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

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 <[email protected]>
Closes: https://lore.kernel.org/r/CALMp9eRet6+v8Y1Q-i6mqPm4hUow_kJNhmVHfOV8tMfuSS=tVg@mail.gmail.com
Fixes: 76ea438 ("KVM: X86: Expose bus lock debug exception to guest")
Cc: [email protected]
Signed-off-by: Ravi Bangoria <[email protected]>
Reviewed-by: Jim Mattson <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: Ravi Bangoria

arch/x86/kvm/svm/svm.c

@@ -5236,6 +5236,9 @@ 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)