linux-kernel - Re: [RFC PATCH] x86/delay: Do not use cpu_tss in preemptible ctxt in delay

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Message-ID: <CALCETrVGaPASf=r7Z3aSQ1aM7EmHfT1y5QBK6Gss-M=++D+wUw@mail.gmail.com>
Date:	Wed, 9 Mar 2016 09:56:39 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Huang Rui <ray.huang@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	spg_linux_kernel@....com, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86/delay: Do not use cpu_tss in preemptible ctxt in delay_mwaitx()

On Mar 9, 2016 3:38 AM, "Borislav Petkov" <bp@...en8.de> wrote:
>
> From: Borislav Petkov <bp@...e.de>
>
> So Andy had a good idea about using a cacheline-aligned, seldomly used
> per-cpu var as the MONITORX target but we can't use it in preemptible
> context. The first simple idea I have is to disable preemption around us
> dereffing it.

What's the actual problem?  Is it the preempt warnings and, if so,
would raw_cpu_ptr fix it?

It may pay to move it into the loop, though.

--Andy