Re: [PATCH] PCI: revert "Enable PASID only when ACS RR & UF enabled on upstream path"

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Jan 11, 2023 at 03:07:36PM +0100, Christian König wrote:

>    Well no, we can perfectly fine enable this as we have done in the past.
>    What we can't do is rejecting it without driver specific knowledge,
>    because the hardware might still work correctly.

It is an interesting point that any device using PASID for SVA must
necessary also be doing ATS/PRI and thus must always be setting the
translated bit in their Mem TLPs

So, at least at this instant in the kernel we have no need for the ACS
check as everything is SVA.

This is forward looking where we are going to have non SVA uses of
PASIDs and we cannot guarantee translated TLPs.

Keep in mind this is pretty much an integrity problem, eg if I allow
iommufd to assign page tables to a PASID without PRI we can get bad
behaviors if the HW does not route properly.

So we are justified to be conservative here to prevent data corruption
in bad cases.

Jason