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

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Message-ID: <433cec57-57a9-afff-22f3-68308eda682b@intel.com>
Date:   Mon, 12 Nov 2018 09:48:08 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org
Cc:     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 11/12/18 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.