Re: [PATCH 1/3] x86/cpu: Process all CPUID dependencies after identifying CPU info

[Borislav Petkov]

On Thu, Dec 08, 2022 at 04:26:29PM +0000, Sean Christopherson wrote:
> But it's not really a hardware issue either.  More like an admin/user issue.
> 
> The problem is that if a kernel is built for subset of CPU types, e.g. just Intel
> or just Centaur, and then booted on an "unsupported" CPU type, init_ia32_feat_ctl()
> will never be invoked because ->c_init() will point a default_init(), and so the
> kernel never checks MSR_IA32_FEAT_CTL to see if VMX and/or SGX are fully enabled.

Yeah, you called it an "edge case". I'm wondering whether we should even
worry about that case...

I mean, the majority of Linuxes out there are allmodconfig-like kernels
and booting on unsupported CPU type doesn't happen.

Hell, I'd even say that if you attempt booting on unsupported CPU type,
we should simply fail that boot attempt.

I.e., what validate_cpu() does in some cases.

IOW, I don't mind what you're doing but I wonder whether we should even
go the trouble to do so or simply deny that by saying "Well, don't do
that then".

Hmmm.

-- 
Regards/Gruss,
    Boris.

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