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

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Message-ID: <20250407135533.GDZ_PZVZ-2CKmhbt7d@fat_crate.local>
Date: Mon, 7 Apr 2025 15:55:33 +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 Tue, Apr 08, 2025 at 12:21:50AM +1000, Kevin Koster wrote:
> To rephrase: I like knowing that "CONFIG_M486=y" works, in the kernel
> configuration. If not, then I know to use other OSs if I want to boot a
> 486.

Lemme put it this way: off and on the topic about removing 32-bit support
altogether comes up but we never go through with it. One day we might though.

:-)

> For email/news every morning, then a (newer) laptop afterwards.

Oh boy.

> --- a/arch/x86/kernel/cpu/microcode/amd.c
> +++ b/arch/x86/kernel/cpu/microcode/amd.c
> @@ -1093,7 +1093,7 @@
>  
>  static int __init save_microcode_in_initrd(void)
>  {
> -	unsigned int cpuid_1_eax = native_cpuid_eax(1);
> +	unsigned int cpuid_1_eax;
> 	struct cpuinfo_x86 *c = &boot_cpu_data;
> 	struct cont_desc desc = { 0 };
> 	enum ucode_state ret;
> @@ -1102,6 +1102,8 @@
> 	if (microcode_loader_disabled() || c->x86_vendor != X86_VENDOR_AMD || c->x86 < 0x10)
> 		return 0;
>  
> +	cpuid_1_eax = native_cpuid_eax(1);
> +
> 	if (!find_blobs_in_containers(&cp))
> 		return -EINVAL;

Yah, thanks. I must be going blind. :-(

It is all clear now - I'll run the fix on my machines some more and then post
a proper patch.

Thx.

-- 
Regards/Gruss,
    Boris.

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