linux-kernel - [PATCH 3.12 041/235] xen/gntdev: Use VM_MIXEDMAP instead of VM

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Message-Id: <7c5f94349ac6b14a42469bc0909e63a0e77cdb21.1485514374.git.jslaby@suse.cz>
Date:   Fri, 27 Jan 2017 11:52:54 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 041/235] xen/gntdev: Use VM_MIXEDMAP instead of VM_IO to avoid NUMA balancing

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

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...fle.de>
Suggested-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Acked-by: Hugh Dickins <hughd@...gle.com>
Tested-by: Olaf Hering <olaf@...fle.de>
Signed-off-by: Juergen Gross <jgross@...e.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 27accc4cc999..c17116f63eb1 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -763,7 +763,7 @@ 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;
-- 
2.11.0