linux-kernel - [PATCH 3/6] KVM: SVM: Passthrough MSR_IA32_PRED

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Message-ID: <20230322011440.2195485-4-seanjc@google.com>
Date:   Tue, 21 Mar 2023 18:14:37 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Emanuele Giuseppe Esposito <eesposit@...hat.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: [PATCH 3/6] KVM: SVM: Passthrough MSR_IA32_PRED_CMD based purely on
 host+guest CPUID

Passthrough MSR_IA32_PRED_CMD based purely on whether or not the MSR is
supported and enabled, i.e. don't wait until the first write.  There's no
benefit to deferred passthrough, and the extra logic only adds complexity.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 252e7f37e4e2..f757b436ffae 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2955,7 +2955,6 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 			break;
 
 		wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
-		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PRED_CMD, 0, 1);
 		break;
 	case MSR_AMD64_VIRT_SPEC_CTRL:
 		if (!msr->host_initiated &&
@@ -4151,6 +4150,10 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 
 	svm_recalc_instruction_intercepts(vcpu, svm);
 
+	if (boot_cpu_has(X86_FEATURE_IBPB))
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PRED_CMD, 0,
+				     !!guest_has_pred_cmd_msr(vcpu));
+
 	/* For sev guests, the memory encryption bit is not reserved in CR3.  */
 	if (sev_guest(vcpu->kvm)) {
 		best = kvm_find_cpuid_entry(vcpu, 0x8000001F);
-- 
2.40.0.rc2.332.ga46443480c-goog