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KVM: SVM: Disable interception of SPEC_CTRL iff the MSR exists for the guest

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Disable interception of SPEC_CTRL when the CPU virtualizes (i.e. context
switches) SPEC_CTRL if and only if the MSR exists according to the vCPU's
CPUID model.  Letting the guest access SPEC_CTRL is generally benign, but
the guest would see inconsistent behavior if KVM happened to emulate an
access to the MSR.

Fixes: d00b99c514 ("KVM: SVM: Add support for Virtual SPEC_CTRL")
Reported-by: Chao Gao <chao.gao@intel.com>
Link: https://lore.kernel.org/r/20250610225737.156318-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2025-06-10 15:57:06 -07:00
parent 6b1dd26544
commit 674ffc6503
1 changed files with 6 additions and 3 deletions
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9
arch/x86/kvm/svm/svm.c
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@@ -1356,11 +1356,14 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
svm_recalc_instruction_intercepts(vcpu, svm);
/*
* If the host supports V_SPEC_CTRL then disable the interception
* of MSR_IA32_SPEC_CTRL.
* If the CPU virtualizes MSR_IA32_SPEC_CTRL, i.e. KVM doesn't need to
* manually context switch the MSR, immediately configure interception
* of SPEC_CTRL, without waiting for the guest to access the MSR.
*/
if (boot_cpu_has(X86_FEATURE_V_SPEC_CTRL))
set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SPEC_CTRL, 1, 1);
set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SPEC_CTRL,
guest_has_spec_ctrl_msr(vcpu),
guest_has_spec_ctrl_msr(vcpu));
if (kvm_vcpu_apicv_active(vcpu))
avic_init_vmcb(svm, vmcb);