Re: [PATCH] iommu/arm-smmu-v3: Add HAFT support for SVA

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Jul 22, 2026 at 11:20:48PM +0100, Will Deacon wrote:

> > We might block traffic in the process of _explicitly blocking traffic_!?
> > Whoop-de-do, surely?
> 
> Hmm. I have very vague memories that there were some virtualisation (?)
> cases where Jason and Nicolin cared about the type of event that would
> be generated by concurrent DMA (e.g. bad CD vs translation fault) but
> maybe I'm misremembering.

Yeah, it is actually important for that special SVA mm drop/release
case. We need to write a CD that blocks walking but always generates
translation fault.

I'm away from my computer right now, but if sashiko is saying that the
SVA flow that uses EPD generates a racy bad CD then that is a bug that
needs to be fixed. Possibly by ignoring HAFT in the used calculation
for the EPD cases.

We should also try to have a kunit to cover that specific mm drop flow
in the SVA code.

Jason