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. Igor
