linux-kernel - [PATCH V2 4/5] KVM: SVM: Recalc instructions intercepts when EFER.SVME is toggled

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Message-ID: <20260112174535.3132800-5-chengkev@google.com>
Date: Mon, 12 Jan 2026 17:45:34 +0000
From: Kevin Cheng <chengkev@...gle.com>
To: seanjc@...gle.com, pbonzini@...hat.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, yosry.ahmed@...ux.dev, 
	Kevin Cheng <chengkev@...gle.com>
Subject: [PATCH V2 4/5] KVM: SVM: Recalc instructions intercepts when
 EFER.SVME is toggled

The AMD APM states that VMRUN, VMLOAD, VMSAVE, CLGI, VMMCALL, and
INVLPGA instructions should generate a #UD when EFER.SVME is cleared.
Currently, when VMLOAD, VMSAVE, or CLGI are executed in L1 with
EFER.SVME cleared, no #UD is generated in certain cases. This is because
the intercepts for these instructions are cleared based on whether or
not vls or vgif is enabled. The #UD fails to be generated when the
intercepts are absent.

Fix the missing #UD generation by ensuring that all relevant
instructions have intercepts set when SVME.EFER is disabled.

VMMCALL is special because KVM's ABI is that VMCALL/VMMCALL are always
supported for L1 and never fault.

Signed-off-by: Kevin Cheng <chengkev@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 92a2faff1ccc8..92a66b62cfabd 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -243,6 +243,8 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 			if (svm_gp_erratum_intercept && !sev_guest(vcpu->kvm))
 				set_exception_intercept(svm, GP_VECTOR);
 		}
+
+		kvm_make_request(KVM_REQ_RECALC_INTERCEPTS, vcpu);
 	}
 
 	svm->vmcb->save.efer = efer | EFER_SVME;
@@ -976,6 +978,7 @@ void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu)
 static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+	u64 efer = vcpu->arch.efer;
 
 	/*
 	 * Intercept INVPCID if shadow paging is enabled to sync/free shadow
@@ -996,7 +999,13 @@ static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu)
 			svm_set_intercept(svm, INTERCEPT_RDTSCP);
 	}
 
-	if (guest_cpuid_is_intel_compatible(vcpu)) {
+	/*
+	 * Intercept instructions that #UD if EFER.SVME=0, as SVME must be set even
+	 * when running the guest, i.e. hardware will only ever see EFER.SVME=1.
+	 */
+	if (guest_cpuid_is_intel_compatible(vcpu) || !(efer & EFER_SVME)) {
+		svm_set_intercept(svm, INTERCEPT_CLGI);
+		svm_set_intercept(svm, INTERCEPT_STGI);
 		svm_set_intercept(svm, INTERCEPT_VMLOAD);
 		svm_set_intercept(svm, INTERCEPT_VMSAVE);
 		svm->vmcb->control.virt_ext &= ~VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
-- 
2.52.0.457.g6b5491de43-goog