linux-kernel - Re: [RFC PATCH v3 4/8] arm64: Handle early CPU boot failures

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Message-ID: <20151216113617.GC6412@leverpostej>
Date:	Wed, 16 Dec 2015 11:36:17 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Will Deacon <will.deacon@....com>
Cc:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>,
	catalin.marinas@....com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com
Subject: Re: [RFC PATCH v3 4/8] arm64: Handle early CPU boot failures

On Wed, Dec 16, 2015 at 11:29:15AM +0000, Will Deacon wrote:
> On Wed, Dec 16, 2015 at 10:39:50AM +0000, Suzuki K. Poulose wrote:
> > On 15/12/15 11:55, Will Deacon wrote:
> > >On Wed, Dec 09, 2015 at 09:57:15AM +0000, Suzuki K. Poulose wrote:
> > 
> > >>  /*
> > >>   * Initial data for bringing up a secondary CPU.
> > >>+ * @stack  - sp for the secondary CPU
> > >>+ * @status - Result passed back from the secondary CPU to
> > >>+ *           indicate failure.
> > >>   */
> > >>  struct secondary_data {
> > >>  	void *stack;
> > >>-};
> > >>+	unsigned long status;
> > >>+} ____cacheline_aligned;
> > >
> > >Why is this necessary?
> > 
> > That was based on a suggestion from Mark Rutland here:
> > 
> >   https://lkml.org/lkml/2015/12/1/580
> 
> That thread is talking about the CWG, which is not the same thing as
> ____cacheline_aligned. Given that the architectural maximum for the CWG
> is 2K, we can probably get away with allocating the status field amongst
> the head.S text instead (which we know will be clean).
> 
> Since SMP boot is serialised, that should be sufficient, right?

Assuming you mean in .head.text (rather than .text), that should work
given that we don't currently free .head.text.

Mark.
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