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Re: [Xen-devel] PVH VCPU hotplug support v7?

On 07/31/2017 11:36 AM, Ross Lagerwall wrote:
> On 07/31/2017 03:29 PM, Boris Ostrovsky wrote:
>> On 07/31/2017 10:12 AM, Andrew Cooper wrote:
>>> On 31/07/17 14:55, Boris Ostrovsky wrote:
>>>> On 07/31/2017 09:20 AM, Ross Lagerwall wrote:
>>>>> Hi Boris,
>>>>> I've modified your PVH VCPU hotplug support v6 patch series [1] to
>>>>> support HVM guests running _with_ a device model for XenServer's
>>>>> purposes. This is useful because it moves the vCPU hotplug handling
>>>>> out of QEMU and allows it to mostly be shared with PVH. It will also
>>>>> allow unplugging vCPUs (libxl currently only does cpu-add for
>>>>> upstream
>>>>> qemu).
>>>>> Are you still planning on continuing with that patch series since
>>>>> your
>>>>> commit to Linux [2]?
>>>> This series has been put on hold until we figure out what to do with
>>>> hotplug for PVH dom0. (The problem was the "dual" view by dom0 of APCI
>>>> CPU namespace --- on hotplug event dom0 has to somehow figure out
>>>> whether the event was due to (dis)appearance of a physical or
>>>> virtual CPU).
>>>> I don't think this has been dealt with yet (copying Roger).
>>>  From the point of view of unblocking several pieces of work, it
>>> would be
>>> fine for this logic to be behind an emulation flag, just like
>>> LAPIC/etc.
>> The (I think) last message discussing this series was
>> https://lists.xenproject.org/archives/html/xen-devel/2017-01/msg00143.html
>> Are you suggesting extracting pieces that would move hotplug support for
>> HVM guests from qemu to hypervisor/toolstack but leave all PVH-specific
>> code out? (The feature flag is part of this series ---
>> https://lists.xenproject.org/archives/html/xen-devel/2017-01/msg00059.html)
> I think(?) Andrew was suggesting to have an emulation flag such that
> hotplug support is moved into the hypervisor for HVM guests _and_ PVH
> guests except for PVH dom0.

That (different handling for PVH dom0 vs. domU) was exactly what Jan was
objecting to. (I'll add him too).


> I don't know what work this unblocks that he was referring to.

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