Patch "mm: add atomic VMA flags and set VM_MAYBE_GUARD as such" has been added to the 6.18-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mm: add atomic VMA flags and set VM_MAYBE_GUARD as such

to the 6.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-add-atomic-vma-flags-and-set-vm_maybe_guard-as-such.patch
and it can be found in the queue-6.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-247749-greg=kroah.com@vger.kernel.org Fri May 15 14:05:33 2026
From: Ahmed Elaidy <elaidya225@gmail.com>
Date: Fri, 15 May 2026 15:42:12 +0300
Subject: mm: add atomic VMA flags and set VM_MAYBE_GUARD as such
To: stable@vger.kernel.org
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, ljs@kernel.org, avagin@gmail.com, Lorenzo Stoakes <lorenzo.stoakes@oracle.com>, Pedro Falcato <pfalcato@suse.de>, Vlastimil Babka <vbabka@suse.cz>, "David Hildenbrand (Red Hat)" <david@kernel.org>, Lance Yang <lance.yang@linux.dev>, Baolin Wang <baolin.wang@linux.alibaba.com>, Barry Song <baohua@kernel.org>, Dev Jain <dev.jain@arm.com>, Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>, Liam Howlett <liam.howlett@oracle.com>, "Masami Hiramatsu (Google)" <mhiramat@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Michal Hocko <mhocko@suse.com>, Mike Rapoport <rppt@kernel.org>, Nico Pache <npache@redhat.com>, Ryan Roberts <ryan.roberts@arm.com>, Steven Rostedt <rostedt@goodmis.org>, Suren Baghdasaryan <surenb@google.com>, Zi Yan <ziy@nvidia.com>, Ahmed Elaidy <elaidya225@gmail.com>
Message-ID: <20260515124218.151966-4-elaidya225@gmail.com>

From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

commit 568822502383acd57d7cc1c72ee43932c45a9524 upstream.

This patch adds the ability to atomically set VMA flags with only the mmap
read/VMA read lock held.

As this could be hugely problematic for VMA flags in general given that
all other accesses are non-atomic and serialised by the mmap/VMA locks, we
implement this with a strict allow-list - that is, only designated flags
are allowed to do this.

We make VM_MAYBE_GUARD one of these flags.

Link: https://lkml.kernel.org/r/97e57abed09f2663077ed7a36fb8206e243171a9.1763460113.git.ljs@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ahmed Elaidy <elaidya225@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/mm.h |   44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -501,6 +501,9 @@ extern unsigned int kobjsize(const void
 /* This mask represents all the VMA flag bits used by mlock */
 #define VM_LOCKED_MASK	(VM_LOCKED | VM_LOCKONFAULT)
 
+/* These flags can be updated atomically via VMA/mmap read lock. */
+#define VM_ATOMIC_SET_ALLOWED VM_MAYBE_GUARD
+
 /* Arch-specific flags to clear when updating VM flags on protection change */
 #ifndef VM_ARCH_CLEAR
 # define VM_ARCH_CLEAR	VM_NONE
@@ -843,6 +846,47 @@ static inline void vm_flags_mod(struct v
 	__vm_flags_mod(vma, set, clear);
 }
 
+static inline bool __vma_flag_atomic_valid(struct vm_area_struct *vma,
+				       int bit)
+{
+	const vm_flags_t mask = BIT(bit);
+
+	/* Only specific flags are permitted */
+	if (WARN_ON_ONCE(!(mask & VM_ATOMIC_SET_ALLOWED)))
+		return false;
+
+	return true;
+}
+
+/*
+ * Set VMA flag atomically. Requires only VMA/mmap read lock. Only specific
+ * valid flags are allowed to do this.
+ */
+static inline void vma_flag_set_atomic(struct vm_area_struct *vma, int bit)
+{
+	/* mmap read lock/VMA read lock must be held. */
+	if (!rwsem_is_locked(&vma->vm_mm->mmap_lock))
+		vma_assert_locked(vma);
+
+	if (__vma_flag_atomic_valid(vma, bit))
+		set_bit(bit, &ACCESS_PRIVATE(vma, __vm_flags));
+}
+
+/*
+ * Test for VMA flag atomically. Requires no locks. Only specific valid flags
+ * are allowed to do this.
+ *
+ * This is necessarily racey, so callers must ensure that serialisation is
+ * achieved through some other means, or that races are permissible.
+ */
+static inline bool vma_flag_test_atomic(struct vm_area_struct *vma, int bit)
+{
+	if (__vma_flag_atomic_valid(vma, bit))
+		return test_bit(bit, &vma->vm_flags);
+
+	return false;
+}
+
 static inline void vma_set_anonymous(struct vm_area_struct *vma)
 {
 	vma->vm_ops = NULL;


Patches currently in stable-queue which might be from elaidya225@gmail.com are

queue-6.18/testing-selftests-mm-add-soft-dirty-merge-self-test.patch
queue-6.18/mm-implement-sticky-vma-flags.patch
queue-6.18/mm-update-vma_modify_flags-to-handle-residual-flags-document.patch
queue-6.18/mm-add-atomic-vma-flags-and-set-vm_maybe_guard-as-such.patch
queue-6.18/mm-propagate-vm_softdirty-on-merge.patch
queue-6.18/mm-set-the-vm_maybe_guard-flag-on-guard-region-install.patch
queue-6.18/mm-introduce-copy-on-fork-vmas-and-make-vm_maybe_guard-one.patch
queue-6.18/mm-introduce-vm_maybe_guard-and-make-visible-in-proc-pid-smaps.patch