linux-kernel - Re: [PATCH v2 2/6] arm64: Move kill_cpu

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Date:	Tue, 1 Dec 2015 18:50:29 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
	linux-kernel@...r.kernel.org, will.deacon@....com,
	catalin.marinas@....com
Subject: Re: [PATCH v2 2/6] arm64: Move kill_cpu_early to smp.c

On Tue, Dec 01, 2015 at 06:10:17PM +0000, Suzuki K. Poulose wrote:
> On 01/12/15 17:52, Mark Rutland wrote:
> >On Tue, Dec 01, 2015 at 05:38:54PM +0000, Suzuki K. Poulose wrote:
> >>On 01/12/15 16:31, Mark Rutland wrote:
> >
> >[...]
> >
> >>>We need stuck-in-the-kernel flag to account for CPUs which didn't manage
> >>>to turn the MMU on (which are either in the spin-table, or failed when
> >>>they were individually onlined).
> >>
> >>Did you mean to say "turn the MMU off" ?
> >
> >No, I mean CPUs which were unable to turn the MMU on in the first place.
> >Perhaps they entered the spin-table but were never individually onlined,
> >perhaps they didn't support the kernel page size, etc.
> >
> >When CPUs exit the kernel via PSCI they never switch the MMU off within
> >the kernel.
> 
> OK. So the flag will also be used for CPUs which are stuck-in-the-kernel
> with MMU turned on. e.g, a CPU (using spin-table) we try to bring down
> in kill_cpu_early(). Correct ?

Yes.

We'd also pad it such that nothing else shares the same writeback
granule, and when writing to it with the MMU off we can invalidate the
stale cached copy.

Thanks,
Mark.
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