[Catching up with libvirt-users list after a long while ... hence the delay in my response.] On Fri, Feb 26, 2021 at 03:58:21PM +0800, Guoyi Tu wrote: > Thanks for you reply. > > I checked the qemu code, the destination qemu instance actually exposed > the cpu feature of new host , and if execute the cpuid instruction in > Guest OS after migration the family/model/stepping is the same as new > host. Just to reinforce Daniel's point below: 'host-passthrough' and live migration is tricky ... so the safest suggestion is to go with identical physical CPUs on source and destination hosts, along with identical kernel, _and_ CPU microcode versions (see the performance counters point below; and also thanks to Meltdown/Spectre). Or else live migration is very much likely to fail. > On Thu, 2021-02-25 at 14:10 +0000, Daniel P. Berrangé wrote: > > On Wed, Feb 24, 2021 at 09:42:37PM +0800, Guoyi Tu wrote: [...] > > The CPUID features are the biggest compatibility issue that is likely > > to cause problems generally, but I believe there can be others. > > > > For example if performance counters are exposed to the guest, these > > are likely to vary between different CPU models. Even different BIOS > > settings can change performance counters exposed by a CPU (HT vs no- > > HT) > > > > There might also be problems with CPU TSC frequency differences > > between > > the hosts. > > > > > I've test the case in my environment, and the migration succeeds, > > > the cpu > > > family/model/stepping and features of lscpu in Guest OS is the > > > same. > > > > Right, the issue is that the migration appears to succeed from QEMU's > > POV, but the guest may none the less see incompatibilities which > > result in a crash or incorrect behaviour an arbitrary amount of time > > later. It is really hard to guarantee that behaviour is going to be > > correct in all scenarios. > > > > Personally I would consider the use of host-passthrough to be > > unsupportable > > in production environment, unless the CPUs are all homogeneous. > > > > Regards, > > Daniel > > -- /kashyap
