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Subject[PATCH 3.16 292/305] KVM: Handle MSR_IA32_PERF_CTL
3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dmitry Bilunov <kmeaw@yandex-team.ru>

commit 0c2df2a1affd183ba9c114915f42a2d464b4f58f upstream.

Intel CPUs having Turbo Boost feature implement an MSR to provide a
control interface via rdmsr/wrmsr instructions. One could detect the
presence of this feature by issuing one of these instructions and
handling the #GP exception which is generated in case the referenced MSR
is not implemented by the CPU.

KVM's vCPU model behaves exactly as a real CPU in this case by injecting
a fault when MSR_IA32_PERF_CTL is called (which KVM does not support).
However, some operating systems use this register during an early boot
stage in which their kernel is not capable of handling #GP correctly,
causing #DP and finally a triple fault effectively resetting the vCPU.

This patch implements a dummy handler for MSR_IA32_PERF_CTL to avoid the
crashes.

Signed-off-by: Dmitry Bilunov <kmeaw@yandex-team.ru>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/x86/kvm/x86.c | 1 +
1 file changed, 1 insertion(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2461,6 +2461,7 @@ int kvm_get_msr_common(struct kvm_vcpu *
case MSR_AMD64_NB_CFG:
case MSR_FAM10H_MMIO_CONF_BASE:
case MSR_AMD64_BU_CFG2:
+ case MSR_IA32_PERF_CTL:
msr_info->data = 0;
break;
case MSR_P6_PERFCTR0:
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