From d6db3f5c11dc7ed5712d5d5682aa34025ee5248e Mon Sep 17 00:00:00 2001
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Tue, 23 Feb 2010 11:25:23 +0200
Subject: 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 6c31c0c..7cd55e0 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);
-- 
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