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

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Message-ID: <Y7YDz/8lsVigmeXF@zn.tnic>
Date:   Wed, 4 Jan 2023 23:55:11 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 1/3] x86/cpu: Process all CPUID dependencies after
 identifying CPU info

On Wed, Jan 04, 2023 at 09:02:04PM +0000, Sean Christopherson wrote:
> And there's a non-zero chance we'd end up with a kernel param to allow booting
> unknown CPUs, e.g. for people doing weird things with VMs or running old, esoteric
> hardware.  At that point we'd end up with a more complex implementation than
> processing dependencies on synthetic flags, especially if there's ever a more
> legitimate need to process such dependencies.

I'm sorry but I'm still unclear on what actual use care are we even fixing here?

If it is about people who'd like to tinker with old hw or doing weird VM things,
they can just as well adjust their kernel .configs and rebuild.

Peeking around your patchset, if all this is about dropping the
X86_FEATURE_MSR_IA32_FEAT_CTL check and checking only X86_FEATURE_VMX and in
order to do that, you want to cover those obscure cases where
init_ia32_feat_ctl() won't get run, then sure, I guess - changes look simple
enough. :)

-- 
Regards/Gruss,
    Boris.

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