linux-kernel - Re: [PATCH 09/11] x86: rework CONFIG_GENERIC

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Message-Id: <6465b995-a1d2-422b-b1f2-5e1a0b3163bb@app.fastmail.com>
Date: Thu, 05 Dec 2024 11:47:24 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Andy Shevchenko" <andy@...nel.org>
Cc: "Linus Torvalds" <torvalds@...ux-foundation.org>,
 "Arnd Bergmann" <arnd@...nel.org>, linux-kernel@...r.kernel.org,
 x86@...nel.org, "Thomas Gleixner" <tglx@...utronix.de>,
 "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, "Matthew Wilcox" <willy@...radead.org>,
 "Sean Christopherson" <seanjc@...gle.com>,
 "Davide Ciminaghi" <ciminaghi@...dd.com>,
 "Paolo Bonzini" <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 09/11] x86: rework CONFIG_GENERIC_CPU compiler flags

On Thu, Dec 5, 2024, at 11:01, Andy Shevchenko wrote:
> On Thu, Dec 05, 2024 at 10:46:25AM +0100, Arnd Bergmann wrote:
>> On Thu, Dec 5, 2024, at 00:33, Linus Torvalds wrote:
>> > On Wed, 4 Dec 2024 at 11:44, Arnd Bergmann <arnd@...db.de> wrote:
>
> ...
>
>> I did come across a remaining odd problem with this, as Crusoe and
>> GeodeLX both identify as Family 5 but have CMOV.  Trying to use
>> a CONFIG_M686+CONFIG_X86_GENERIC on these runs fails with a boot
>> error "This kernel requires a 686 CPU but only detected a 586 CPU".
>
> It might be also that Intel Quark is affected same way.

No, as far as I can tell, Quark correctly identifies as Family 5
and is lacking CMOV. It does seem though that it's currently
impossible to configure a kernel for Quark that uses PAE/NX,
because there is no CONFIG_MQUARK and it relies on building
with CONFIG_M586TSC. If anyone still cared enough about it,
they could probably add an MQUARK option that has lets
you build the kernel with -march=i586 -mtune=i486 and
optional PAE.

The only other one that perhaps gets misidentified is the IDT
Winchip that is claimed to support cmpxchg64b but only
identifies as Family 4. It's even less likely that anyone
cares about this one than the Quark.

     Arnd