linux-kernel - Re: [PATCH v2] KVM: VMX: Set VMENTER_L1D_FLUSH_NOT_REQUIRED if !X86_BUG

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Message-ID: <d8dc9ae5-7a97-1aed-4c22-051587795789@redhat.com>
Date:   Fri, 27 Sep 2019 12:11:17 -0400
From:   Waiman Long <longman@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     bp@...en8.de
Subject: Re: [PATCH v2] KVM: VMX: Set VMENTER_L1D_FLUSH_NOT_REQUIRED if
 !X86_BUG_L1TF

On 9/27/19 12:05 PM, Paolo Bonzini wrote:
> From: Waiman Long <longman@...hat.com>
>
> The l1tf_vmx_mitigation is only set to VMENTER_L1D_FLUSH_NOT_REQUIRED
> when the ARCH_CAPABILITIES MSR indicates that L1D flush is not required.
> However, if the CPU is not affected by L1TF, l1tf_vmx_mitigation will
> still be set to VMENTER_L1D_FLUSH_AUTO. This is certainly not the best
> option for a !X86_BUG_L1TF CPU.
>
> So force l1tf_vmx_mitigation to VMENTER_L1D_FLUSH_NOT_REQUIRED to make it
> more explicit in case users are checking the vmentry_l1d_flush parameter.
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> [Patch rewritten accoring to Borislav Petkov's suggestion. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index d4575ffb3cec..e7970a2e8eae 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -209,6 +209,11 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
>  	struct page *page;
>  	unsigned int i;
>  
> +	if (!boot_cpu_has_bug(X86_BUG_L1TF)) {
> +		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
> +		return 0;
> +	}
> +
>  	if (!enable_ept) {
>  		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_EPT_DISABLED;
>  		return 0;
> @@ -7995,12 +8000,10 @@ static int __init vmx_init(void)
>  	 * contain 'auto' which will be turned into the default 'cond'
>  	 * mitigation mode.
>  	 */
> -	if (boot_cpu_has(X86_BUG_L1TF)) {
> -		r = vmx_setup_l1d_flush(vmentry_l1d_flush_param);
> -		if (r) {
> -			vmx_exit();
> -			return r;
> -		}
> +	r = vmx_setup_l1d_flush(vmentry_l1d_flush_param);
> +	if (r) {
> +		vmx_exit();
> +		return r;
>  	}
>  
>  #ifdef CONFIG_KEXEC_CORE

That looks cleaner. Thanks for the suggestion and rewrite.

Cheers,
Longman