linux-kernel - [PATCH] [2/99] x86, amd: Use _safe() msr access for GartTlbWlk disable code

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Message-Id: <20110727214800.5CA142403FF@tassilo.jf.intel.com>
Date:	Wed, 27 Jul 2011 14:48:00 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	Joerg.Roedel@....com, joerg.roedel@....com, rjw@...k.pl,
	maciej.rutecki@...il.com, avi@...hat.com,
	akpm@...ux-foundation.org, mingo@...e.hu, gregkh@...e.de,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	stable@...nel.org, tim.bird@...sony.com
Subject: [PATCH] [2/99] x86, amd: Use _safe() msr access for GartTlbWlk disable code

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: "Roedel, Joerg" <Joerg.Roedel@....com>

commit d47cc0db8fd6011de2248df505fc34990b7451bf upstream.

The workaround for Bugzilla:

	https://bugzilla.kernel.org/show_bug.cgi?id=33012

introduced a read and a write to the MC4 mask msr.

Unfortunatly this MSR is not emulated by the KVM hypervisor
so that the kernel will get a #GP and crashes when applying
this workaround when running inside KVM.

This issue was reported as:

	https://bugzilla.kernel.org/show_bug.cgi?id=35132

and is fixed with this patch. The change just let the kernel
ignore any #GP it gets while accessing this MSR by using the
_safe msr access methods.

Reported-by: Török Edwin <edwintorok@...il.com>
Signed-off-by: Joerg Roedel <joerg.roedel@....com>
Cc: Rafael J. Wysocki <rjw@...k.pl>
Cc: Maciej Rutecki <maciej.rutecki@...il.com>
Cc: Avi Kivity <avi@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 arch/x86/kernel/cpu/amd.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Index: linux-2.6.35.y/arch/x86/kernel/cpu/amd.c
===================================================================
--- linux-2.6.35.y.orig/arch/x86/kernel/cpu/amd.c
+++ linux-2.6.35.y/arch/x86/kernel/cpu/amd.c
@@ -585,10 +585,13 @@ static void __cpuinit init_amd(struct cp
 		 * Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=33012
 		 */
 		u64 mask;
+		int err;

-		rdmsrl(MSR_AMD64_MCx_MASK(4), mask);
-		mask |= (1 << 10);
-		wrmsrl(MSR_AMD64_MCx_MASK(4), mask);
+		err = rdmsrl_safe(MSR_AMD64_MCx_MASK(4), &mask);
+		if (err == 0) {
+			mask |= (1 << 10);
+			checking_wrmsrl(MSR_AMD64_MCx_MASK(4), mask);
+		}
 	}
 }

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