[PATCH v4 3/5] KVM: x86: SVM: Pass through shadow stack MSRs

[John Allen]

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 <chao.gao@xxxxxxxxx>
Signed-off-by: John Allen <john.allen@xxxxxxx>
---
v4:
  - Don't pass through MSR_IA32_INT_SSP_TAB
---
 arch/x86/kvm/svm/svm.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index aee1bb8c01d0..b18573b530aa 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/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);
 
-- 
2.47.3