https://github.com/torvalds/linux
Revision 5b51072e97d587186c2f5390c8c9c1fb7e179505 authored by Andrea Arcangeli on 30 November 2018, 22:09:28 UTC, committed by Linus Torvalds on 30 November 2018, 22:56:14 UTC
Userfaultfd did not create private memory when UFFDIO_COPY was invoked on a MAP_PRIVATE shmem mapping. Instead it wrote to the shmem file, even when that had not been opened for writing. Though, fortunately, that could only happen where there was a hole in the file. Fix the shmem-backed implementation of UFFDIO_COPY to create private memory for MAP_PRIVATE mappings. The hugetlbfs-backed implementation was already correct. This change is visible to userland, if userfaultfd has been used in unintended ways: so it introduces a small risk of incompatibility, but is necessary in order to respect file permissions. An app that uses UFFDIO_COPY for anything like postcopy live migration won't notice the difference, and in fact it'll run faster because there will be no copy-on-write and memory waste in the tmpfs pagecache anymore. Userfaults on MAP_PRIVATE shmem keep triggering only on file holes like before. The real zeropage can also be built on a MAP_PRIVATE shmem mapping through UFFDIO_ZEROPAGE and that's safe because the zeropage pte is never dirty, in turn even an mprotect upgrading the vma permission from PROT_READ to PROT_READ|PROT_WRITE won't make the zeropage pte writable. Link: http://lkml.kernel.org/r/20181126173452.26955-3-aarcange@redhat.com Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support") Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reported-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: Hugh Dickins <hughd@google.com> Cc: <stable@vger.kernel.org> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Tip revision: 5b51072e97d587186c2f5390c8c9c1fb7e179505 authored by Andrea Arcangeli on 30 November 2018, 22:09:28 UTC
userfaultfd: shmem: allocate anonymous memory for MAP_PRIVATE shmem
userfaultfd: shmem: allocate anonymous memory for MAP_PRIVATE shmem
Tip revision: 5b51072
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.cocciconfig | -rw-r--r-- | 59 bytes |
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COPYING | -rw-r--r-- | 423 bytes |
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Kbuild | -rw-r--r-- | 2.2 KB |
Kconfig | -rw-r--r-- | 563 bytes |
MAINTAINERS | -rw-r--r-- | 472.8 KB |
Makefile | -rw-r--r-- | 59.7 KB |
README | -rw-r--r-- | 727 bytes |
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