FROMGIT: mm: prepare lock_vma_under_rcu() for vma reuse possibility

Once we make vma cache SLAB_TYPESAFE_BY_RCU, it will be possible for a vma
to be reused and attached to another mm after lock_vma_under_rcu() locks
the vma.  lock_vma_under_rcu() should ensure that vma_start_read() is
using the original mm and after locking the vma it should ensure that
vma->vm_mm has not changed from under us.

Link: https://lkml.kernel.org/r/20250213224655.1680278-17-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Shivank Garg <shivankg@amd.com>
  Link: https://lkml.kernel.org/r/5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Klara Modin <klarasmodin@gmail.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Sourav Panda <souravpanda@google.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit 920c585932bf97caab881f8f197c5a93c29c135c
https: //git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable)
Bug: 322132947
Change-Id: Ib14785a86242bb62a6788ae330f0217fb3187cb8
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

include/linux/mm.h

@@ -726,10 +726,13 @@ static inline void vma_refcount_put(struct vm_area_struct *vma)
  * Try to read-lock a vma. The function is allowed to occasionally yield false
  * locked result to avoid performance overhead, in which case we fall back to
  * using mmap_lock. The function should never yield false unlocked result.
+ * False locked result is possible if mm_lock_seq overflows or if vma gets
+ * reused and attached to a different mm before we lock it.
  * Returns the vma on success, NULL on failure to lock and EAGAIN if vma got
  * detached.
  */
-static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma)
+static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm,
+						    struct vm_area_struct *vma)
 {
 	int oldcnt;
 
@@ -740,7 +743,7 @@ static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma)
 	 * we don't rely on for anything - the mm_lock_seq read against which we
 	 * need ordering is below.
 	 */
-	if (READ_ONCE(vma->vm_lock_seq) == READ_ONCE(vma->vm_mm->mm_lock_seq.sequence))
+	if (READ_ONCE(vma->vm_lock_seq) == READ_ONCE(mm->mm_lock_seq.sequence))
 		return NULL;
 
 	/*
@@ -767,7 +770,7 @@ static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma)
 	 * after it has been unlocked.
 	 * This pairs with RELEASE semantics in vma_end_write_all().
 	 */
-	if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&vma->vm_mm->mm_lock_seq))) {
+	if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) {
 		vma_refcount_put(vma);
 		return NULL;
 	}
@@ -901,7 +904,8 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 #else /* CONFIG_PER_VMA_LOCK */
 
 static inline void vma_lock_init(struct vm_area_struct *vma, bool reset_refcnt) {}
-static inline struct vm_area_struct *vma_start_read(struct vm_area_struct *vma)
+static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm,
+						    struct vm_area_struct *vma)
 		{ return NULL; }
 static inline void vma_end_read(struct vm_area_struct *vma) {}
 static inline void vma_start_write(struct vm_area_struct *vma) {}

mm/memory.c

@@ -6333,7 +6333,7 @@ retry:
 	if (!vma)
 		goto inval;
 
-	vma = vma_start_read(vma);
+	vma = vma_start_read(mm, vma);
 	if (IS_ERR_OR_NULL(vma)) {
 		/* Check if the VMA got isolated after we found it */
 		if (PTR_ERR(vma) == -EAGAIN) {
@@ -6352,8 +6352,9 @@ retry:
 	 * fields are accessible for RCU readers.
 	 */
 
-	/* Check since vm_start/vm_end might change before we lock the VMA */
-	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
+	/* Check if the vma we locked is the right one. */
+	if (unlikely(vma->vm_mm != mm ||
+		     address < vma->vm_start || address >= vma->vm_end))
 		goto inval_end_read;
 
 	rcu_read_unlock();