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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.11.16 at 15:37, <boris.ostrovsky@xxxxxxxxxx> wrote:

> 
> On 11/22/2016 08:59 AM, Jan Beulich wrote:
>>>>> On 22.11.16 at 13:34, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>
>>>
>>> On 11/22/2016 05:39 AM, Jan Beulich wrote:
>>>>>>> On 22.11.16 at 11:31, <JBeulich@xxxxxxxx> wrote:
>>>>>>>> On 21.11.16 at 22:00, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>>>> This domctl is called when a VCPU is hot-(un)plugged to a guest (via
>>>>>> 'xl vcpu-set').
>>>>>>
>>>>>> The primary reason for adding this call is because for PVH guests
>>>>>> the hypervisor needs to send an SCI and set GPE registers. This is
>>>>>> unlike HVM guests that have qemu to perform these tasks.
>>>>>
>>>>> And the tool stack can't do this?
>>>>
>>>> For the avoidance of further misunderstandings: Of course likely
>>>> not completely on its own, but by using a (to be introduced) more
>>>> low level hypervisor interface (setting arbitrary GPE bits, with SCI
>>>> raised as needed, or the SCI raising being another hypercall).
>>>
>>> So you are suggesting breaking up XEN_DOMCTL_set_avail_vcpus into
>>>
>>> XEN_DOMCTL_set_acpi_reg(io_offset, length, val)
>>> XEN_DOMCTL_set_avail_vcpus(avail_vcpus_bitmap)
>>> XEN_DOMCTL_send_virq(virq)
>>>
>>> (with perhaps set_avail_vcpus folded into set_acpi_reg) ?
>>
>> Well, I don't see what set_avail_vcpus would be good for
>> considering that during v2 review you've said that you need it
>> just for the GPE modification and SCI sending.
> 
> 
> Someone needs to provide the hypervisor with the new number of available 
> (i.e. hot-plugged/unplugged) VCPUs, thus the name of the domctl. GPE/SCI 
> manipulation are part of that update.
> 
> (I didn't say it during v2 review and I should have)

And I've just found that need while looking over patch 8. With
that I'm not sure the splitting would make sense, albeit we may
find it necessary to fiddle with other GPE bits down the road.

Jan


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