vhost: fix get_user_pages_fast error handling

get_user_pages_fast returns number of pages on success, negative value
on failure, but never 0. Fix vhost code to match this logic.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 6c31c0c9bbb..7cd55e07879 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -646,8 +646,9 @@ static int set_bit_to_user(int nr, void __user *addr)
         int bit = nr + (log % PAGE_SIZE) * 8;
         int r;
         r = get_user_pages_fast(log, 1, 1, &page);
-        if (r)
+        if (r < 0)
                 return r;
+        BUG_ON(r != 1);
         base = kmap_atomic(page, KM_USER0);
         set_bit(bit, base);
         kunmap_atomic(base, KM_USER0);