On 9/23/20 9:50 AM, Jiri Denemark wrote: > Collin, I apologize for not getting to you earlier. > > On Wed, Sep 16, 2020 at 12:11:08 -0400, Collin Walling wrote: >> On 9/16/20 3:03 AM, Michal Privoznik wrote: >>> On 9/15/20 10:25 PM, Collin Walling wrote: >>>> One more ping in attempt to get this in the right direction. Otherwise >>>> I'll post my next idea and we can go from there :) >>> >>> I agree with Peter that while the idea might look correct it's too deep. >>> >>>> >>>> Thinking about this issue, should a host-passthough CPU definition be >>>> permitted for the baseline & comparison commands? The model represented >>>> under this mode is not considered migration safe and it may make sense >>>> to simply fail early since these commands aim to construct/determine a >>>> migratable CPU model, respectively. >>> >>> Honestly, I don't know much about this CPU models area, but is that true >>> even for two identical hosts? Say I have two desktops next to each >>> other, with the same CPU and I want to migrate. I could use host model, >>> couldn't I? >>> >> >> "Host-model" is an alias for a CPU model that closely represents the >> capabilities of the host machine (on s390, because this model is defined >> by the hypervisor, it can also be called the "hypervisor CPU model" -- >> not an important detail). >> >> However, a guest running with the host-passthrough mode is not >> considered migration safe as that guest may covertly run with >> features/capabilities that are not directly exposed to the hypervisor. > > Right, but migration may still be possible and working fine if both host > are identical. > >> From what I understand regarding the hypervisor-cpu-compare and >> hypervisor-cpu-baseline commands is that they aim to assist with >> determining the migratability of guests based on their CPU model and >> feature set (usually along with a host CPU in the equation as well). > > Baseline with a host-passthrough CPU is not indeed very useful, but Agreed, but I think baseline would still benefit from the error catching that is proposed in the CPU comparison patch (I continue the conversation over on that thread). > compare could still be used and its usage is not limited to migration. > For example, you can use it to check whether a domain with a guest CPU > configuration can be started on a specific host before you actually try > to start it. And reporting host-passthrough as incompatible would be > wrong. > > Anyway, thanks for your patch, it was mostly correct, it just needed to > be done a bit higher in the call graph. Incidentally, Tim Wiederhake [1] > took this original patch and moved the change to the right place. The > authorship is still yours, so if you want to append you signed-off-by > tag there, I'll wait a bit before pushing Tim's patch. Thanks. Gave my sign-off. > > Jirka > > [1] https://www.redhat.com/archives/libvir-list/2020-September/msg01177.html > -- Regards, Collin Stay safe and stay healthy
