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: <052867ae1c997487d85c21e995feb5647ac6c458.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>,
        Ankur Arora <ankur.a.arora@oracle.com>
Cc:     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,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 02 Dec 2020 19:02:33 +0000
In-Reply-To: <c43024b3-6508-3b77-870c-da81e74284a4@oracle.com>
References: <20190220201609.28290-1-joao.m.martins@oracle.com>
         <20190220201609.28290-11-joao.m.martins@oracle.com>
         <71753a370cd6f9dd147427634284073b78679fa6.camel@infradead.org>
         <53baeaa7-0fed-d22c-7767-09ae885d13a0@oracle.com>
         <4ad0d157c5c7317a660cd8d65b535d3232f9249d.camel@infradead.org>
         <c43024b3-6508-3b77-870c-da81e74284a4@oracle.com>
Content-Type: multipart/signed; micalg="sha-256";
        protocol="application/x-pkcs7-signature";
        boundary="=-VwpSknYF+oE4Vdku3Yf5"
Mime-Version: 1.0
Precedence: bulk


--=-VwpSknYF+oE4Vdku3Yf5
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, 2020-12-02 at 18:34 +0000, Joao Martins wrote:
> On 12/2/20 4:47 PM, David Woodhouse wrote:
> > On Wed, 2020-12-02 at 13:12 +0000, Joao Martins wrote:
> > > On 12/2/20 11:17 AM, David Woodhouse wrote:
> > > > 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 routi=
ng
> > > > table is { vcpu, port# } which get passed to kvm_xen_evtchn_send().
> > >=20
> > > But passing port to the routing and handling the sending of events wo=
uldn't it lead to
> > > unnecessary handling of event channels which aren't handled by the ke=
rnel, compared to
> > > just injecting caring about the upcall?
> >=20
> > Well, I'm generally in favour of *not* doing things in the kernel that
> > don't need to be there.
> >=20
> > But if the kernel is going to short-circuit the IPIs and VIRQs, then
> > it's already going to have to handle the evtchn_pending/evtchn_mask
> > bitmaps, and actually injecting interrupts.
> >=20
>=20
> Right. I was trying to point that out in the discussion we had
> in next patch. But true be told, more about touting the idea of kernel
> knowing if a given event channel is registered for userspace handling,
> rather than fully handling the event channel.
>=20
> I suppose we are able to provide both options to the VMM anyway
> i.e. 1) letting them handle it enterily in userspace by intercepting
> EVTCHNOP_send, or through the irq route if we want kernel to offload it.

Right. The kernel takes what it knows about and anything else goes up
to userspace.

I do like the way you've handled the vcpu binding in userspace, and the
kernel just knows that a given port goes to a given target CPU.

>=20
> > For the VMM
> > API I think we should follow the Xen model, mixing the domain-wide and
> > per-vCPU configuration. It's the best way to faithfully model the
> > behaviour a true Xen guest would experience.
> >=20
> > So KVM_XEN_ATTR_TYPE_CALLBACK_VIA can be used to set one of
> >  =E2=80=A2 HVMIRQ_callback_vector, taking a vector#
> >  =E2=80=A2 HVMIRQ_callback_gsi for the in-kernel irqchip, taking a GSI#
> >=20
> > And *maybe* in a later patch it could also handle
> >  =E2=80=A2 HVMIRQ_callback_gsi for split-irqchip, taking an eventfd
> >  =E2=80=A2 HVMIRQ_callback_pci_intx, taking an eventfd (or a pair, for =
EOI?)
> >=20
>=20
> Most of the Xen versions we were caring had callback_vector and
> vcpu callback vector (despite Linux not using the latter). But if you're
> dating back to 3.2 and 4.1 well (or certain Windows drivers), I suppose
> gsi and pci-intx are must-haves.

Note sure about GSI but PCI-INTX is definitely something I've seen in
active use by customers recently. I think SLES10 will use that.

> I feel we could just accommodate it as subtype in KVM_XEN_ATTR_TYPE_CALLB=
ACK_VIA.
> Don't see the adavantage in having another xen attr type.

Yeah, fair enough.

> But kinda have mixed feelings in having kernel handling all event channel=
s ABI,
> as opposed to only the ones userspace asked to offload. It looks a tad un=
ncessary besides
> the added gain to VMMs that don't need to care about how the internals of=
 event channels.
> But performance-wise it wouldn't bring anything better. But maybe, the fo=
rmer is reason
> enough to consider it.

Yeah, we'll see. Especially when it comes to implementing FIFO event
channels, I'd rather just do it in one place =E2=80=94 and if the kernel do=
es
it anyway then it's hardly difficult to hook into that.

But I've been about as coherent as I can be in email, and I think we're
generally aligned on the direction. I'll do some more experiments and
see what I can get working, and what it looks like.

I'm focusing on making the shinfo stuff all use kvm_map_gfn() first.

--=-VwpSknYF+oE4Vdku3Yf5
Content-Type: application/x-pkcs7-signature; name="smime.p7s"
Content-Disposition: attachment; filename="smime.p7s"
Content-Transfer-Encoding: base64
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--=-VwpSknYF+oE4Vdku3Yf5--