Re: [PATCH v3] x86/cpufeatures: Make X86_FEATURE_SHSTK clearcpuid-able

[Borislav Petkov]

On Thu, May 14, 2026 at 06:23:29PM +0000, Edgecombe, Rick P wrote:
> I didn't mean to support disabling them all. I meant have a thing with the same
> format as clearcpuid, but only works for features we want to support. So maybe
> like disable=usershstk. And then have just less code to have to cover all the
> nofoo cases. It would only support limited bits that were intentionally added.
> 
> This is not a well thought out idea though.

I can see that...

If you want to disable things, then you need to disable them properly. Like
turn off CR4 bits in this case or disable dependent features in other cases.
Or whatever else is needed.

Whatever you do, it needs to have a use case and be properly done.

clearcpuid= is simply shooting down X86_FEATURE flags. Not really well thought
out but a wholesale quick'n'dirty method of toggling feature bits (yah,
there's the setcpuid= counterpart too). And that's why it should not really
exist but that ship has sailed...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette