
[  610.120848] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff89fcbe5dbe80
[  610.120850] RBP: ffff89fde07d21c0 R08: 0000000000000000 R09: 0000000000000003
[  610.120851] R10: ffffcd6962963b58 R11: ffffffff889db908 R12: ffff89fdcccd7f80
[  610.120852] R13: ffff89fdcccd0000 R14: fffff96802333400 R15: ffff89fdd6ab6c00
[  610.120854] FS:  00007f066eaab080(0000) GS:ffff89fd3516f000(0000) knlGS:0000000000000000
[  610.120856] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  610.120857] CR2: 00007ffefd577828 CR3: 0000000220406004 CR4: 0000000000770ef0
[  610.120859] PKRU: 55555554
[  610.120860] Call Trace:
[  610.120862]  <TASK>
[  610.120866]  kmem_cache_destroy+0x3a/0x150
[  610.120872]  kvm_exit+0x7b/0xa0 [kvm]
[  610.120919]  svm_exit+0x5/0x10 [kvm_amd]
[  610.120926]  __do_sys_delete_module.isra.0+0x18b/0x2e0
[  610.120933]  ? srso_alias_return_thunk+0x5/0xfbef5
[  610.120937]  ? syscall_trace_enter+0xfa/0x1a0
[  610.120941]  do_syscall_64+0x7b/0x2c0
[  610.120947]  ? srso_alias_return_thunk+0x5/0xfbef5
[  610.120950]  ? __handle_mm_fault+0x2aa/0x670
[  610.120954]  ? iterate_dir+0x11e/0x230
[  610.120960]  ? srso_alias_return_thunk+0x5/0xfbef5
[  610.120963]  ? count_memcg_events+0xb2/0x160
[  610.120967]  ? srso_alias_return_thunk+0x5/0xfbef5
[  610.120969]  ? handle_mm_fault+0xb2/0x2f0
[  610.120972]  ? srso_alias_return_thunk+0x5/0xfbef5
[  610.120975]  ? do_user_addr_fault+0x16f/0x6f0
[  610.120981]  ? srso_alias_return_thunk+0x5/0xfbef5
[  610.120984]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  610.120986] RIP: 0033:0x7f066e12ac9b
[  610.120989] Code: 73 01 c3 48 8b 0d 7d 81 0d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00 00 0f 05 <48> 3d 01 89 01 48
[  610.120990] RSP: 002b:00007ffc629f1878 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
[  610.120993] RAX: ffffffffffffffda RBX: 00005630e80256f0 RCX: 00007f066e12ac9b
[  610.120994] RDX: 0000000000000000 RSI: 0000000000000800 RDI: 00005630e8025758
[  610.120996] RBP: 00007ffc629f18a0 R08: 1999999999999999 R09: 0000000000000000
[  610.120997] R10: 00007f066e1b1fc0 R11: 0000000000000206 R12: 0000000000000000
[  610.120999] R13: 00007ffc629f1af0 R14: 00005630e80256f0 R15: 0000000000000000
[  610.121003]  </TASK>
[  610.121004] ---[ end trace 0000000000000000 ]---
[  610.121017] ------------[ cut here ]------------

There is a race condition here:
kern_unmount() -> mntput() -> cleanup_mnt() -> deactivate_super() -> deactivate_locked_super() -> fs->kill_sb() (guest_memfd kill_sb) -> generic_shutdown_super() -> evict_inodes() -> destroy_inode() -> call_rcu()

I should be waiting for pending RCU callback to finish before calling the kmem_cache_destroy().

To fix this, I added rcu_barrier() like dax_fs_exit() is doing.

@@ -561,6 +566,7 @@ void kvm_gmem_exit(void)
 {
        kern_unmount(kvm_gmem_mnt);
        kvm_gmem_mnt = NULL;
+       rcu_barrier();
        kmem_cache_destroy(kvm_gmem_inode_cachep);
 }


I'll incorporate this fix into next version.

Thanks,
Shivank