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authorAxel Rasmussen <axelrasmussen@google.com>2022-06-10 20:38:12 +0300
committerakpm <akpm@linux-foundation.org>2022-07-04 01:42:32 +0300
commit73f37dbcfe1763ee2294c7717a1f571e27d17fd8 (patch)
tree9aa244594be59eeb038b115708db562bc3d2b114 /mm/userfaultfd.c
parent03c765b0e3b4cb5063276b086c76f7a612856a9a (diff)
downloadlinux-73f37dbcfe1763ee2294c7717a1f571e27d17fd8.tar.xz
mm: userfaultfd: fix UFFDIO_CONTINUE on fallocated shmem pages
When fallocate() is used on a shmem file, the pages we allocate can end up with !PageUptodate. Since UFFDIO_CONTINUE tries to find the existing page the user wants to map with SGP_READ, we would fail to find such a page, since shmem_getpage_gfp returns with a "NULL" pagep for SGP_READ if it discovers !PageUptodate. As a result, UFFDIO_CONTINUE returns -EFAULT, as it would do if the page wasn't found in the page cache at all. This isn't the intended behavior. UFFDIO_CONTINUE is just trying to find if a page exists, and doesn't care whether it still needs to be cleared or not. So, instead of SGP_READ, pass in SGP_NOALLOC. This is the same, except for one critical difference: in the !PageUptodate case, SGP_NOALLOC will clear the page and then return it. With this change, UFFDIO_CONTINUE works properly (succeeds) on a shmem file which has been fallocated, but otherwise not modified. Link: https://lkml.kernel.org/r/20220610173812.1768919-1-axelrasmussen@google.com Fixes: 153132571f02 ("userfaultfd/shmem: support UFFDIO_CONTINUE for shmem") Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: Peter Xu <peterx@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/userfaultfd.c')
-rw-r--r--mm/userfaultfd.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 4f4892a5f767..07d3befc80e4 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -246,7 +246,10 @@ static int mcontinue_atomic_pte(struct mm_struct *dst_mm,
struct page *page;
int ret;
- ret = shmem_getpage(inode, pgoff, &page, SGP_READ);
+ ret = shmem_getpage(inode, pgoff, &page, SGP_NOALLOC);
+ /* Our caller expects us to return -EFAULT if we failed to find page. */
+ if (ret == -ENOENT)
+ ret = -EFAULT;
if (ret)
goto out;
if (!page) {