linux-kernel - Re: [PATCH v2 05/10] KVM: VMX: Invalidate hv_tlb

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Date:   Wed, 21 Oct 2020 14:39:20 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.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 05/10] KVM: VMX: Invalidate hv_tlb_eptp to denote an EPTP mismatch

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

> Drop the dedicated 'ept_pointers_match' field in favor of stuffing
> 'hv_tlb_eptp' with INVALID_PAGE to mark it as invalid, i.e. to denote
> that there is at least one EPTP mismatch.  Use a local variable to
> track whether or not a mismatch is detected so that hv_tlb_eptp can be
> used to skip redundant flushes.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 16 ++++++++--------
>  arch/x86/kvm/vmx/vmx.h |  7 -------
>  2 files changed, 8 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 52cb9eec1db3..4dfde8b64750 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -498,13 +498,13 @@ static int hv_remote_flush_tlb_with_range(struct kvm *kvm,
>  	struct kvm_vmx *kvm_vmx = to_kvm_vmx(kvm);
>  	struct kvm_vcpu *vcpu;
>  	int ret = 0, i;
> +	bool mismatch;
>  	u64 tmp_eptp;
>  
>  	spin_lock(&kvm_vmx->ept_pointer_lock);
>  
> -	if (kvm_vmx->ept_pointers_match != EPT_POINTERS_MATCH) {
> -		kvm_vmx->ept_pointers_match = EPT_POINTERS_MATCH;
> -		kvm_vmx->hv_tlb_eptp = INVALID_PAGE;
> +	if (!VALID_PAGE(kvm_vmx->hv_tlb_eptp)) {
> +		mismatch = false;
>  
>  		kvm_for_each_vcpu(i, vcpu, kvm) {
>  			tmp_eptp = to_vmx(vcpu)->ept_pointer;
> @@ -515,12 +515,13 @@ static int hv_remote_flush_tlb_with_range(struct kvm *kvm,
>  			if (!VALID_PAGE(kvm_vmx->hv_tlb_eptp))
>  				kvm_vmx->hv_tlb_eptp = tmp_eptp;
>  			else
> -				kvm_vmx->ept_pointers_match
> -					= EPT_POINTERS_MISMATCH;
> +				mismatch = true;
>  
>  			ret |= hv_remote_flush_eptp(tmp_eptp, range);
>  		}
> -	} else if (VALID_PAGE(kvm_vmx->hv_tlb_eptp)) {
> +		if (mismatch)
> +			kvm_vmx->hv_tlb_eptp = INVALID_PAGE;
> +	} else {
>  		ret = hv_remote_flush_eptp(kvm_vmx->hv_tlb_eptp, range);
>  	}

Personally, I find double negations like 'mismatch = false' hard to read
:-). What if we write this all like 

if (!VALID_PAGE(kvm_vmx->hv_tlb_eptp)) {
	kvm_vmx->hv_tlb_eptp = to_vmx(vcpu0)->ept_pointer;
	kvm_for_each_vcpu() {
		tmp_eptp = to_vmx(vcpu)->ept_pointer;
		if (!VALID_PAGE(tmp_eptp) || tmp_eptp != kvm_vmx->hv_tlb_eptp)
			kvm_vmx->hv_tlb_eptp = INVALID_PAGE;

		if (VALID_PAGE(tmp_eptp))
			ret |= hv_remote_flush_eptp(tmp_eptp, range);
	}
} else {
	ret = hv_remote_flush_eptp(kvm_vmx->hv_tlb_eptp, range);
}

(not tested and I've probably missed something)

>  
> @@ -3042,8 +3043,7 @@ 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)->ept_pointers_match
> -				= EPT_POINTERS_CHECK;
> +			to_kvm_vmx(kvm)->hv_tlb_eptp = INVALID_PAGE;
>  			spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>  		}
>  
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 3d557a065c01..e8d7d07b2020 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -288,12 +288,6 @@ struct vcpu_vmx {
>  	} shadow_msr_intercept;
>  };
>  
> -enum ept_pointers_status {
> -	EPT_POINTERS_CHECK = 0,
> -	EPT_POINTERS_MATCH = 1,
> -	EPT_POINTERS_MISMATCH = 2
> -};
> -
>  struct kvm_vmx {
>  	struct kvm kvm;
>  
> @@ -302,7 +296,6 @@ struct kvm_vmx {
>  	gpa_t ept_identity_map_addr;
>  
>  	hpa_t hv_tlb_eptp;
> -	enum ept_pointers_status ept_pointers_match;
>  	spinlock_t ept_pointer_lock;
>  };

-- 
Vitaly