On 08/01/2021 11:40, Paul Durrant wrote: >> -----Original Message----- >> From: Igor Druzhinin <igor.druzhi...@citrix.com> >> Sent: 08 January 2021 11:36 >> To: p...@xen.org; xen-devel@lists.xenproject.org >> Cc: w...@xen.org; i...@xenproject.org; anthony.per...@citrix.com; >> andrew.coop...@citrix.com; >> george.dun...@citrix.com; jbeul...@suse.com; jul...@xen.org; >> sstabell...@kernel.org; >> roger....@citrix.com >> Subject: Re: [PATCH 2/2] viridian: allow vCPU hotplug for Windows VMs >> >> On 08/01/2021 11:33, Paul Durrant wrote: >>>> -----Original Message----- >>>> From: Igor Druzhinin <igor.druzhi...@citrix.com> >>>> Sent: 08 January 2021 11:30 >>>> To: p...@xen.org; xen-devel@lists.xenproject.org >>>> Cc: w...@xen.org; i...@xenproject.org; anthony.per...@citrix.com; >>>> andrew.coop...@citrix.com; >>>> george.dun...@citrix.com; jbeul...@suse.com; jul...@xen.org; >>>> sstabell...@kernel.org; >>>> roger....@citrix.com >>>> Subject: Re: [PATCH 2/2] viridian: allow vCPU hotplug for Windows VMs >>>> >>>> On 08/01/2021 08:38, Paul Durrant wrote: >>>>>> -----Original Message----- >>>>>> From: Igor Druzhinin <igor.druzhi...@citrix.com> >>>>>> Sent: 08 January 2021 00:47 >>>>>> To: xen-devel@lists.xenproject.org >>>>>> Cc: p...@xen.org; w...@xen.org; i...@xenproject.org; >>>>>> anthony.per...@citrix.com; >>>>>> andrew.coop...@citrix.com; george.dun...@citrix.com; jbeul...@suse.com; >>>>>> jul...@xen.org; >>>>>> sstabell...@kernel.org; roger....@citrix.com; Igor Druzhinin >>>>>> <igor.druzhi...@citrix.com> >>>>>> Subject: [PATCH 2/2] viridian: allow vCPU hotplug for Windows VMs >>>>>> >>>>>> If Viridian extensions are enabled, Windows wouldn't currently allow >>>>>> a hotplugged vCPU to be brought up dynamically. We need to expose a >>>>>> special >>>>>> bit to let the guest know we allow it. It appears we can just start >>>>>> exposing >>>>>> it without worrying too much about compatibility - see relevant QEMU >>>>>> discussion here: >>>>>> >>>>>> https://patchwork.kernel.org/project/qemu-devel/patch/1455364815-19586-1-git-send-email- >>>>>> d...@openvz.org/ >>>>> >>>>> I don't think that discussion really confirmed it was safe... just that >>>>> empirically it appeared to >>>> be so. I think we should err on >>>>> the side of caution and have this behind a feature flag (but I'm happy >>>>> for it to default to on). >>>> >>>> QEMU was having this code since 2016 and nobody complained is good >>>> enough for me - but if you insist we need an option - ok, I will add one. >>>> >>> >>> Given that it has not yet been in a release, perhaps you could just guard >>> this and the >> implementation of leaf 0x40000005 using HVMPV_ex_processor_masks? >> >> That looks sloppy and confusing to me - let's have a separate option instead. >> > > Yes, for this I guess it is really a separate thing. Using > HVMPV_ex_processor_masks to control the presence of leaf 0x40000005 seems > reasonable (since it's all about being able to use >64 vcpus). Perhaps a new > HVMPV_cpu_hotplug for this one?
Agree. Igor
