linux-kernel - [34-longterm 015/179] x86, amd: Use _safe() msr access for GartTlbWlk disable code

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Message-ID: <1337048075-6132-16-git-send-email-paul.gortmaker@windriver.com>
Date:	Mon, 14 May 2012 22:11:51 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	<stable@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: [34-longterm 015/179] x86, amd: Use _safe() msr access for GartTlbWlk disable code

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

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

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: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 arch/x86/kernel/cpu/amd.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 770346d..02a5a5f 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -586,10 +586,13 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
 		 * 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);
+		}
 	}
 }
 
-- 
1.7.9.6

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