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

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>
Cc: <stable@kernel.org> # .39.x
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 3 deletions

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 6f9d1f6063e9..8f5cabb3c5b0 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -629,10 +629,13 @@ 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);
+                }
         }
 }