Re: [PATCH 1/4] gpu: host1x: Enable Tegra186 syncpoint protection

[Mikko Perttunen]

On 08/19/2017 01:09 PM, Dmitry Osipenko wrote:
> On 19.08.2017 11:10, Mikko Perttunen wrote:
> [snip]
> > > > +    host1x_hw_syncpt_set_protection(host, true);
> > >
> > > Is it really okay to force the protection? Maybe protection should be enabled
> > > with a respect to CONFIG_TEGRA_HOST1X_FIREWALL? In that case we would have to
> > > avoid software jobs validation for Tegra124+.
> >
> > I don't quite get your comment. The hardware syncpt protection layer being
> > enabled should never hurt - it doesn't mess with any valid jobs. It's also only
> > on Tegra186 so I'm not sure where the Tegra124 comes from.
>
> Right, it's the gather filter on T124+, my bad. This raises several questions.
>
> 1) Why we have CONFIG_TEGRA_HOST1X_FIREWALL? Should it be always enforced or we
> actually want to be a bit more flexible and allow to disable it. Imagine that
> you are making a custom application and want to utilize channels in a different way.

I think it should be up to the user to decide whether they want the 
firewall or not. It's clearly the most useful on the older chips - 
especially Tegra20 due to lack of IOMMU. The performance penalty is too 
great to force it on always.

The programming model should always be considered the same - the rules 
of what you are allowed to do are the same whether the firewall, or any 
hardware-implemented protection features, are on or not.

> 2) Since syncpoint protection is a T186 feature, what about previous
> generations? Should we validate syncpoints in software for them? We have
> 'syncpoint validation' patch staged in grate's kernel
> https://github.com/grate-driver/linux/commit/c8b6c82173f2ee9fead23380e8330b8099e7d5e7
> (I'll start sending out this and other patches after a bit more thorough
> testing.) Improperly used syncpoints potentially could allow one program to
> damage others.

Yes, I think the firewall should have this feature for older 
generations. We could disable the check on Tegra186, as you point 
towards in question 4.

> 3) What exactly does gather filter? Could you list all the commands that it
> filters out, please?

According to the Tegra186 TRM (section 16.8.32), SETCLASS, SETSTRMID and 
EXTEND are filtered.

> 4) What about T30/T114 that do not have gather filter? Should we validate those
> commands for them in a software firewall?

Yes, the firewall should validate that.

> So maybe we should implement several layers of validation in the SW firewall.
> Like all layers for T20 (memory boundaries validation etc), software gather
> filter for T30/114 and software syncpoint validation for T30/114/124/210.

That seems like a good idea.

Thanks,
Mikko