Re: [PATCH v3 10/10] xen/arm: Enable errata for secondary CPU on hotplug after the boot

From: Dario Faggioli <dfaggioli@suse.com>
To: Julien Grall <julien.grall@arm.com>,
	Mirela Simonovic <mirela.simonovic@aggios.com>
Cc: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Davorin Mista <dm@aggios.com>,
	Xen Devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v3 10/10] xen/arm: Enable errata for secondary CPU on hotplug after the boot
Date: Thu, 10 May 2018 18:21:57 +0200	[thread overview]
Message-ID: <7eb8af10b99b61720ecd9ff273b38ec1e4ae163d.camel@suse.com> (raw)
In-Reply-To: <16d143e7-9edc-830d-8688-74839cb11583@arm.com>


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On Thu, 2018-05-10 at 17:02 +0100, Julien Grall wrote:
> On 10/05/18 16:49, Mirela Simonovic wrote:
> > Regardless of the fact that the notifier returns an error or not, I
> > believe it would be good and safe to set priority and document that
> > priority zero would cause racing issue in the scenario I debugged
> > today. I'm pretty sure that this discussion would be forgotten soon
> > and it really should be documented in code/comment.
> > 
> > In emails above I assumed we'll stop the erroneous CPU. I didn't
> > have
> > a chance to try returning an error until few minutes ago.
> > I tried returning an error from the notifier now and the whole
> > system
> > fails. You realized according to the answer below that this is
> > going
> > to happen.
> 
> I was aware about it since the beginning. The whole point of the 
> conversation was we should avoid to take the decision at the lower
> level 
> and let the upper layer decide what to do.
> 
This makes sense to me.

> > I would rather stop CPU because changing notify_cpu_starting
> > affects
> > x86 as well, I cannot dig into that and it would be really to much
> > for
> > this series. Since you're fine with stopping cpu as well, please
> > lets
> > do that instead of escalating this to who knows where :)
> 
> Also, while I suggest that it could be replaced by stop_cpu() in the 
> common code, I also suggested that notifier_cpu_starting() could
> return 
> an error then the architecture specific code can decide what to do.
> 
> On x86 it would still be a BUG_ON(notifier_cpu_starting()). On Arm
> we 
> can decide what to do. But it is not part of that discussion here.
> 
As just saind in the other email, I don't think this is all it's
necessary to enable CPU_STARTING to fail.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Software Engineer @ SUSE https://www.suse.com/

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