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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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 whether to split the other two, or simply send SCI whenever
> GPE bits have been modified depends on the specific requirements
> the ACPI spec puts on us. Or maybe it could always be folded,
> with (if necessary) SCI sending being controlled by a flag.
True. The spec says that all ACPI events generate an SCI.

-boris

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