Re: Help with Understanding vcpu xstate restore error during vm migration

[Fonyuy-Asheri Caleb <fonyuy-asheri.caleb@xxxxxxxx>]

> On 06.08.2024 09:34, Fonyuy-Asheri Caleb wrote:
>>> If what you say in the earlier paragraph was the case with upstream Xen and
>>> without you restricting what the guest being migrated was able to see on the
>>> source host, then I think that would indicate a bug somewhere. Yet you don't
>>> provide enough details to be certain.
>> 
>> Sorry for not specifying. I am still in the same context as stated 
>> previously.
>> I haven't made any modifications to xen and no restrictions on what the guest
>> can see.
> 
> Wasn't it the case that previously you observed AVX disabled, because of
> GDS? With AVX disabled, AVX512 would be implicitly disabled, too. Then

In my previous setup I wasn't able to confirm the GDS status because at the time
we mentioned it in discussions I no longer had access to the experiment 
environment. 

> migrating from an AVX512-capable host to an AVX512-incapable one would
> of course work. Yet of course this is only an example, because I don't
> know whether AVX512 is what your new inquiry would have been about. As
> indicated - please provide sufficient detail so we actually know what
> you're doing and what you observe.
> 
> Jan

Seems there's more to this than I think. Here's the entire information about my 
setup. 

Source Server: 
   Processor: Intel(R) Xeon(R) Platinum 8358 CPU @ 2.60GHz
   Xsave dependences(based on xen gen-cpuid.py): 
                     'fma', 'avx', 'f16c', 'avx2', 'avx512f', 'avx512dq', 
'avx512cd', 
                      'avx512bw', 'avx512vl', 'xsaveopt', 'xsavec', 'xgetbv1', 
'xsaves', 
                      'pku', 'avx512_vbmi2', 'vaes', 'vpclmulqdq', 
'avx512_vnni', 'avx512_bitalg', 
                      'avx512_vpopcntdq'


Target Server:
   Processor: Intel(R) Xeon(R) Gold 6130 CPU @ 2.10GHz
   Xsave dependencies: 
             'fma', 'avx', 'f16c', 'avx2', 'mpx', 'avx512f', 'avx512dq', 
             'avx512cd', 'avx512bw', 'avx512vl', 'xsaveopt', 'xsavec', 
'xgetbv1', 'xsaves', 'pku'

Operating System: Debian12 (on both source and target servers)
Guest OS: Ubuntu 18.04 (PV)

Xen version: 4.18.3-pre (commit 01f7a3c792241d348a4e454a30afdf6c0d6cd71c)


So I have the following which are available on my source server but not on the 
target server: 
'avx512_vbmi2', 'vaes', 'vpclmulqdq', 'avx512_vnni', 'avx512_bitalg', 
'avx512_vpopcntdq'

Per my current understanding, I would expect more xstates on the VM than 
supported on the target
server and hence a failure with xstate verification when restoring CPU state. 

However migrating a guest from Source to target works. 

Note that these extra avx512 features are all visible to the guest I migrate.

Caleb