KVM: SVM: Pass through shadow stack MSRs as appropriate

Pass through XSAVE managed CET MSRs on SVM when KVM supports shadow
stack. These cannot be intercepted without also intercepting XSAVE which
would likely cause unacceptable performance overhead.
MSR_IA32_INT_SSP_TAB is not managed by XSAVE, so it is intercepted.

Reviewed-by: Chao Gao <[email protected]>
Signed-off-by: John Allen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: jallen-amd

arch/x86/kvm/svm/svm.c

@@ -844,6 +844,17 @@ static void svm_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
 		svm_disable_intercept_for_msr(vcpu, MSR_IA32_MPERF, MSR_TYPE_R);
 	}
 
+	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
+		bool shstk_enabled = guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
+
+		svm_set_intercept_for_msr(vcpu, MSR_IA32_U_CET, MSR_TYPE_RW, !shstk_enabled);
+		svm_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, !shstk_enabled);
+		svm_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP, MSR_TYPE_RW, !shstk_enabled);
+		svm_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP, MSR_TYPE_RW, !shstk_enabled);
+		svm_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP, MSR_TYPE_RW, !shstk_enabled);
+		svm_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP, MSR_TYPE_RW, !shstk_enabled);
+	}
+
 	if (sev_es_guest(vcpu->kvm))
 		sev_es_recalc_msr_intercepts(vcpu);