linux-kernel - Re: arm: v4.18-rc5 with cpuidle on TC2 (A7 boot) spectre v2 issue

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Message-ID: <20180719103919.GB19287@e105550-lin.cambridge.arm.com>
Date:   Thu, 19 Jul 2018 11:39:19 +0100
From:   Morten Rasmussen <morten.rasmussen@....com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Qais Yousef <Qais.Yousef@....com>
Subject: Re: arm: v4.18-rc5 with cpuidle on TC2 (A7 boot) spectre v2 issue

On Thu, Jul 19, 2018 at 11:01:10AM +0100, Russell King - ARM Linux wrote:
> On Thu, Jul 19, 2018 at 11:42:50AM +0200, Dietmar Eggemann wrote:
> > Hi,
> > 
> > running v4.18-rc5 (plus still missing "power: vexpress: fix corruption in
> > notifier registration", otherwise I get this rcu_sched stall issue) on TC2
> > (A7 boot) with vanilla multi_v7_defconfig plus
> > CONFIG_ARM_BIG_LITTLE_CPUIDLE=y gives me continuous:
> > 
> > ...
> >  CPUX: Spectre v2: incorrect context switching function, system vulnerable
> > ...
> > 
> > messages.
> > 
> > Work around is to disable CONFIG_HARDEN_BRANCH_PREDICTOR.
> 
> or disable big.Little if you want the hardening.
> 
> The choices are currently either protection against Spectre or big.Little
> support since the two are mutually exclusive at the moment.

Would it be possible to make those message only appear once like they do
when booting on A15?

As it is we have to change the default setting of this new option to
make the platform useable as those messages are flooding the console. I
see >40 messages per second.

Morten