linux-kernel - Re: [PATCH v2 0/5] Initial support of Trusted Foundations on Tegra30

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Date:   Wed, 04 Jul 2018 14:25:11 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>
Subject: Re: [PATCH v2 0/5] Initial support of Trusted Foundations on Tegra30

On Monday, 2 July 2018 21:53:08 MSK Peter Geis wrote:
> On 07/02/2018 10:48 AM, Dmitry Osipenko wrote:
> > On Friday, 29 June 2018 22:37:02 MSK Peter Geis wrote:
> >> Good Afternoon,
> >> 
> >> I have tested these patches on the Ouya T3 device.
> >> They work great to enable the L2 cache controller, however they do not
> >> respect explicitly disabling the L2 cache controller via the kernel
> >> config nor device tree.
> >> 
> >> With CONFIG_CACHE_L2X0 disabled, but CONFIG_TRUSTED_FOUNDATIONS enabled,
> >> the L2 cache controller is silently enabled and allows all four cores to
> >> boot.
> > 
> > I don't see how cache could be enabled with CONFIG_CACHE_L2X0 disabled,
> > there is no code to do that. Could you elaborate please?
> > 
> > Secondary cores do not depend on the cache state, disabled cache shouldn't
> > prevent them to boot.
> 
> On the untouched mainline kernel running on a Trusted Foundations T3
> device, I observed the following indications:
> With the L2 cache controller enabled, all four processor cores were
> enabled, but it would immediately panic for writing to a secure register
> from insecure mode.
> With the L2 cache controller disabled, only the boot core is detected,
> but it successfully boots.
> This is the issue that I inquired originally to you about.
> 
> With your patch running on the same device, the following is observed:
> With the L2 controller enabled, all four cores are active, and the cache
> controller appears to function.
> With the L2 controller disabled, but trusted foundations enabled, the L2
> controller enabled kernel message is missing, however all four cores
> still enable.
> 

This is the correct behaviour.

> After looking through the code a little more deeply, I see you modified
> the reset handler for handling offline cores.
> I am wondering if you fixed an additional issue inadvertently.
> 

CPU will fail to boot if it tries to apply erratas via accessing the secure 
registers. I've changed the reset handler to skip erratas on T20/30 if trusted 
foundations present, see "Don't apply CPU erratas in insecure mode" patch. 
This is an intentional change.

> The reason I discovered this is I am working with kexec as a bootloader.
> On a device without trusted foundations, kexec works without issue.
> On a device with trusted foundations and your patch, I found that
> disabling the l2 cache controller and trusted foundations allow kexec to
> occur.
> I haven't tried an either/or scenario, though now you have me thinking I
> should.
> 

Secondary cores are dying in the reset handler in a case of disabled L2 + 
disabled TF. Looks like there is something wrong in regards to stopping 
secondary CPU cores / flushing CPU caches, the suspend-resume isn't working 
right now because of it and likely that kexec is suffering from the same 
issue.

> >> One must also disable CONFIG_TRUSTED_FOUNDATIONS to stop the L2 cache
> >> controller from spinning up.
> >> 
> >> Tested-by: Peter Geis <pgwipeout@...il.com>

Thanks for testing!