linux-kernel - [PATCH v15 28/41] KVM: x86: SVM: Pass through shadow stack MSRs as appropriate

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Message-ID: <20250912232319.429659-29-seanjc@google.com>
Date: Fri, 12 Sep 2025 16:23:06 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Mathias Krause <minipli@...ecurity.net>, 
	John Allen <john.allen@....com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Chao Gao <chao.gao@...el.com>, Maxim Levitsky <mlevitsk@...hat.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: [PATCH v15 28/41] KVM: x86: SVM: Pass through shadow stack MSRs as appropriate

From: John Allen <john.allen@....com>

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@...el.com>
Signed-off-by: John Allen <john.allen@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 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 c0a16481b9c3..dc4d34e6af33 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);
 
-- 
2.51.0.384.g4c02a37b29-goog