From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Maxim Levitsky <mlevitsk@redhat.com>
Subject: [PATCH v2 06/21] KVM: nSVM: Skip writes to MSR_AMD64_TSC_RATIO if guest state isn't loaded
Date: Fri, 28 Jul 2023 18:15:53 -0700 [thread overview]
Message-ID: <20230729011608.1065019-7-seanjc@google.com> (raw)
In-Reply-To: <20230729011608.1065019-1-seanjc@google.com>
Skip writes to MSR_AMD64_TSC_RATIO that are done in the context of a vCPU
if guest state isn't loaded, i.e. if KVM will update MSR_AMD64_TSC_RATIO
during svm_prepare_switch_to_guest() before entering the guest. Checking
guest_state_loaded may or may not be a net positive for performance as
the current_tsc_ratio cache will optimize away duplicate WRMSRs in the
vast majority of scenarios. However, the cost of the check is negligible,
and the real motivation is to document that KVM needs to load the vCPU's
value only when running the vCPU.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/svm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c786c8e9108f..64092df06f94 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1109,7 +1109,8 @@ static void svm_write_tsc_offset(struct kvm_vcpu *vcpu)
void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu)
{
preempt_disable();
- __svm_write_tsc_multiplier(vcpu->arch.tsc_scaling_ratio);
+ if (to_svm(vcpu)->guest_state_loaded)
+ __svm_write_tsc_multiplier(vcpu->arch.tsc_scaling_ratio);
preempt_enable();
}
--
2.41.0.487.g6d72f3e995-goog
next prev parent reply other threads:[~2023-07-29 1:16 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-29 1:15 [PATCH v2 00/21] KVM: x86: Add "governed" X86_FEATURE framework Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 01/21] KVM: nSVM: Check instead of asserting on nested TSC scaling support Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 02/21] KVM: nSVM: Load L1's TSC multiplier based on L1 state, not L2 state Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 03/21] KVM: nSVM: Use the "outer" helper for writing multiplier to MSR_AMD64_TSC_RATIO Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 04/21] KVM: SVM: Clean up preemption toggling related " Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 05/21] KVM: x86: Always write vCPU's current TSC offset/ratio in vendor hooks Sean Christopherson
2023-07-29 1:15 ` Sean Christopherson [this message]
2023-07-29 1:15 ` [PATCH v2 07/21] KVM: x86: Add a framework for enabling KVM-governed x86 features Sean Christopherson
2023-08-14 4:43 ` Zeng Guang
2023-08-14 17:20 ` Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 08/21] KVM: x86/mmu: Use KVM-governed feature framework to track "GBPAGES enabled" Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 09/21] KVM: VMX: Recompute "XSAVES enabled" only after CPUID update Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 10/21] KVM: VMX: Check KVM CPU caps, not just VMX MSR support, for XSAVE enabling Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 11/21] KVM: VMX: Rename XSAVES control to follow KVM's preferred "ENABLE_XYZ" Sean Christopherson
2023-07-29 1:15 ` [PATCH v2 12/21] KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled" Sean Christopherson
2023-08-14 6:28 ` Zeng Guang
2023-07-29 1:16 ` [PATCH v2 13/21] KVM: nVMX: Use KVM-governed feature framework to track "nested VMX enabled" Sean Christopherson
2023-08-14 8:11 ` Yuan Yao
2023-07-29 1:16 ` [PATCH v2 14/21] KVM: nSVM: Use KVM-governed feature framework to track "NRIPS enabled" Sean Christopherson
2023-07-29 1:16 ` [PATCH v2 15/21] KVM: nSVM: Use KVM-governed feature framework to track "TSC scaling enabled" Sean Christopherson
2023-07-29 1:16 ` [PATCH v2 16/21] KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD} enabled" Sean Christopherson
2023-07-29 1:16 ` [PATCH v2 17/21] KVM: nSVM: Use KVM-governed feature framework to track "LBRv enabled" Sean Christopherson
2023-07-29 1:16 ` [PATCH v2 18/21] KVM: nSVM: Use KVM-governed feature framework to track "Pause Filter enabled" Sean Christopherson
2023-07-29 1:16 ` [PATCH v2 19/21] KVM: nSVM: Use KVM-governed feature framework to track "vGIF enabled" Sean Christopherson
2023-07-29 1:16 ` [PATCH v2 20/21] KVM: nSVM: Use KVM-governed feature framework to track "vNMI enabled" Sean Christopherson
2023-07-29 1:16 ` [PATCH v2 21/21] KVM: x86: Disallow guest CPUID lookups when IRQs are disabled Sean Christopherson
2023-08-04 0:40 ` [PATCH v2 00/21] KVM: x86: Add "governed" X86_FEATURE framework Sean Christopherson
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