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Date:   Mon, 19 Nov 2018 16:19:48 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Borislav Petkov <bp@alien8.de>, x86@kernel.org,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Rik van Riel <riel@surriel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH] x86/fpu: Disable BH while while loading FPU registers in
 __fpu__restore_sig()
Message-ID: <20181119151948.g27vuuavpgmyqynn@linutronix.de>
References: <20181108145721.GC7543@zn.tnic>
 <20181109173521.2m6iijp5wkncgi77@linutronix.de>
 <20181109185202.GF21243@zn.tnic>
 <20181109232521.l2ll2n3coxygkxv4@linutronix.de>
 <20181112155643.vclej44qzg3pmbow@linutronix.de>
 <433cec57-57a9-afff-22f3-68308eda682b@intel.com>
 <20181119114151.e4mbs7ktfjojl3uf@linutronix.de>
 <982af52b-4e39-2b26-a184-2fe13f3d9f61@intel.com>
 <20181119150656.ylbrsvchdyavms4w@linutronix.de>
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On 2018-11-19 07:08:44 [-0800], Dave Hansen wrote:
> On 11/19/18 7:06 AM, Sebastian Andrzej Siewior wrote:
> > On 2018-11-19 07:04:35 [-0800], Dave Hansen wrote:
> >> Does the local_bh_disable() itself survive?
> > Not in __fpu__restore_sig(). I do have:
> > | static inline void __fpregs_changes_begin(void)
> > | {
> > |        preempt_disable();
> > |        local_bh_disable();
> > | }
> > 
> > and __fpregs_changes_begin() is introduced as part of the series.
> 
> OK, so can we just comment *that*, please?  Basically, why do we need botj?

let me do this then.
local_bh_disable() should be enough. However I had a discussion with
PeterZ that this (local_bh_disable()) also acting as preempt_disable())
is an implementation detail and should be avoided. It is not true
Preempt-RT for instance.

Sebastian