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

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Message-ID: <20250407102927.GAZ_OpBw5hJ2QTFsKz@fat_crate.local>
Date: Mon, 7 Apr 2025 12:29:27 +0200
From: Borislav Petkov <bp@...en8.de>
To: Kevin Koster <lkml@...ertech.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Oerg866 <oerg866@...glemail.com>,
	linux-kernel@...r.kernel.org, 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 Mon, Apr 07, 2025 at 09:58:48AM +1000, Kevin Koster wrote:
> But I like to know Linux really works on the hardware it's built for,

I don't know what that means.

> and I'm not much better, writing this now on a Pentium 1.

Lemme guess: this is your main machine you use for daily work?

:-\

> > -	if (dis_ucode_ldr || c->x86_vendor != X86_VENDOR_AMD || c->x86 < 0x10)
> > +	if (microcode_loader_disabled() || c->x86_vendor != X86_VENDOR_AMD || c->x86 < 0x10)
> 		return 0;
> 
> Still fails unless the native_cpuid_eax(1) call is moved under here. After that
> change, it boots fine.

Please show me with a diff what you're doing because I don't know what you
mean.

I did this:

bool have_cpuid_p(void)
{
        return false;
}

in order to simulate no CPUID support but my 32-bit guest boots fine.

Also, send a full dmesg from that machine so that I can try to reproduce here.

Thx.

-- 
Regards/Gruss,
    Boris.

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