From: Roedel, Joerg <Joerg.Roedel@amd.com>
Date: Thu, 19 May 2011 09:13:39 +0000 (+0200)
Subject: x86, amd: Use _safe() msr access for GartTlbWlk disable code
X-Git-Url: http://git.alex.org.uk

x86, amd: Use _safe() msr access for GartTlbWlk disable code

BugLink: http://bugs.launchpad.net/bugs/793702

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@gmail.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Maciej Rutecki <maciej.rutecki@gmail.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index ae2be9a..e19776f 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -615,10 +615,13 @@ 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);
+		}
 	}
 }