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Date:   Tue, 12 Jan 2021 01:09:23 +0100
From:   Borislav Petkov <>
To:     Krzysztof Mazur <>
Cc:     Thomas Gleixner <>,
        Ingo Molnar <>,,,
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

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



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