Re: [Xen-devel] [PATCH 00/10] PVH VCPU hotplug support

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/11/16 21:42, Boris Ostrovsky wrote:
> This series adds support for ACPI-based VCPU hotplug for unprivileged
> PVH guests.
>
> New XEN_DOMCTL_set_avail_vcpus is introduced and is called during
> guest creation and in response to 'xl vcpu-set' command. This domctl
> updates GPE0's status and enable registers and sends an SCI to the
> guest using (newly added) VIRQ_SCI.

Thankyou for doing this.  Getting APCI hotplug working has been a low
item on my TODO list for while now.

Some queries and comments however.

This series is currently very PVH centric, to the point of making it
unusable for plain HVM guests.  While I won't insist on you implementing
this for HVM (there are some particularly awkward migration problems to
be considered), I do insist that its implementation isn't tied
implicitly to being PVH.

The first part of this will be controlling the hypervisor emulation of
the PM1* blocks with an XEN_X86_EMU_* flag just like all other emulation.

>
>
> Boris Ostrovsky (10):
>   x86/domctl: Add XEN_DOMCTL_set_avail_vcpus

Why is this necessary?  Given that a paravirtual hotplug mechanism
already exists, why isn't its equivalent mechanism suitable?

>   acpi: Define ACPI IO registers for PVH guests

Can Xen use pm1b, or does there have to be a pm1a available to the guest?

>   pvh: Set online VCPU map to avail_vcpus
>   acpi: Power and Sleep ACPI buttons are not emulated

PVH might not want power/sleep, but you cannot assume that HVM guests
have a paravirtual mechnism of shutting down.

>   acpi: Make pmtimer optional in FADT
>   acpi: PVH guests need _E02 method

Patch 6 Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

>   pvh/ioreq: Install handlers for ACPI-related PVH IO accesses

Do not make any assumptions about PVHness based on IOREQ servers.  It
will not be true for usecases such as vGPU.

~Andrew

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