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authorPeter Xu <peterx@redhat.com>2023-05-17 15:09:16 -0400
committerAndrew Morton <akpm@linux-foundation.org>2023-06-12 11:31:50 -0700
commit5543d3c43c41a8501f2a4946d0fd39ce36b5a641 (patch)
treef3ef598c5c7bb68e757bc1108eb0a5cd96871849 /fs
parent270aa010620697fb27b8f892cc4e194bc2b7d134 (diff)
mm/uffd: allow vma to merge as much as possible
We used to not pass in the pgoff correctly when register/unregister uffd regions, it caused incorrect behavior on vma merging and can cause mergeable vmas being separate after ioctls return. For example, when we have: vma1(range 0-9, with uffd), vma2(range 10-19, no uffd) Then someone unregisters uffd on range (5-9), it should logically become: vma1(range 0-4, with uffd), vma2(range 5-19, no uffd) But with current code we'll have: vma1(range 0-4, with uffd), vma3(range 5-9, no uffd), vma2(range 10-19, no uffd) This patch allows such merge to happen correctly before ioctl returns. This behavior seems to have existed since the 1st day of uffd. Since pgoff for vma_merge() is only used to identify the possibility of vma merging, meanwhile here what we did was always passing in a pgoff smaller than what we should, so there should have no other side effect besides not merging it. Let's still tentatively copy stable for this, even though I don't see anything will go wrong besides vma being split (which is mostly not user visible). Link: https://lkml.kernel.org/r/20230517190916.3429499-3-peterx@redhat.com Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") Signed-off-by: Peter Xu <peterx@redhat.com> Reported-by: Lorenzo Stoakes <lstoakes@gmail.com> Acked-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/userfaultfd.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 17c8c345dac4..4e800bb7d2ab 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1332,6 +1332,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
bool basic_ioctls;
unsigned long start, end, vma_end;
struct vma_iterator vmi;
+ pgoff_t pgoff;
user_uffdio_register = (struct uffdio_register __user *) arg;
@@ -1484,8 +1485,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
vma_end = min(end, vma->vm_end);
new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
+ pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags,
- vma->anon_vma, vma->vm_file, vma->vm_pgoff,
+ vma->anon_vma, vma->vm_file, pgoff,
vma_policy(vma),
((struct vm_userfaultfd_ctx){ ctx }),
anon_vma_name(vma));
@@ -1565,6 +1567,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
unsigned long start, end, vma_end;
const void __user *buf = (void __user *)arg;
struct vma_iterator vmi;
+ pgoff_t pgoff;
ret = -EFAULT;
if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
@@ -1667,8 +1670,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
uffd_wp_range(vma, start, vma_end - start, false);
new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
+ pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags,
- vma->anon_vma, vma->vm_file, vma->vm_pgoff,
+ vma->anon_vma, vma->vm_file, pgoff,
vma_policy(vma),
NULL_VM_UFFD_CTX, anon_vma_name(vma));
if (prev) {