[PATCH 3.10 060/268] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

Willy Tarreau
2017-06-19T19:33:47Z

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: Willy Tarreau <w@1wt.eu>
---
drivers/xen/gntdev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 3d8e609..6c6d253 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -770,7 +770,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)

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;
--
2.8.0.rc2.1.gbe9624a