linux-kernel - [PATCH 03 of 36] x86: add memory barriers to wrmsr

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Date:	Wed, 25 Jun 2008 00:18:59 -0400
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	xen-devel <xen-devel@...ts.xensource.com>,
	Stephen Tweedie <sct@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Mark McLoughlin <markmc@...hat.com>, x86@...nel.org
Subject: [PATCH 03 of 36] x86: add memory barriers to wrmsr

wrmsr is a special instruction which can have arbitrary system-wide
effects.  We don't want the compiler to reorder it with respect to
memory operations, so make it a memory barrier.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 include/asm-x86/msr.h |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/asm-x86/msr.h b/include/asm-x86/msr.h
--- a/include/asm-x86/msr.h
+++ b/include/asm-x86/msr.h
@@ -66,7 +66,7 @@
 static inline void native_write_msr(unsigned int msr,
 				    unsigned low, unsigned high)
 {
-	asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high));
+	asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high) : "memory");
 }
 
 static inline int native_write_msr_safe(unsigned int msr,
@@ -81,7 +81,8 @@
 		     _ASM_EXTABLE(2b, 3b)
 		     : "=a" (err)
 		     : "c" (msr), "0" (low), "d" (high),
-		     "i" (-EFAULT));
+		       "i" (-EFAULT)
+		     : "memory");
 	return err;
 }
 


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