linux-kernel - [PATCH] x86: improve algorithm in clflush_cache

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Message-Id: <1430259192-18802-1-git-send-email-ross.zwisler@linux.intel.com>
Date:	Tue, 28 Apr 2015 16:13:12 -0600
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Cc:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Borislav Petkov <bp@...e.de>
Subject: [PATCH] x86: improve algorithm in clflush_cache_range

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: H. Peter Anvin <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: x86@...nel.org
Cc: 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();
 }
-- 
1.9.3

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