* + mm-add-vm_uffd_rwp-vma-flag.patch added to mm-new branch
@ 2026-07-09 2:06 Andrew Morton
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From: Andrew Morton @ 2026-07-09 2:06 UTC (permalink / raw)
To: mm-commits, kas, akpm
The patch titled
Subject: mm: add VM_UFFD_RWP VMA flag
has been added to the -mm mm-new branch. Its filename is
mm-add-vm_uffd_rwp-vma-flag.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-add-vm_uffd_rwp-vma-flag.patch
This patch will later appear in the mm-new branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews. Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.
The mm-new branch of mm.git is not included in linux-next
If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
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------------------------------------------------------
From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
Subject: mm: add VM_UFFD_RWP VMA flag
Date: Wed, 8 Jul 2026 12:14:06 +0100
Preparatory patch for userfaultfd read-write protection (RWP). RWP
extends userfaultfd protection from plain write-protection (WP) to full
read-write protection: accesses to an RWP-protected range -- reads as well
as writes -- trap through userfaultfd.
Reserve VM_UFFD_RWP, add the userfaultfd_rwp() and userfaultfd_protected()
helpers, and wire up the smaps "ur" entry and the trace-flag table the
rest of the series will use. The flag is gated on CONFIG_USERFAULTFD_RWP,
which is introduced together with the UAPI in a later patch; until then
VM_UFFD_RWP aliases VM_NONE and every downstream check folds to dead code.
Nothing sets or queries the flag yet.
Link: https://lore.kernel.org/20260708111417.173443-6-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: James Houghton <jthoughton@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
Documentation/filesystems/proc.rst | 1
fs/proc/task_mmu.c | 3 +
include/linux/mm.h | 41 ++++++++++++++++--------
include/linux/userfaultfd_k.h | 45 +++++++++++++++++++++------
include/trace/events/mmflags.h | 7 ++++
5 files changed, 74 insertions(+), 23 deletions(-)
--- a/Documentation/filesystems/proc.rst~mm-add-vm_uffd_rwp-vma-flag
+++ a/Documentation/filesystems/proc.rst
@@ -608,6 +608,7 @@ encoded manner. The codes are the follow
um userfaultfd missing tracking
uw userfaultfd wr-protect tracking
ui userfaultfd minor fault
+ ur userfaultfd read-write-protect tracking
ss shadow/guarded control stack page
sl sealed
lf lock on fault pages
--- a/fs/proc/task_mmu.c~mm-add-vm_uffd_rwp-vma-flag
+++ a/fs/proc/task_mmu.c
@@ -1237,6 +1237,9 @@ static void show_smap_vma_flags(struct s
#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
[ilog2(VM_UFFD_MINOR)] = "ui",
#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
+#ifdef CONFIG_USERFAULTFD_RWP
+ [ilog2(VM_UFFD_RWP)] = "ur",
+#endif
#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
[ilog2(VM_SHADOW_STACK)] = "ss",
#endif
--- a/include/linux/mm.h~mm-add-vm_uffd_rwp-vma-flag
+++ a/include/linux/mm.h
@@ -354,6 +354,7 @@ enum {
#endif
DECLARE_VMA_BIT(UFFD_MINOR, 41),
DECLARE_VMA_BIT(SEALED, 42),
+ DECLARE_VMA_BIT(UFFD_RWP, 43),
/* Flags that reuse flags above. */
DECLARE_VMA_BIT_ALIAS(PKEY_BIT0, HIGH_ARCH_0),
DECLARE_VMA_BIT_ALIAS(PKEY_BIT1, HIGH_ARCH_1),
@@ -497,12 +498,17 @@ enum {
#else
#define VM_UFFD_MINOR VM_NONE
#endif
+#ifdef CONFIG_USERFAULTFD_RWP
+#define VM_UFFD_RWP INIT_VM_FLAG(UFFD_RWP)
+#else
+#define VM_UFFD_RWP VM_NONE
+#endif
/*
- * vma_flags_t masks for the userfaultfd VMA flags. VMA_UFFD_MINOR is gated on
- * the same config as VM_UFFD_MINOR -- which implies 64BIT, where the bit fits
- * -- so an out-of-range bit is never fed to mk_vma_flags() on a build whose
- * bitmap cannot hold it.
+ * vma_flags_t masks for the userfaultfd VMA flags. The two high-bit modes are
+ * gated on the same configs as their VM_* flags above -- both of which imply
+ * 64BIT -- so an out-of-range bit is never fed to mk_vma_flags() on a build
+ * whose bitmap cannot hold it.
*/
#define VMA_UFFD_MISSING mk_vma_flags(VMA_UFFD_MISSING_BIT)
#define VMA_UFFD_WP mk_vma_flags(VMA_UFFD_WP_BIT)
@@ -511,6 +517,11 @@ enum {
#else
#define VMA_UFFD_MINOR EMPTY_VMA_FLAGS
#endif
+#ifdef CONFIG_USERFAULTFD_RWP
+#define VMA_UFFD_RWP mk_vma_flags(VMA_UFFD_RWP_BIT)
+#else
+#define VMA_UFFD_RWP EMPTY_VMA_FLAGS
+#endif
#ifdef CONFIG_64BIT
#define VM_ALLOW_ANY_UNCACHED INIT_VM_FLAG(ALLOW_ANY_UNCACHED)
@@ -649,22 +660,24 @@ enum {
* reconsistuted upon page fault, so necessitate page table copying upon fork.
*
* Note that these flags should be compared with the DESTINATION VMA not the
- * source, as VM_UFFD_WP may not be propagated to destination, while all other
- * flags will be.
+ * source: VM_UFFD_WP and VM_UFFD_RWP may be cleared on the destination
+ * (dup_userfaultfd() -> userfaultfd_reset_ctx() when the parent context did
+ * not negotiate UFFD_FEATURE_EVENT_FORK), while all other flags propagate.
*
* VM_PFNMAP / VM_MIXEDMAP - These contain kernel-mapped data which cannot be
* reasonably reconstructed on page fault.
*
* VM_UFFD_WP - Encodes metadata about an installed uffd
- * write protect handler, which cannot be
- * reconstructed on page fault.
+ * VM_UFFD_RWP write- or read-write-protect handler, which
+ * cannot be reconstructed on page fault.
*
- * We always copy pgtables when dst_vma has uffd-wp
- * enabled even if it's file-backed
- * (e.g. shmem). Because when uffd-wp is enabled,
- * pgtable contains uffd-wp protection information,
- * that's something we can't retrieve from page cache,
- * and skip copying will lose those info.
+ * We always copy pgtables when dst_vma has the
+ * uffd PTE bit in use even if it's file-backed
+ * (e.g. shmem). Because when the uffd bit is
+ * in use, the pgtable contains the protection
+ * information, that's something we can't
+ * retrieve from page cache, and skip copying
+ * will lose those info.
*
* VM_MAYBE_GUARD - Could contain page guard region markers which
* by design are a property of the page tables
--- a/include/linux/userfaultfd_k.h~mm-add-vm_uffd_rwp-vma-flag
+++ a/include/linux/userfaultfd_k.h
@@ -21,10 +21,11 @@
#include <linux/hugetlb_inline.h>
/* The set of all possible UFFD-related VM flags. */
-#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_WP | VM_UFFD_MINOR)
+#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_MINOR | \
+ VM_UFFD_WP | VM_UFFD_RWP)
#define __VMA_UFFD_FLAGS mk_vma_flags_from_masks(VMA_UFFD_MISSING, VMA_UFFD_WP, \
- VMA_UFFD_MINOR)
+ VMA_UFFD_MINOR, VMA_UFFD_RWP)
/*
* CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
@@ -168,7 +169,8 @@ static inline bool is_mergeable_vm_userf
/*
* Never enable huge pmd sharing on some uffd registered vmas:
*
- * - VM_UFFD_WP VMAs, because write protect information is per pgtable entry.
+ * - VM_UFFD_WP and VM_UFFD_RWP VMAs, because the write protect / access
+ * tracking information is per pgtable entry.
*
* - VM_UFFD_MINOR VMAs, because otherwise we would never get minor faults for
* VMAs which share huge pmds. (If you have two mappings to the same
@@ -179,20 +181,25 @@ static inline bool is_mergeable_vm_userf
static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma)
{
return vma_test_any_mask(vma,
- mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_MINOR));
+ mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP,
+ VMA_UFFD_MINOR));
}
/*
- * Don't do fault around for either WP or MINOR registered uffd range. For
+ * Don't do fault around for WP, RWP or MINOR registered uffd range. For
* MINOR registered range, fault around will be a total disaster and ptes can
* be installed without notifications; for WP it should mostly be fine as long
* as the fault around checks for pte_none() before the installation, however
- * to be super safe we just forbid it.
+ * to be super safe we just forbid it; for RWP, pre-faulted neighbours would
+ * be indistinguishable from accessed pages in PAGEMAP_SCAN (PAGE_IS_ACCESSED)
+ * and pollute the tracked working set, so each page must be populated by its
+ * own fault.
*/
static inline bool uffd_disable_fault_around(struct vm_area_struct *vma)
{
return vma_test_any_mask(vma,
- mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_MINOR));
+ mk_vma_flags_from_masks(VMA_UFFD_WP, VMA_UFFD_RWP,
+ VMA_UFFD_MINOR));
}
static inline bool userfaultfd_missing(struct vm_area_struct *vma)
@@ -210,6 +217,16 @@ static inline bool userfaultfd_minor(str
return vma_test_any_mask(vma, VMA_UFFD_MINOR);
}
+static inline bool userfaultfd_rwp(struct vm_area_struct *vma)
+{
+ return vma_test_single_mask(vma, VMA_UFFD_RWP);
+}
+
+static inline bool userfaultfd_protected(struct vm_area_struct *vma)
+{
+ return userfaultfd_wp(vma) || userfaultfd_rwp(vma);
+}
+
static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma,
pte_t pte)
{
@@ -330,6 +347,16 @@ static inline bool userfaultfd_minor(str
return false;
}
+static inline bool userfaultfd_rwp(struct vm_area_struct *vma)
+{
+ return false;
+}
+
+static inline bool userfaultfd_protected(struct vm_area_struct *vma)
+{
+ return false;
+}
+
static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma,
pte_t pte)
{
@@ -423,8 +450,8 @@ static inline bool userfaultfd_wp_use_ma
}
/*
- * Returns true if this is a swap pte and was uffd-wp wr-protected in either
- * forms (pte marker or a normal swap pte), false otherwise.
+ * Returns true if this swap pte carries uffd-tracked state in either
+ * form (pte marker or a normal swap pte), false otherwise.
*/
static inline bool pte_swp_uffd_any(pte_t pte)
{
--- a/include/trace/events/mmflags.h~mm-add-vm_uffd_rwp-vma-flag
+++ a/include/trace/events/mmflags.h
@@ -186,6 +186,12 @@ IF_HAVE_PG_ARCH_3(arch_3)
# define IF_HAVE_UFFD_MINOR(flag, name)
#endif
+#ifdef CONFIG_USERFAULTFD_RWP
+# define IF_HAVE_UFFD_RWP(flag, name) {flag, name},
+#else
+# define IF_HAVE_UFFD_RWP(flag, name)
+#endif
+
#if defined(CONFIG_64BIT) || defined(CONFIG_PPC32)
# define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
#else
@@ -207,6 +213,7 @@ IF_HAVE_UFFD_MINOR(VM_UFFD_MINOR, "uffd_
{VM_PFNMAP, "pfnmap" }, \
{VM_MAYBE_GUARD, "maybe_guard" }, \
{VM_UFFD_WP, "uffd_wp" }, \
+IF_HAVE_UFFD_RWP(VM_UFFD_RWP, "uffd_rwp" ) \
{VM_LOCKED, "locked" }, \
{VM_IO, "io" }, \
{VM_SEQ_READ, "seqread" }, \
_
Patches currently in -mm which might be from kas@kernel.org are
mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork.patch
fs-proc-task_mmu-fix-pagemap_scan-written-state-for-unpopulated-ptes.patch
mm-decouple-protnone-helpers-from-config_numa_balancing.patch
mm-rename-uffd-wp-pte-bit-macros-to-uffd.patch
mm-rename-uffd-wp-pte-accessors-to-uffd.patch
userfaultfd-test-uffd-vma-flags-through-the-vma_flags_t-api.patch
mm-add-vm_uffd_rwp-vma-flag.patch
mm-add-mm_cp_uffd_rwp-change_protection-flag.patch
mm-preserve-rwp-marker-across-pte-rewrites.patch
mm-handle-vm_uffd_rwp-in-khugepaged-rmap-and-gup.patch
userfaultfd-add-uffdio_register_mode_rwp-and-uffdio_rwprotect-plumbing.patch
mm-userfaultfd-add-rwp-fault-delivery-and-expose-uffdio_register_mode_rwp.patch
mm-pagemap-add-page_is_accessed-for-rwp-tracking.patch
userfaultfd-add-uffd_feature_rwp_async-for-async-fault-resolution.patch
userfaultfd-add-uffdio_set_mode-for-runtime-sync-async-toggle.patch
selftests-mm-add-userfaultfd-rwp-tests.patch
documentation-userfaultfd-document-rwp-working-set-tracking.patch
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