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

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: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 770346d348c23f75827f421930fecb827b75446b..02a5a5f6a6c1f4c2e2395f41387abb232b560129 100644 (file)
--- 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);
+               }
        }
 }