Re: [PATCH] x86/cpu/centaur: Disable X86_FEATURE_FSGSBASE on Zhaoxin C4600

[Yao Zi <me@ziyao.cc>]

On Sat, Feb 28, 2026 at 04:33:18PM -0800, Dave Hansen wrote:
> On 2/28/26 09:37, Yao Zi wrote:
> > Let's disable the feature on this problematic CPU and warn the user
> > about the quirk. x86_model_id is used to match the platform to avoid
> > unexpectedly breaking other CentaurHauls cores with conflicting
> > family/model ID.
> 
> Wait a sec. There are lots of different microarchitectures with the same
> family/model and no other way to identify them but the model id string?
> 
> We've used string in a handful of places, but it's an absolute last
> resort. Are you *sure* there's no stepping or anything?

No. The commit message should be more clear, I have no clue that there
are other designs with the same family/model/stepping combination.
However, C4600 is a design from Zhaoxin instead of VIA but using
CentaurHauls as vendor ID, thus conflicts may happen since they're
different entities. So I take the safest way.

> I kinda think we should keep this like all the other vendors and keep it
> to model/family/stepping. If the vendor has grouped too many
> non-vulnerable CPUs under that, then ... this is going to be a good
> learning to bring back to the CPU design team.
> 
> If you're changing the CPU in a way that it's possible to regress
> things, you *need* to bump the model or stepping. Period. If you don't,
> the baby might get thrown out with the bathwater.
> 
> Please resend this with a normal x86_match_cpu() and x86_cpu_id[] array.

The concerns may be too farsight as there's no clue indicating conflicts
actually happened. I'll take the change in v2 if you still think it's
appropriate.

Regards,
Yao Zi