linux-kernel - Re: [PATCH] x86/lib: don't use MMX before FPU initialization

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Message-ID: <20210112000923.GK25645@zn.tnic>
Date:   Tue, 12 Jan 2021 01:09:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Krzysztof Mazur <krzysiek@...lesie.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/lib: don't use MMX before FPU initialization

On Mon, Dec 28, 2020 at 05:06:31PM +0100, Krzysztof Mazur wrote:
> When enabled, the MMX 3DNow! optimized memcpy() is used very early,
> even before FPU is initialized. It worked fine, but commit
> 7ad816762f9bf89e940e618ea40c43138b479e10 ("x86/fpu: Reset MXCSR
> to default in kernel_fpu_begin()") broke that. After that commit
> the kernel crashes just after "Booting the kernel." message.

Have you figured out in the meantime what exactly is causing the
breakage?

Does it boot if you comment out

+       if (boot_cpu_has(X86_FEATURE_FPU))
+               asm volatile ("fninit");

in kernel_fpu_begin()?

I'm guessing K7 doesn't have X86_FEATURE_XMM so the LDMXCSR won't
matter...

Thx.

-- 
Regards/Gruss,
    Boris.

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