linux-kernel - Re: [PATCH v2 23/32] KVM: nVMX: Add helper to handle TLB flushes on nested VM-Enter/VM-Exit

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Date:   Tue, 17 Mar 2020 18:17:59 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...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, Ben Gardon <bgardon@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Liran Alon <liran.alon@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        John Haxby <john.haxby@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v2 23/32] KVM: nVMX: Add helper to handle TLB flushes on
 nested VM-Enter/VM-Exit

On 17/03/20 05:52, Sean Christopherson wrote:
> +	nested_vmx_transition_tlb_flush(vcpu, vmcs12);
> +
> +	/*
> +	 * There is no direct mapping between vpid02 and vpid12, vpid02 is
> +	 * per-vCPU and reused for all nested vCPUs.  If vpid12 is changing
> +	 * then the new "virtual" VPID will reuse the same "real" VPID,
> +	 * vpid02, and so needs to be sync'd.  Skip the sync if a TLB flush
> +	 * has already been requested, but always update the last used VPID.
> +	 */
> +	if (nested_cpu_has_vpid(vmcs12) && nested_has_guest_tlb_tag(vcpu) &&
> +	    vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
> +		vmx->nested.last_vpid = vmcs12->virtual_processor_id;
> +		if (!kvm_test_request(KVM_REQ_TLB_FLUSH, vcpu))
> +			vpid_sync_context(nested_get_vpid02(vcpu));
>  	}

Would it make sense to move nested_vmx_transition_tlb_flush into an
"else" branch?  And should this also test that KVM_REQ_TLB_FLUSH_CURRENT
is not set?

Paolo