linux-kernel - Re: [PATCH] x86/fpu: Disable BH while while loading FPU registers in __fpu__restore

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Message-ID: <982af52b-4e39-2b26-a184-2fe13f3d9f61@intel.com>
Date:   Mon, 19 Nov 2018 07:04:35 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.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>,
        Rik van Riel <riel@...riel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH] x86/fpu: Disable BH while while loading FPU registers in
 __fpu__restore_sig()

On 11/19/18 3:41 AM, Sebastian Andrzej Siewior wrote:
> On 2018-11-12 09:48:08 [-0800], Dave Hansen wrote:
>> On 11/12/18 7:56 AM, Sebastian Andrzej Siewior wrote:
>>> Use local_bh_disable() around the restore sequence to avoid the race. BH
>>> needs to be disabled because BH is allowed to run (even with preemption
>>> disabled) and might invoke kernel_fpu_begin().
>> FWIW, that would make nice comment fodder for the local_bh_disable().
>> I'd much rather run into it there than in a changelog.
> Hmm. Should I really resent a v2 of this with the additional comment?
> This patch should go stable to the fix the bug and at the end of this
> series I remove/replace this hunk anyway.
> I can do either way, just wanted to check first.

Does the local_bh_disable() itself survive?