Refuse to allocate giant BOs on 32-bit systems.

The overcommit of address space combined with these buffers hitting SW
fallbacks all the time means that we're probably better off telling the
application "no" instead of likely silently failing later.

Bug #22601.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/i830_uxa.c b/src/i830_uxa.c
index eb35014e..ef7ac84a 100644
--- a/src/i830_uxa.c
+++ b/src/i830_uxa.c
@@ -627,6 +627,22 @@ i830_uxa_create_pixmap (ScreenPtr screen, int w, int h, int depth, unsigned usag
 	     * with drm_intel_bufmgr_check_aperture().
 	     */
 	    size = i830_get_fence_size(i830, stride * h);
+	    assert(size >= stride * h);
+	}
+
+	/* Fail very large allocations on 32-bit systems.  Large BOs will
+	 * tend to hit SW fallbacks frequently, and also will tend to fail
+	 * to successfully map when doing SW fallbacks because we overcommit
+	 * address space for BO access.
+	 *
+	 * Note that size should fit in 32 bits.  We throw out >32767x32767x4,
+	 * and pitch alignment could get us up to 32768x32767x4.
+	 */
+	if (sizeof(unsigned int) == 4 &&
+	    size > (unsigned int)(1024 * 1024 * 1024))
+	{
+	    fbDestroyPixmap (pixmap);
+	    return NullPixmap;
 	}
 
 	bo = drm_intel_bo_alloc_for_render(i830->bufmgr, "pixmap", size, 0);