KVM: SVM: Don't advertise Bus Lock Detect to guest if SVM support is missing

commit 54950bfe2b69cdc06ef753872b5225e54eb73506 upstream.

If host supports Bus Lock Detect, KVM advertises it to guests even if
SVM support is absent. Additionally, guest wouldn't be able to use it
despite guest CPUID bit being set. Fix it by unconditionally clearing
the feature bit in KVM cpu capability.

Reported-by: Jim Mattson <jmattson@google.com>
Closes: https://lore.kernel.org/r/CALMp9eRet6+v8Y1Q-i6mqPm4hUow_kJNhmVHfOV8tMfuSS=tVg@mail.gmail.com
Fixes: 76ea438b4a ("KVM: X86: Expose bus lock debug exception to guest")
Cc: stable@vger.kernel.org
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240808062937.1149-4-ravi.bangoria@amd.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/kvm/svm/svm.c

@@ -958,6 +958,9 @@ 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 */
+	kvm_cpu_cap_clear(X86_FEATURE_BUS_LOCK_DETECT);
 }
 
 static __init int svm_hardware_setup(void)