diff mbox series

[3/3] KVM: x86/pmu: Drop redundant-clumsy-asymmetric PERFCTR_CORE MSRs handling

Message ID 20220509102204.62389-3-likexu@tencent.com (mailing list archive)
State New, archived
Headers show
Series [1/3] KVM: x86/pmu: Ignore pmu->global_ctrl check if vPMU doesn't support global_ctrl | expand

Commit Message

Like Xu May 9, 2022, 10:22 a.m. UTC 
From: Like Xu <likexu@tencent.com>

In commit c51eb52b8f98 ("KVM: x86: Add support for AMD Core Perf Extension
in guest"), the entry "case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5 " is
introduced asymmetrically into kvm_get_msr_common(), ignoring the set part.

The missing guest PERFCTR_CORE cpuid check from the above commit leads to
the commit c28fa560c5bb ("KVM: x86/vPMU: Forbid reading from MSR_F15H_PERF
MSRs when guest doesn't have X86_FEATURE_PERFCTR_CORE"), but it simply
duplicates the default entry at the end of the switch statement explicitly.

Removing the PERFCTR_CORE MSRs entry in kvm_get_msr_common() thoroughly
would be more maintainable, as we did for the same group of MSRs in the
kvm_set_msr_common() at the very beginning when the feature was enabled.

Signed-off-by: Like Xu <likexu@tencent.com>
---
 arch/x86/kvm/x86.c | 7 -------
 1 file changed, 7 deletions(-)

Comments

Paolo Bonzini May 20, 2022, 2:32 p.m. UTC | #1 
On 5/9/22 12:22, Like Xu wrote:
> In commit c51eb52b8f98 ("KVM: x86: Add support for AMD Core Perf Extension
> in guest"), the entry "case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5 " is
> introduced asymmetrically into kvm_get_msr_common(), ignoring the set part.
> 
> The missing guest PERFCTR_CORE cpuid check from the above commit leads to
> the commit c28fa560c5bb ("KVM: x86/vPMU: Forbid reading from MSR_F15H_PERF
> MSRs when guest doesn't have X86_FEATURE_PERFCTR_CORE"), but it simply
> duplicates the default entry at the end of the switch statement explicitly.
> 
> Removing the PERFCTR_CORE MSRs entry in kvm_get_msr_common() thoroughly
> would be more maintainable, as we did for the same group of MSRs in the
> kvm_set_msr_common() at the very beginning when the feature was enabled.

The code and the commit message suggest that some guests are expecting a 
#GP, and complain if they don't get it.

Paolo
diff mbox series

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4790f0d7d40b..2b9089701ef5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3841,13 +3841,6 @@  int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_DRAM_ENERGY_STATUS:	/* DRAM controller */
 		msr_info->data = 0;
 		break;
-	case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
-		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
-			return kvm_pmu_get_msr(vcpu, msr_info);
-		if (!msr_info->host_initiated)
-			return 1;
-		msr_info->data = 0;
-		break;
 	case MSR_K7_EVNTSEL0 ... MSR_K7_EVNTSEL3:
 	case MSR_K7_PERFCTR0 ... MSR_K7_PERFCTR3:
 	case MSR_P6_PERFCTR0 ... MSR_P6_PERFCTR1: