linux-kernel - Re: [PATCH 10/11] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD

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Message-ID: <20181015152431.GD11434@zn.tnic>
Date:   Mon, 15 Oct 2018 17:24:31 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Rik van Riel <riel@...riel.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH 10/11] x86/fpu: prepare copy_fpstate_to_sigframe for
 TIF_LOAD_FPU

On Fri, Oct 12, 2018 at 12:40:19PM -0700, Dave Hansen wrote:
> > +	__fpregs_changes_end();
> 
> Do we really need the __fpregs_changes_*() abstraction for this single
> call site?

Yap, I'm staring at those in patch 2, there's no documentation there what
they're supposed to do, only the commit message of patch 11 says:

"The __fpregs_changes_{begin|end}() section ensures that the register
remain unchanged. Otherwise a context switch or a BH could save the
registers to its FPU context and processor's FPU register would remain
random."

So I'd say we should drop that abstraction, use preempt_* and put that
text above the single usage site.

Thx.

-- 
Regards/Gruss,
    Boris.

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