Re: [Xen-devel] [PATCH V2 1/8] xen/arm64: increase MAX_VIRT_CPUS to 128 on arm64

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Chen,

On 25/05/2015 03:01, Chen Baozi wrote:
> On Sat, May 23, 2015 at 03:46:32PM +0100, Julien Grall wrote:
> > On 23/05/2015 14:52, Chen Baozi wrote:
> > > From: Chen Baozi <baozich@xxxxxxxxx>
> > >
> > > GIC-500 supports up to 128 cores in a single SoC. Increase MAX_VIRT_CPUS
> > > to 128 on arm64.
> > This series have to be bisectable. Although, this patch will break
> > compilation on ARM64 because you increased MAX_VIRT_CPUS without the
> > re-distributor region (done in the next patch).
> >
> > Furthermore, GICv2 is only supporting 8 CPUs. We don't have to allow a guest
> > with more than 8 vCPUs when the GICv2 is in use.
> What's your suggestion? I don't think we could know whether it is built for
> a GICv2 or a GICv3 machine and define different values for corresponding
> target.
I'm not sure to understand your problem here. You know which vGIC 
version is emulated for a specific domain at domain creation time. The 
function domain_max_vcpus returns the maximum vCPUs for a give domain.
You could create a new field in vgic_v2_ops to store the maximum number 
of vCPU handled.
domain_max_vcpus would look like:

return (min(d->arch->vgic.handler.max_vcpus, MAX_VIRT_CPUS));

Regards,

--
--
Julien Grall

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