linux-kernel - Re: [PATCH] x86/microcode: Fix crashes on early 486 CPUs due to usage of 'cpuid'.

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Message-Id: <20250406174633.2c581923c145687476191753@ombertech.com>
Date: Sun, 6 Apr 2025 17:46:33 +1000
From: Kevin Koster <lkml@...ertech.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Oerg866 <oerg866@...glemail.com>, linux-kernel@...r.kernel.org, Thomas
 Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Dave Hansen
 <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin"
 <hpa@...or.com>
Subject: Re: [PATCH] x86/microcode: Fix crashes on early 486 CPUs due to
 usage of 'cpuid'.

On Sun, 6 Apr 2025 16:40:49 +1000
Kevin Koster <lkml@...ertech.com> wrote:
> On Sat, 5 Apr 2025 11:32:26 +0200
> Borislav Petkov <bp@...en8.de> wrote:
> > On Sat, Apr 05, 2025 at 01:03:06PM +1100, Kevin Koster wrote:
> > > On Sat, 19 Oct 2024 08:29:04 +0200
> > > Oerg866 <oerg866@...glemail.com> wrote:
> > > > Starting with v6.7-rc1, the kernel was no longer able to boot on
> > > > early i486-class CPUs.
> > > 
> > > Thanks for this patch! It solves my problem with kernel 6.12.11
> > > rebooting at start-up on 486 CPUs, which had me puzzled. (tested
> > > on AM486DX2-66 and CX486DX4-100)
> > > 
> > > Is there a reason why the patch wasn't accepted?
> > 
> > Yes, too many patches, too little time. :-(
> > 
> > Anyway, does the one below - only build-tested - work for both y'all
> > too?
> 
> On my AM486DX2-66 it gets past the immediate reboot problem but gets
> an Oops and kernel panic here:

But if I move "cpuid_1_eax = native_cpuid_eax(1);" to after the
microcode_loader_disabled() check in amd.c, like in the first patch, it
boots fine!