Patch "xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xen-gntdev-use-vm_mixedmap-instead-of-vm_io-to-avoid-numa-balancing.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Boris Ostrovsky <[email protected]>
Date: Mon, 21 Nov 2016 09:56:06 -0500
Subject: xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

From: Boris Ostrovsky <[email protected]>

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().

---
 drivers/xen/gntdev.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/xen-gntdev-use-vm_mixedmap-instead-of-vm_io-to-avoid-numa-balancing.patch