linux-kernel - Re: [PATCH v2 06/10] KVM: VMX: Don't invalidate hv_tlb

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Message-ID: <87tuun4roa.fsf@vitty.brq.redhat.com>
Date:   Wed, 21 Oct 2020 15:47:17 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/10] KVM: VMX: Don't invalidate hv_tlb_eptp if the new EPTP matches

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Don't invalidate the common EPTP, and thus trigger rechecking of EPTPs
> across all vCPUs, if the new EPTP matches the old/common EPTP.  In all
> likelihood this is a meaningless optimization, but there are (uncommon)
> scenarios where KVM can reload the same EPTP.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 4dfde8b64750..e6569bafacdc 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3043,7 +3043,8 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd,
>  		if (kvm_x86_ops.tlb_remote_flush) {
>  			spin_lock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>  			to_vmx(vcpu)->ept_pointer = eptp;
> -			to_kvm_vmx(kvm)->hv_tlb_eptp = INVALID_PAGE;
> +			if (eptp != to_kvm_vmx(kvm)->hv_tlb_eptp)
> +				to_kvm_vmx(kvm)->hv_tlb_eptp = INVALID_PAGE;
>  			spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>  		}

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly