Re: [PATCH]: Fix MSR_K7_EVNTSEL{0,3} for SVM

[Chris Lalancette <clalance@redhat.com>]

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Joerg Roedel wrote:
> We already discussed the emulation of the performance counter registers
> in the past. The conclusion is, that we loose live migration with that
> emulation because performance monitoring is implemented differently
> between AMD and Intel systems. Maybe discarding _any_ writes to
> the performance counter MSRs will fix the guest crash. What we should
> not do is injecting GPF on zero writes to the MSRs because that will
> break Windows XP 64bit installation.

     OK, yeah, I read some of those threads over the weekend.  It is a larger
problem than just this crash, and probably one to be solved later.
     I have attached a patch which just discards all writes, as you suggested;
this allows my RHEL-4 guest to successfully boot, although obviously the NMI
watchdog which it thinks it set up is not actually working.  Joerg, can you test
this on your 64-bit Windows XP guest to make sure it is still working?

Thanks,
Chris Lalancette

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diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 89e0be2..6130704 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1284,16 +1284,18 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, unsigned ecx, u64 data)
 	case MSR_K7_EVNTSEL1:
 	case MSR_K7_EVNTSEL2:
 	case MSR_K7_EVNTSEL3:
+	case MSR_K7_PERFCTR0:
+	case MSR_K7_PERFCTR1:
+	case MSR_K7_PERFCTR2:
+	case MSR_K7_PERFCTR3:
 		/*
-		 * only support writing 0 to the performance counters for now
-		 * to make Windows happy. Should be replaced by a real
-		 * performance counter emulation later.
+		 * Just discard all writes to the performance counters; this
+		 * should keep both older linux and windows 64-bit guests
+		 * happy
 		 */
-		if (data != 0)
-			goto unhandled;
+
 		break;
 	default:
-	unhandled:
 		return kvm_set_msr_common(vcpu, ecx, data);
 	}
 	return 0;

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