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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.11.16 at 16:43, <boris.ostrovsky@xxxxxxxxxx> wrote:

> 
> On 11/22/2016 10:07 AM, Jan Beulich wrote:
>>>>> 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.
> 
> Just to make sure we are talking about the same thing: 
> XEN_DOMCTL_set_acpi_reg is sufficient for both GPE and CPU map (or any 
> ACPI register should the need arise)

Well, my point is that as long as we continue to need
set_avail_vcpus (which I hear you say we do need), I'm not
sure the splitting would be helpful (minus the "albeit" part
above).

Jan


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