> -----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? Paul > Igor
