[tip:x86/cpu] x86: Use clflushopt in drm_clflush_page

[tip-bot for Ross Zwisler]

Commit-ID:  2a0c772f1967565d5b71a98012e74d5a7bddc1c4
Gitweb:     http://git.kernel.org/tip/2a0c772f1967565d5b71a98012e74d5a7bddc1c4
Author:     Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
AuthorDate: Wed, 26 Feb 2014 12:06:51 -0700
Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Thu, 27 Feb 2014 08:26:20 -0800

x86: Use clflushopt in drm_clflush_page

If clflushopt is available on the system, use it instead of clflush in
drm_clflush_page.

Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1393441612-19729-4-git-send-email-ross.zwisler@xxxxxxxxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_cache.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index bb8f580..c518fb6 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -32,6 +32,12 @@
 #include <drm/drmP.h>
 
 #if defined(CONFIG_X86)
+
+/*
+ * clflushopt is an unordered instruction which needs fencing with mfence or
+ * sfence to avoid ordering issues.  For drm_clflush_page this fencing happens
+ * in the caller.
+ */
 static void
 drm_clflush_page(struct page *page)
 {
@@ -44,7 +50,7 @@ drm_clflush_page(struct page *page)
 
 	page_virtual = kmap_atomic(page);
 	for (i = 0; i < PAGE_SIZE; i += size)
-		clflush(page_virtual + i);
+		clflushopt(page_virtual + i);
 	kunmap_atomic(page_virtual);
 }
 
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