Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <71753a370cd6f9dd147427634284073b78679fa6.camel@infradead.org>
Subject: Re: [PATCH RFC 10/39] KVM: x86/xen: support upcall vector
From:   David Woodhouse <dwmw2@infradead.org>
To:     Joao Martins <joao.m.martins@oracle.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Ankur Arora <ankur.a.arora@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org
Date:   Wed, 02 Dec 2020 11:17:32 +0000
In-Reply-To: <20190220201609.28290-11-joao.m.martins@oracle.com>
References: <20190220201609.28290-1-joao.m.martins@oracle.com>
         <20190220201609.28290-11-joao.m.martins@oracle.com>
Content-Type: multipart/signed; micalg="sha-256";
        protocol="application/x-pkcs7-signature";
        boundary="=-pVlUDTxbpk4Ut313iSVZ"
Mime-Version: 1.0
Precedence: bulk


--=-pVlUDTxbpk4Ut313iSVZ
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, 2019-02-20 at 20:15 +0000, Joao Martins wrote:
> @@ -176,6 +177,9 @@ int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_r=
outing_entry *e,
>         int r;
> =20
>         switch (e->type) {
> +       case KVM_IRQ_ROUTING_XEN_EVTCHN:
> +               return kvm_xen_set_evtchn(e, kvm, irq_source_id, level,
> +                                      line_status);
>         case KVM_IRQ_ROUTING_HV_SINT:
>                 return kvm_hv_set_sint(e, kvm, irq_source_id, level,
>                                        line_status);
> @@ -325,6 +329,13 @@ int kvm_set_routing_entry(struct kvm *kvm,
>                 e->hv_sint.vcpu =3D ue->u.hv_sint.vcpu;
>                 e->hv_sint.sint =3D ue->u.hv_sint.sint;
>                 break;
> +       case KVM_IRQ_ROUTING_XEN_EVTCHN:
> +               e->set =3D kvm_xen_set_evtchn;
> +               e->evtchn.vcpu =3D ue->u.evtchn.vcpu;
> +               e->evtchn.vector =3D ue->u.evtchn.vector;
> +               e->evtchn.via =3D ue->u.evtchn.via;
> +
> +               return kvm_xen_setup_evtchn(kvm, e);
>         default:
>                 return -EINVAL;
>         }


Hmm. I'm not sure I've have done it that way.

These IRQ routing entries aren't for individual event channel ports;
they don't map to kvm_xen_evtchn_send().

They actually represent the upcall to the given vCPU when any event
channel is signalled, and it's really per-vCPU configuration.

When the kernel raises (IPI, VIRQ) events on a given CPU, it doesn't
actually use these routing entries; it just uses the values in
vcpu_xen->cb.{via,vector} which were cached from the last of these IRQ
routing entries that happens to have been processed?

The VMM is *expected* to set up precisely one of these for each vCPU,
right? Would it not be better to do that via KVM_XEN_HVM_SET_ATTR?

The usage model for userspace is presumably that the VMM should set the
appropriate bit in evtchn_pending, check evtchn_mask and then call into
the kernel to do the set_irq() to inject the callback vector to the
guest?

I might be more inclined to go for a model where the kernel handles the
evtchn_pending/evtchn_mask for us. What would go into the irq routing
table is { vcpu, port# } which get passed to kvm_xen_evtchn_send().

Does that seem reasonable?

Either way, I do think we need a way for events raised in the kernel to
be signalled to userspace, if they are targeted at a vCPU which has
CALLBACK_VIA_INTX that the kernel can't do directly. So we probably
*do* need that eventfd I was objecting to earlier, except that it's not
a per-evtchn thing; it's per-vCPU.


--=-pVlUDTxbpk4Ut313iSVZ
Content-Type: application/x-pkcs7-signature; name="smime.p7s"
Content-Disposition: attachment; filename="smime.p7s"
Content-Transfer-Encoding: base64
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--=-pVlUDTxbpk4Ut313iSVZ--