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

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Date:   Thu, 26 Sep 2019 13:29:28 -0400
From:   Waiman Long <longman@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: VMX: Set VMENTER_L1D_FLUSH_NOT_REQUIRED if
 !X86_BUG_L1TF

On 8/26/19 3:30 PM, Waiman Long wrote:
> 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>
> ---
>  arch/x86/kvm/vmx/vmx.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 42ed3faa6af8..a00ce3d6bbfd 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7896,6 +7896,8 @@ static int __init vmx_init(void)
>  			vmx_exit();
>  			return r;
>  		}
> +	} else {
> +		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
>  	}
>  
>  #ifdef CONFIG_KEXEC_CORE

Ping. Any comment on that one?

Cheers,
Longman