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>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 6c31c0c9bbb9fb315d76ea807073eb8526648e3a..7cd55e07879455abe95e04fa06656623b415c9a9 100644 (file)
--- 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);