Re: [PATCH v1 4/4] KVM: x86: Advertise support for the immediate form of MSR instructions

[Sean Christopherson <seanjc@google.com>]

On Wed, Jul 30, 2025, Xin Li (Intel) wrote:
> Advertise support for the immediate form of MSR instructions to userspace
> if the instructions are supported by the underlying CPU.

SVM needs to explicitly clear the capability so that KVM doesn't over-advertise
support if AMD ever implements X86_FEATURE_MSR_IMM.

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ca550c4fa174..7e7821ee8ee1 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5311,8 +5311,12 @@ static __init void svm_set_cpu_caps(void)
        /* CPUID 0x8000001F (SME/SEV features) */
        sev_set_cpu_caps();
 
-       /* Don't advertise Bus Lock Detect to guest if SVM support is absent */
+       /*
+        * Clear capabilities that are automatically configured by common code,
+        * but that require explicit SVM support (that isn't yet implemented).
+        */
        kvm_cpu_cap_clear(X86_FEATURE_BUS_LOCK_DETECT);
+       kvm_cpu_cap_clear(X86_FEATURE_MSR_IMM);
 }
 
 static __init int svm_hardware_setup(void)