Re: [Xen-devel] Debugging Windows HVM crashes on Ryzen 3xxx series CPUs.

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.10.2019 07:22, Jürgen Groß wrote:
> On 25.10.19 19:01, Andrew Cooper wrote:
>> On 24/10/2019 12:57, Steven Haigh wrote:
>>> Hi all,
>>>
>>> I've managed to get the git master version of Xen on this affected
>>> system and tries to boot a Windows Server 2016 system. It crashes as
>>> per normal.
>>>
>>> I managed to get these logs, but I'm not quite sure what else to do to
>>> debug this issue further.
>>
>> After a collaborative debugging session on IRC, we've identified the
>> problem.  Here is a summary.
>>
>> https://www.reddit.com/r/Amd/comments/ckr5f4/amd_ryzen_3000_series_linux_support_and/
>> is concerning KVM, but it identified that the TOPOEXT feature was
>> important to getting windows to boot.
>>
>> Xen doesn't currently offer TOPOEXT to guests at all.  Fixing this is on
>> the TODO list along with the rest of the topology representation swamp.
>>
>> On a hunch, I offered up a XenServer patch which we are still using, in
>> lieu of fixing topology properly.  It is logically a revert of
>> ca2eee92df44 as that change wasn't migration safe.
>>
>> With this patch in place, windows works fine.  However, I don't think
>> the patch is appropriate to take into 4.13.
>>
>> Furthermore, there is no chance of getting the topology work sorted in
>> the remaining 4.13 timeframe.
>>
>> I'm at a loss for ideas, other than release note it as broken and make
>> fixing it a blocker for 4.14.
>>
>> Thoughts?
> 
> What about a domain config entry defaulting to "off" selecting the
> topology modification in libxc you provided for the test? That would
> just require to add a bool parameter to xc_cpuid_apply_policy(). It
> might even be possible to select the setting on the affected hardware
> automatically.

Except that to alter behavior as little as possible, we'd perhaps
better restrict this to affected Windows versions, or at most to
Windows in general. Linux after all looks to be sufficiently fine
with the hacked up CPUID data we provide.

Jan

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