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

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

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));


Julien Grall

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