This is a note to let you know that I've just added the patch titled
mm/shmem: use page_mapping() to detect page cache for uffd continue
to the 6.0-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-shmem-use-page_mapping-to-detect-page-cache-for-uffd-continue.patch
and it can be found in the queue-6.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 93b0d9178743a68723babe8448981f658aebc58e Mon Sep 17 00:00:00 2001
From: Peter Xu <peterx@xxxxxxxxxx>
Date: Wed, 2 Nov 2022 14:41:52 -0400
Subject: mm/shmem: use page_mapping() to detect page cache for uffd continue
From: Peter Xu <peterx@xxxxxxxxxx>
commit 93b0d9178743a68723babe8448981f658aebc58e upstream.
mfill_atomic_install_pte() checks page->mapping to detect whether one page
is used in the page cache. However as pointed out by Matthew, the page
can logically be a tail page rather than always the head in the case of
uffd minor mode with UFFDIO_CONTINUE. It means we could wrongly install
one pte with shmem thp tail page assuming it's an anonymous page.
It's not that clear even for anonymous page, since normally anonymous
pages also have page->mapping being setup with the anon vma. It's safe
here only because the only such caller to mfill_atomic_install_pte() is
always passing in a newly allocated page (mcopy_atomic_pte()), whose
page->mapping is not yet setup. However that's not extremely obvious
either.
For either of above, use page_mapping() instead.
Link: https://lkml.kernel.org/r/Y2K+y7wnhC4vbnP2@x1n
Fixes: 153132571f02 ("userfaultfd/shmem: support UFFDIO_CONTINUE for shmem")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reported-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/userfaultfd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -64,7 +64,7 @@ int mfill_atomic_install_pte(struct mm_s
pte_t _dst_pte, *dst_pte;
bool writable = dst_vma->vm_flags & VM_WRITE;
bool vm_shared = dst_vma->vm_flags & VM_SHARED;
- bool page_in_cache = page->mapping;
+ bool page_in_cache = page_mapping(page);
spinlock_t *ptl;
struct inode *inode;
pgoff_t offset, max_off;
Patches currently in stable-queue which might be from peterx@xxxxxxxxxx are
queue-6.0/mm-shmem-use-page_mapping-to-detect-page-cache-for-uffd-continue.patch
