linux-kernel - Re: [PATCH 07/11] x86/pkeys: Drop the preempt-disable section

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Date:   Fri, 12 Oct 2018 11:07:28 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 07/11] x86/pkeys: Drop the preempt-disable section

On Fri, Oct 12, 2018 at 10:58 AM Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> On 10/04/2018 07:05 AM, Sebastian Andrzej Siewior wrote:
> > The fpu->initialized flag should not be changed underneath us. This might be a
> > fallout during the removal of the LazyFPU support. The FPU is marked
> > initialized as soon as the state has been set to an initial value. It does not
> > signal if the CPU's FPU registers are loaded.
>
> If this is true, then the check for fpu->initialized should also go away.
>

All these "if" statements in the FPU code are messy and make
understanding and reviewing this code hard.

Can you prepare a patch for the beginning of your series that removes
fpu->initialized and just ensures that the fpu is always initialized?
This will regress performance, but you should get all that performance
back with TIF_LOAD_FPU.