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

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Message-ID: <20250405205013.GCZ_GXhYBEsH73q1MC@fat_crate.local>
Date: Sat, 5 Apr 2025 22:50:13 +0200
From: Borislav Petkov <bp@...en8.de>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Kevin Koster <lkml@...ertech.com>, 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
Subject: Re: [PATCH] x86/microcode: Fix crashes on early 486 CPUs due to
 usage of 'cpuid'.

On Sat, Apr 05, 2025 at 01:33:46PM -0700, H. Peter Anvin wrote:
> How the Hades does c->x86 not get set to 4 (hence < 0x10) on this CPU?
> 
> That's the real bug imo...

Go to the first mail in the thread.

4c585af7180c ("x86/boot/32: Temporarily map initrd for microcode loading")

walks straight into  native_cpuid_ecx().

Which reminds me - I should remove that have_cpuid_p() in load_ucode_bsp() now
too and move the disabled check up.

-- 
Regards/Gruss,
    Boris.

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