linux-kernel - Re: [PATCH] x86/fpu: Reset MXCSR to default in kernel_fpu

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Message-ID: <20200616180123.GL13515@zn.tnic>
Date:   Tue, 16 Jun 2020 20:01:23 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     x86-ml <x86@...nel.org>, jpa@...nelbug.mail.kapsi.fi,
        Dave Hansen <dave.hansen@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/fpu: Reset MXCSR to default in kernel_fpu_begin()

On Tue, Jun 16, 2020 at 09:53:39AM -0700, Andy Lutomirski wrote:
> On Tue, Jun 16, 2020 at 2:53 AM Borislav Petkov <bp@...en8.de> wrote:
> >
> > Ok,
> >
> > here's the fix first so that it goes in. I'll hammer on the test case later.
> 
> Does the 32-bit case need FNINIT?

Pasting from IRC:

I'm thinking if you'd need to reinit the FPU, then you need to do it for
both, not only 32-bit or do you mean something else? Also, if you end up
doing FNSAVE (old CPU) that one reinits state.

Whatever we decide doing, this should be a separate patch anyway.

Thx.

-- 
Regards/Gruss,
    Boris.

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