linux-kernel - Re: [PATCH v4 6/6] KVM: nVMX: Enable nested posted interrupt processing

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Date:	Mon, 02 Feb 2015 12:03:13 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wincy Van <fanwenyi0529@...il.com>,
	"gleb@...nel.org" <gleb@...nel.org>,
	"Zhang, Yang Z" <yang.z.zhang@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Jan Kiszka <jan.kiszka@....de>
Subject: Re: [PATCH v4 6/6] KVM: nVMX: Enable nested posted interrupt processing



On 28/01/2015 17:02, Wincy Van wrote:
> +static int vmx_deliver_nested_posted_interrupt(struct kvm_vcpu *vcpu,
> +                                               int vector)
> +{
> +       if (is_guest_mode(vcpu) &&
> +           vector == to_vmx(vcpu)->nested.posted_intr_nv &&
> +           vcpu->mode == IN_GUEST_MODE) {
> +               /* the PIR and ON have been set by L1. */

What happens if there is a L2->L0->L2 exit on the target VCPU, and the
guest exits before apic->send_IPI_mask sends the IPI?

The L1 hypervisor might "know" somehow that there cannot be a concurrent
L2->L1->L2 exit, and not do the equivalent of KVM's

        kvm_make_request(KVM_REQ_EVENT, vcpu);

after it sets ON.

So I think you have to do something like

static bool vmx_is_nested_posted_interrupt(struct kvm_vcpu *vcpu,
					   int vector)
{
	return (is_guest_mode(vcpu) &&
                vector == to_vmx(vcpu)->nested.posted_intr_nv);
}

and in vmx_deliver_posted_interrupt:

	r = 0;
	if (!vmx_is_nested_posted_interrupt(vcpu, vector)) {
	        if (pi_test_and_set_pir(vector, &vmx->pi_desc))
	                return;

	        r = pi_test_and_set_on(&vmx->pi_desc);
	}
        kvm_make_request(KVM_REQ_EVENT, vcpu);
#ifdef CONFIG_SMP
        if (!r && (vcpu->mode == IN_GUEST_MODE))
                apic->send_IPI_mask(get_cpu_mask(vcpu->cpu),
                                POSTED_INTR_VECTOR);
        else
#endif
                kvm_vcpu_kick(vcpu);


What do you think?

Paolo

> +               apic->send_IPI_mask(get_cpu_mask(vcpu->cpu),
> +                               POSTED_INTR_VECTOR);
> +               return 0;
> +       }
> +       return -1;
> +}
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