intel-agp: fix a panic with 1M of shared memory, no GTT entries

When GTT size is equal to amount of video memory, the amount of GTT
entries is computed lower than zero, which is invalid and leads to
off-by-one error in intel_i915_configure()

Originally posted here:
http://bugzilla.kernel.org/show_bug.cgi?id=12539
http://bugzilla.redhat.com/show_bug.cgi?id=445592

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Cc: Lubomir Rintel <lkundrak@v3.sk>
Cc: Dave Airlie <airlied@linux.ie>
Reviewed-by: Eric Anholt <eric@anholt.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index c7714185f83103219de72565f34a3dadbb6e198d..4373adb2119aeea256758abc7602504477d5c5ad 100644 (file)
--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -633,13 +633,15 @@ static void intel_i830_init_gtt_entries(void)
                        break;
                }
        }
-       if (gtt_entries > 0)
+       if (gtt_entries > 0) {
                dev_info(&agp_bridge->dev->dev, "detected %dK %s memory\n",
                       gtt_entries / KB(1), local ? "local" : "stolen");
-       else
+               gtt_entries /= KB(4);
+       } else {
                dev_info(&agp_bridge->dev->dev,
                       "no pre-allocated video memory detected\n");
-       gtt_entries /= KB(4);
+               gtt_entries = 0;
+       }
 
        intel_private.gtt_entries = gtt_entries;
 }