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

commit 9c1e8a4ebcc04226cb6f3a1bf1d72f4cafd6b089 upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index 5eb23fa48bbf3ebb4bfb6c8993ff02ed2b221a65..c052627423dae7e867a4392e09ee961c24eae0c2 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;
 }