linux-kernel - Re: [PATCH 2/4] Revert "x86/boot: Fail the boot if !M486 and CPUID is missing"

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Message-ID: <CALCETrWzCH7n7zqs278-mXiceP9jjt6T+ZkLhdqa05kGg7QHbQ@mail.gmail.com>
Date:   Thu, 1 Dec 2016 16:33:17 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Matthew Whitehead <tedheadster@...il.com>,
        Henrique de Moraes Holschuh <hmh@....eng.br>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/4] Revert "x86/boot: Fail the boot if !M486 and CPUID is missing"

On Thu, Dec 1, 2016 at 1:02 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Thu, Dec 01, 2016 at 06:53:50AM +0100, Peter Zijlstra wrote:
>> On Wed, Nov 30, 2016 at 12:34:53PM -0800, Andy Lutomirski wrote:
>> > This reverts commit ed68d7e9b9cfb64f3045ffbcb108df03c09a0f98.
>> >
>> > The patch wasn't quite correct -- there are non-Intel (and hence
>> > non-486) CPUs that we support that don't have CPUID.  Since we no
>> > longer require CPUID for sync_core(), just revert the patch.
>>
>> Might be useful to enumerate which special parts these are.
>
> Right, and since we test for CPUID support at early boot, I think we
> should use the X86_FEATURE_CPUID aspect from what I proposed earlier:
>
> https://lkml.kernel.org/r/20161120111917.pw3alolx4fksfwbv@pd.tnic

Maybe we should just make the kernel work fully without CPUID.  There
isn't much to do on top of your patch -- I think we mainly want to
make the cpuid driver refuse to load.

--Andy