Re: [PATCH] iommu/arm-smmu-v3: Set GBPA to abort all transactions

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

On Thu, Apr 12, 2018 at 11:17:24AM +0100, Robin Murphy wrote:
> On 11/04/18 17:54, Marc Zyngier wrote:
> >On 11/04/18 16:58, Goel, Sameer wrote:
> >>On 3/28/2018 9:00 AM, Marc Zyngier wrote:
> >>>A tangential question: can we reliably detect that the SMMU already
> >>>has valid mappings, which would indicate that we're in a pretty bad
> >>>shape already by the time we set that bit? For all we know, memory
> >>>could have been corrupted long before we hit this point, and this
> >>>patch barely narrows the window of opportunity.
> >>
> >>:) Yes that is correct. This only covers the kdump scenario. Trying
> >>to get some reliability when booting up the crash kernel. The system
> >>is already in a bad state. I don't think that this will happen in a
> >>normal scenario. But please point me to the GICv3 change and I'll
> >>have a look.
> >
> >See this:
> >https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/tree/drivers/irqchip/irq-gic-v3-its.c?h=irq/irqchip-4.17&id=6eb486b66a3094cdcd68dc39c9df3a29d6a51dd5#n3407
> 
> The nearest equivalent to that is probably the top-level SMMUEN check that
> we already have (see the diff context above). To go beyond that you'd have
> to chase the old stream table pointer and scan the whole thing looking for
> valid contexts, then potentially walk page tables within those contexts to
> check for live translations if you really wanted to be sure. That would be a
> hell of a lot of work to do in the boot path.

Yeah, please don't waste time writing a patch to do that! ;)

Will