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Date: Thu, 6 Dec 2018 12:39:56 +0000
From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Krzysztof Kozlowski <krzk@kernel.org>
Subject: Re: [PATCH v2 5/5] ARM: spectre-v2: per-CPU vtables to work around
 big.Little systems
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On Thu, Dec 06, 2018 at 11:24:27AM +0100, Krzysztof Kozlowski wrote:
> On Thu, 6 Dec 2018 at 11:01, Russell King - ARM Linux
> <linux@armlinux.org.uk> wrote:
> > I've no idea based on what you've supplied given that the SoC
> > maintainers are responsible for writing the code to deal with hotplug
> > etc, and Exynos's code there is something of a maze.  It's not clear
> > which bits are being used.  I think you at the very least need to debug
> > to find out whether the problem is at CPU down or CPU up.
> >
> > From the ARM architecture point of view, for Cortex A9, all the
> > processor function instances should be identical.  The only difference
> > as a result of the patch is that we'll be calling smp_processor_id()
> > early (which should be fine), and indirecting through the cpu_vtable[]
> > array rather than merely dereferencing the processor struct.
> >
> > What about checking dmesg - messages from offline CPUs do not appear
> > on the console(s) but are still logged in the kernel log.
> >
> > You could try making PROC_VTABLE() the same as PROC_TABLE() (iow,
> > always access cpu_vtable[0]) to see whether it's the smp_processor_id()
> > that's causing your problem or not.  If it is, then try and work out
> > which of the processor functions is causing it by restoring
> > PROC_VTABLE() and then switching each from PROC_VTABLE() to
> > PROC_TABLE() until it does work.
> 
> Thanks for hints!

So I can plan, how long do you think it will take to get some results
from my suggestions above?

-- 
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