Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.35 as permitted sender) client-ip=23.128.96.35;
Message-ID: <7c7238a9c8b0dc6bc865407ba804a651cdfdb044.camel@infradead.org>
Subject: Re: [PATCH v8 15/15] KVM: xen: allow vcpu_info content to be
 'safely' copied
From:   David Woodhouse <dwmw2@infradead.org>
To:     Paul Durrant <paul@xen.org>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Wed, 22 Nov 2023 10:39:04 +0000
In-Reply-To: <4a76b7dc9055485d9e2592b395e60221dc349abf.camel@infradead.org>
References: <20231121180223.12484-1-paul@xen.org>
         <20231121180223.12484-16-paul@xen.org>
         <4a76b7dc9055485d9e2592b395e60221dc349abf.camel@infradead.org>
Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature";
        boundary="=-w8rojJzgTDFFtPqbqbDH"
User-Agent: Evolution 3.44.4-0ubuntu2 
MIME-Version: 1.0
Precedence: bulk


--=-w8rojJzgTDFFtPqbqbDH
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Tue, 2023-11-21 at 22:53 +0000, David Woodhouse wrote:
> On Tue, 2023-11-21 at 18:02 +0000, Paul Durrant wrote:
> > From: Paul Durrant <pdurrant@amazon.com>
> >=20
> > If the guest sets an explicit vcpu_info GPA then, for any of the first =
32
> > vCPUs, the content of the default vcpu_info in the shared_info page mus=
t be
> > copied into the new location. Because this copy may race with event
> > delivery (which updates the 'evtchn_pending_sel' field in vcpu_info) th=
ere
> > needs to be a way to defer that until the copy is complete.
> > Happily there is already a shadow of 'evtchn_pending_sel' in kvm_vcpu_x=
en
> > that is used in atomic context if the vcpu_info PFN cache has been
> > invalidated so that the update of vcpu_info can be deferred until the
> > cache can be refreshed (on vCPU thread's the way back into guest contex=
t).
> >=20
> > Also use this shadow if the vcpu_info cache has been *deactivated*, so =
that
> > the VMM can safely copy the vcpu_info content and then re-activate the
> > cache with the new GPA. To do this, stop considering an inactive vcpu_i=
nfo
> > cache as a hard error in kvm_xen_set_evtchn_fast().
> >=20
> > Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> > Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
>=20
> Wait, didn't we realise that this leaves the bits set in the shadow
> evtchn_pending_sel that get lost on migration?
>=20
> The point in your previous patch which split out a shiny new
> set_shinfo_evtchn_pending() function was that you could then *call*
> that function to ensure that the corresponding index bit was set on the
> destination host after migration, if the bit in the shinfo is.
>=20
> So we'd do that from kvm_xen_setup_evtchn(), kvm_xen_eventfd_assign(),
> and when setting KVM_XEN_VCPU_ATTR_TYPE_TIMER.
>=20
> =C2=A0if (bit_is_set_in_shinfo)
> =C2=A0=C2=A0 set_shinfo_evtchn_pending()

I mean set_vcpu_info_evtchn_pending() of course. And we probably want
to extend the xen_shinfo_test to test it, by setting the bit in the
shinfo to mark the event as pending, and then doing each of

 =E2=80=A2 Set up timer (a bit like in TEST_TIMER_RESTORE at line 817).
 =E2=80=A2 Add incoming eventfd with KVM_SET_GSI_ROUTING (cf. line 563)
 =E2=80=A2 Add IPI with KVM_XEN_ATTR_TYPE_EVTCHN (cf. line 597)

Each of those should set the index bit in the vcpu_info immediately if
the evtchn port is already set (and unmasked) in the shinfo.


(Ignore this part if you're cleverer than me or have had more coffee=E2=80=
=A6)

It took me a moment to get my head around the different setups we have
for event channels, but that's because the standard KVM_SET_GSI_ROUTING
one is for *incoming* events, just as we would for MSIs, and we use the
standard way of attaching an eventfd to an incoming GSI/MSI/evtchn.

The KVM_XEN_ATTR_TYPE_EVTCHN one is for *outbound* events where the
guest does an EVTCHNOP_send. That can *raise* events on an eventfd, or
it can be an IPI or loopback interdomain port, which is the case we
need to test.

--=-w8rojJzgTDFFtPqbqbDH
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Disposition: attachment; filename="smime.p7s"
Content-Transfer-Encoding: base64
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--=-w8rojJzgTDFFtPqbqbDH--