From c2c37f5185ef80a770a9614f0317ad91b7672450 Mon Sep 17 00:00:00 2001 From: Kenneth Graunke Date: Sat, 1 Jul 2017 02:04:50 -0700 Subject: [PATCH] intel: Fix clflushing on modern (Baytrail+) Atom CPUs. Thanks to Chris Wilson for pointing this out. Reviewed-by: Daniel Vetter Reviewed-by: Matt Turner Acked-by: Lionel Landwerlin --- src/intel/common/gen_clflush.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/src/intel/common/gen_clflush.h b/src/intel/common/gen_clflush.h index 9b971cac37e..d39f15807eb 100644 --- a/src/intel/common/gen_clflush.h +++ b/src/intel/common/gen_clflush.h @@ -50,6 +50,18 @@ static inline void gen_invalidate_range(void *start, size_t size) { gen_clflush_range(start, size); + + /* Modern Atom CPUs (Baytrail+) have issues with clflush serialization, + * where mfence is not a sufficient synchronization barrier. We must + * double clflush the last cacheline. This guarantees it will be ordered + * after the preceding clflushes, and then the mfence guards against + * prefetches crossing the clflush boundary. + * + * See kernel commit 396f5d62d1a5fd99421855a08ffdef8edb43c76e + * ("drm: Restore double clflush on the last partial cacheline") + * and https://bugs.freedesktop.org/show_bug.cgi?id=92845. + */ + __builtin_ia32_clflush(start + size - 1); __builtin_ia32_mfence(); } -- 2.30.2