linux-kernel - [PATCH] KVM: x86: Track supported ARCH_CAPABILITIES in kvm

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Date:   Sat,  6 May 2023 11:04:35 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     kvm@...r.kernel.org
Cc:     Chao Gao <chao.gao@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86: Track supported ARCH_CAPABILITIES in kvm_caps

to avoid computing the supported value at runtime every time.

No functional change intended.

Signed-off-by: Chao Gao <chao.gao@...el.com>
---

A new call site of kvm_get_arch_capabilities() is added by [1]. It should be
replaced with the cached value in kvm_caps.

[1] https://lore.kernel.org/all/20230504181827.130532-1-mizhang@google.com/


 arch/x86/kvm/x86.c | 5 +++--
 arch/x86/kvm/x86.h | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 523c39a03c00..94aa70ec169c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1670,7 +1670,7 @@ static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
 {
 	switch (msr->index) {
 	case MSR_IA32_ARCH_CAPABILITIES:
-		msr->data = kvm_get_arch_capabilities();
+		msr->data = kvm_caps.supported_arch_cap;
 		break;
 	case MSR_IA32_PERF_CAPABILITIES:
 		msr->data = kvm_caps.supported_perf_cap;
@@ -9523,6 +9523,7 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 		kvm_caps.max_guest_tsc_khz = max;
 	}
 	kvm_caps.default_tsc_scaling_ratio = 1ULL << kvm_caps.tsc_scaling_ratio_frac_bits;
+	kvm_caps.supported_arch_cap = kvm_get_arch_capabilities();
 	kvm_init_msr_lists();
 	return 0;
 
@@ -11879,7 +11880,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	if (r)
 		goto free_guest_fpu;
 
-	vcpu->arch.arch_capabilities = kvm_get_arch_capabilities();
+	vcpu->arch.arch_capabilities = kvm_caps.supported_arch_cap;
 	vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
 	kvm_xen_init_vcpu(vcpu);
 	kvm_vcpu_mtrr_init(vcpu);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index c544602d07a3..d3e524bcc169 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -29,6 +29,7 @@ struct kvm_caps {
 	u64 supported_xcr0;
 	u64 supported_xss;
 	u64 supported_perf_cap;
+	u64 supported_arch_cap;
 };
 
 void kvm_spurious_fault(void);

base-commit: b3c98052d46948a8d65d2778c7f306ff38366aac
-- 
2.40.0