linux-kernel - Re: [PATCH v2 03/10] KVM: VMX: Fold Hyper-V EPTP checking into it's only caller

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Date:   Wed, 21 Oct 2020 14:08:29 +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 03/10] KVM: VMX: Fold Hyper-V EPTP checking into it's only caller

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

> Fold check_ept_pointer_match() into hv_remote_flush_tlb_with_range() in
> preparation for combining the kvm_for_each_vcpu loops of the ==CHECK and
> !=MATCH statements.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 42 +++++++++++++++++++-----------------------
>  1 file changed, 19 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 6d41c99c70c4..bba6d91f1fe1 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -469,27 +469,6 @@ static const u32 vmx_uret_msrs_list[] = {
>  static bool __read_mostly enlightened_vmcs = true;
>  module_param(enlightened_vmcs, bool, 0444);
>  
> -/* check_ept_pointer() should be under protection of ept_pointer_lock. */
> -static void check_ept_pointer_match(struct kvm *kvm)
> -{
> -	struct kvm_vcpu *vcpu;
> -	u64 tmp_eptp = INVALID_PAGE;
> -	int i;
> -
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (!VALID_PAGE(tmp_eptp)) {
> -			tmp_eptp = to_vmx(vcpu)->ept_pointer;
> -		} else if (tmp_eptp != to_vmx(vcpu)->ept_pointer) {
> -			to_kvm_vmx(kvm)->ept_pointers_match
> -				= EPT_POINTERS_MISMATCH;
> -			return;
> -		}
> -	}
> -
> -	to_kvm_vmx(kvm)->hv_tlb_eptp = tmp_eptp;
> -	to_kvm_vmx(kvm)->ept_pointers_match = EPT_POINTERS_MATCH;
> -}
> -
>  static int kvm_fill_hv_flush_list_func(struct hv_guest_mapping_flush_list *flush,
>  		void *data)
>  {
> @@ -519,11 +498,28 @@ 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;
> +	u64 tmp_eptp;
>  
>  	spin_lock(&kvm_vmx->ept_pointer_lock);
>  
> -	if (kvm_vmx->ept_pointers_match == EPT_POINTERS_CHECK)
> -		check_ept_pointer_match(kvm);
> +	if (kvm_vmx->ept_pointers_match == EPT_POINTERS_CHECK) {
> +		kvm_vmx->ept_pointers_match = EPT_POINTERS_MATCH;
> +		kvm_vmx->hv_tlb_eptp = INVALID_PAGE;
> +
> +		kvm_for_each_vcpu(i, vcpu, kvm) {
> +			tmp_eptp = to_vmx(vcpu)->ept_pointer;
> +			if (!VALID_PAGE(tmp_eptp))
> +				continue;
> +
> +			if (!VALID_PAGE(kvm_vmx->hv_tlb_eptp)) {
> +				kvm_vmx->hv_tlb_eptp = tmp_eptp;
> +			} else if (kvm_vmx->hv_tlb_eptp != tmp_eptp) {
> +				kvm_vmx->ept_pointers_match
> +					= EPT_POINTERS_MISMATCH;
> +				break;

Actually no (scratch my comment on PATCH1), in case pointers differ
kvm_vmx->hv_tlb_eptp remains set to the last matched EPTP. This likely
doesn't matter as we're not going to use it but maybe sacrificing couple
instructions and resetting it here to INVALID_PAGE (or actually setting
it only in case of EPT_POINTERS_MATCH after the loop)?

> +			}
> +		}
> +	}
>  
>  	if (kvm_vmx->ept_pointers_match != EPT_POINTERS_MATCH) {
>  		kvm_for_each_vcpu(i, vcpu, kvm) {

-- 
Vitaly