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5543d3c43c
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: 86039bd3b4 ("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.