linux-kernel - [PATCH 1/5] x86/mm: Do not flush last cacheline twice in clflush_cache

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Date:	Mon, 11 May 2015 10:15:49 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/5] x86/mm: Do not flush last cacheline twice in clflush_cache_range()

From: Ross Zwisler <ross.zwisler@...ux.intel.com>

The current algorithm used in clflush_cache_range() can cause the last
cache line of the buffer to be flushed twice. Fix that algorithm so that
each cache line will only be flushed once.

Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
Reported-by: H. Peter Anvin <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: x86-ml <x86@...nel.org>
Link: http://lkml.kernel.org/r/1430259192-18802-1-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/mm/pageattr.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 89af288ec674..338e507f95b8 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -129,16 +129,15 @@ within(unsigned long addr, unsigned long start, unsigned long end)
  */
 void clflush_cache_range(void *vaddr, unsigned int size)
 {
-	void *vend = vaddr + size - 1;
+	unsigned long clflush_mask = boot_cpu_data.x86_clflush_size - 1;
+	char *vend = (char *)vaddr + size;
+	char *p;
 
 	mb();
 
-	for (; vaddr < vend; vaddr += boot_cpu_data.x86_clflush_size)
-		clflushopt(vaddr);
-	/*
-	 * Flush any possible final partial cacheline:
-	 */
-	clflushopt(vend);
+	for (p = (char *)((unsigned long)vaddr & ~clflush_mask);
+	     p < vend; p += boot_cpu_data.x86_clflush_size)
+		clflushopt(p);
 
 	mb();
 }
-- 
2.3.5

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