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    Subject[PATCH 3.16 056/370] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing
    3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Boris Ostrovsky <boris.ostrovsky@oracle.com>

    commit 30faaafdfa0c754c91bac60f216c9f34a2bfdf7e upstream.

    Commit 9c17d96500f7 ("xen/gntdev: Grant maps should not be subject to
    NUMA balancing") set VM_IO flag to prevent grant maps from being
    subjected to NUMA balancing.

    It was discovered recently that this flag causes get_user_pages() to
    always fail with -EFAULT.

    check_vma_flags
    __get_user_pages
    __get_user_pages_locked
    __get_user_pages_unlocked
    get_user_pages_fast
    iov_iter_get_pages
    dio_refill_pages
    do_direct_IO
    do_blockdev_direct_IO
    do_blockdev_direct_IO
    ext4_direct_IO_read
    generic_file_read_iter
    aio_run_iocb

    (which can happen if guest's vdisk has direct-io-safe option).

    To avoid this let's use VM_MIXEDMAP flag instead --- it prevents
    NUMA balancing just as VM_IO does and has no effect on
    check_vma_flags().


    Reported-by: Olaf Hering <olaf@aepfle.de>
    Suggested-by: Hugh Dickins <hughd@google.com>
    Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Acked-by: Hugh Dickins <hughd@google.com>
    Tested-by: Olaf Hering <olaf@aepfle.de>
    Signed-off-by: Juergen Gross <jgross@suse.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/xen/gntdev.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/xen/gntdev.c
    +++ b/drivers/xen/gntdev.c
    @@ -765,7 +765,7 @@ static int gntdev_mmap(struct file *flip

    vma->vm_ops = &gntdev_vmops;

    - vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
    + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;

    if (use_ptemod)
    vma->vm_flags |= VM_DONTCOPY;
    \
     
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