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Re: [libvirt] [PATCH 3/5] qemu: Use GICv2 for aarch64/virt TCG guests



On Mon, 2017-05-15 at 12:53 +0200, Peter Krempa wrote:
> > +        /* We want to use the highest available GIC version for guests;
> > +         * however, the emulated GICv3 is currently lacking a MSI controller,
> > +         * making it unsuitable for the pure PCIe topology we aim for.
> > +         *
> > +         * For that reason, we skip this step entirely for TCG guests,
> > +         * and rely on the code below to pick the default version, GICv2,
> > +         * which supports all the features we need.
> > +         *
> > +         * We'll want to revisit this once MSI support for GICv3 has been
> > +         * implemented in QEMU.
> > +         *
> > +         * See https://bugzilla.redhat.com/show_bug.cgi?id=1414081 */
> > +        if (def->virtType == VIR_DOMAIN_VIRT_KVM) {
> 
> Currently it does not matter that much, since there are only two
> versions but this looks very non-future-proof to me.
> 
> When qemu adds the feature you'll need to add a capability, where you
> also enable the code below for TCG guests.
> 
> If there will be another version or something the condition will need to
> be altered.
> 
> I'd rather see that v3 is specifically disqualified for TCG guests
> (which will be later relaxed using the capability.). That way you'll
> still run the detection process.

Can do.

I'll post a respin shortly.

-- 
Andrea Bolognani / Red Hat / Virtualization


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