4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
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@xxxxxxxxx>
Suggested-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Tested-by: Olaf Hering <olaf@xxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/xen/gntdev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -804,7 +804,7 @@ 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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