Re: [PATCH v4 6/6] KVM: VMX: Move VERW closer to VMentry for MDS mitigation

[Josh Poimboeuf]

On Fri, Oct 27, 2023 at 07:39:12AM -0700, Pawan Gupta wrote:
> -	vmx_disable_fb_clear(vmx);
> +	/*
> +	 * Optimize the latency of VERW in guests for MMIO mitigation. Skip
> +	 * the optimization when MDS mitigation(later in asm) is enabled.
> +	 */
> +	if (!cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF))
> +		vmx_disable_fb_clear(vmx);
>  
>  	if (vcpu->arch.cr2 != native_read_cr2())
>  		native_write_cr2(vcpu->arch.cr2);
> @@ -7248,7 +7256,8 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
>  
>  	vmx->idt_vectoring_info = 0;
>  
> -	vmx_enable_fb_clear(vmx);
> +	if (!cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF))
> +		vmx_enable_fb_clear(vmx);
>  

It may be cleaner to instead check X86_FEATURE_CLEAR_CPU_BUF when
setting vmx->disable_fb_clear in the first place, in
vmx_update_fb_clear_dis().

-- 
Josh