vhost: use USER_DS in vhost_worker thread

On some architectures address spaces are set up in a way that this is
not necessary to work properly but on some others (like s390) it is.
Make sure we operate on the user address space to allow copy_xxx_user()
from the vhost_worker() thread by setting it explicitly before calling
use_mm() and revert it after unuse_mm().

Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 94dbd25caa30..112156f68afb 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -191,7 +191,9 @@ static int vhost_worker(void *data)
         struct vhost_dev *dev = data;
         struct vhost_work *work = NULL;
         unsigned uninitialized_var(seq);
+        mm_segment_t oldfs = get_fs();
 
+        set_fs(USER_DS);
         use_mm(dev->mm);
 
         for (;;) {
@@ -229,6 +231,7 @@ static int vhost_worker(void *data)
 
         }
         unuse_mm(dev->mm);
+        set_fs(oldfs);
         return 0;
 }