Re: Question about migrate the vm with host-passthrough cpu

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.

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