Re: [Xen-devel] [PATCH v3 01/11] x86/domctl: Add XEN_DOMCTL_set_avail_vcpus

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.11.16 at 00:47, <boris.ostrovsky@xxxxxxxxxx> wrote:
> I have a prototype that replaces XEN_DOMCTL_set_avail_vcpus with 
> XEN_DOMCTL_acpi_access and it seems to work OK. The toolstack needs to 
> perform two (or more, if >32 VCPUs) hypercalls and the logic on the 
> hypervisor side is almost the same as the ioreq handling that this 
> series added in patch 8.

Why would there be multiple hypercalls needed? (I guess I may need
to see the prototype to understand.)

> However, I now realized that this interface will not be available to PV 
> guests (and it will only become available to HVM guests when we move 
> hotplug from qemu to hypervisor). And it's x86-specific.

As you make clear below, the PV aspect is likely a non-issue. But
why is this x86-specific? It's generic ACPI, isn't it?

Jan

> This means that PV guests will not know what the number of available 
> VCPUs is and therefore we will not be able to enforce it. OTOH we don't 
> know how to do that anyway since PV guests bring up all VCPUs and then 
> offline them.
> 
> -boris




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