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.