linux-kernel - Re: [PATCH v3 2/4] x86/mmx: Use KFPU

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Date:   Thu, 21 Jan 2021 12:29:57 +0100
From:   Krzysztof Mazur <krzysiek@...lesie.net>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Krzysztof Olędzki <ole@....pl>,
        Arnd Bergmann <arnd@...db.de>, stable@...r.kernel.org
Subject: Re: [PATCH v3 2/4] x86/mmx: Use KFPU_387 for MMX string operations

On Wed, Jan 20, 2021 at 09:09:49PM -0800, Andy Lutomirski wrote:
> The default kernel_fpu_begin() doesn't work on systems that support XMM but
> haven't yet enabled CR4.OSFXSR.  This causes crashes when _mmx_memcpy() is
> called too early because LDMXCSR generates #UD when the aforementioned bit
> is clear.
> 
> Fix it by using kernel_fpu_begin_mask(KFPU_387) explicitly.
> 
> Fixes: 7ad816762f9b ("x86/fpu: Reset MXCSR to default in kernel_fpu_begin()")
> Cc: <stable@...r.kernel.org>
> Reported-by: Krzysztof Mazur <krzysiek@...lesie.net>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/lib/mmx_32.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)

Thanks, 5.10 + this patch series boots on K7 with SSE.

Tested-by: Krzysztof Mazur <krzysiek@...lesie.net>

Regards,
Krzysiek