4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Chris Wilson <ch...@chris-wilson.co.uk> commit 396f5d62d1a5fd99421855a08ffdef8edb43c76e upstream. This effectively reverts commit afcd950cafea6e27b739fe7772cbbeed37d05b8b Author: Chris Wilson <chris at chris-wilson.co.uk> Date: Wed Jun 10 15:58:01 2015 +0100 drm: Avoid the double clflush on the last cache line in drm_clflush_virt_range() as we have observed issues with serialisation of the clflush operations on Baytrail+ Atoms with partial updates. Applying the double flush on the last cacheline forces that clflush to be ordered with respect to the previous clflush, and the mfence then protects against prefetches crossing the clflush boundary. The same issue can be demonstrated in userspace with igt/gem_exec_flush. Fixes: afcd950cafea6 (drm: Avoid the double clflush on the last cache...) Testcase: igt/gem_concurrent_blit Testcase: igt/gem_partial_pread_pwrite Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92845 Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk> Cc: dri-devel at lists.freedesktop.org Cc: Akash Goel <akash.goel at intel.com> Cc: Imre Deak <imre.deak at intel.com> Cc: Daniel Vetter <daniel.vetter at ffwll.ch> Cc: Jason Ekstrand <jason.ekstrand at intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala at intel.com> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/1467880930-23082-6-git-send-email-chris at chris-wilson.co.uk Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org> --- drivers/gpu/drm/drm_cache.c | 1 + 1 file changed, 1 insertion(+) --- a/drivers/gpu/drm/drm_cache.c +++ b/drivers/gpu/drm/drm_cache.c @@ -136,6 +136,7 @@ drm_clflush_virt_range(void *addr, unsig mb(); for (; addr < end; addr += size) clflushopt(addr); + clflushopt(end - 1); /* force serialisation */ mb(); return; }