Re: [PATCH v3 3/4] KVM: SVM: Don't advertise Bus Lock Detect to guest if SVM support is missing

[Tom Lendacky <thomas.lendacky@amd.com>]

On 8/6/24 07:54, Ravi Bangoria wrote:
> 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: 76ea438b4afc ("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>

> ---
>  arch/x86/kvm/svm/svm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index c115d26844f7..85631112c872 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -5223,6 +5223,9 @@ 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)