> -----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? Paul > Igor
