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

From: Paul Gortmaker
Date: Mon May 14 2012 - 22:51:50 EST

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

This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.

commit d47cc0db8fd6011de2248df505fc34990b7451bf upstream.

The workaround for Bugzilla:


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:


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: TÃrÃk Edwin <edwintorok@xxxxxxxxx>
Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx>
Cc: Rafael J. Wysocki <rjw@xxxxxxx>
Cc: Maciej Rutecki <maciej.rutecki@xxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
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);
+ }


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