Re: [PATCH RFC 2/2] iommu/arm-smmu-v3: Bypass SID0 for NXP i.MX95

[Robin Murphy]

On 2024-10-15 4:31 pm, Jason Gunthorpe wrote:
> On Tue, Oct 15, 2024 at 04:13:13PM +0100, Robin Murphy wrote:
> > On 2024-10-15 1:47 pm, Jason Gunthorpe wrote:
> > > On Tue, Oct 15, 2024 at 08:13:28AM +0000, Pranjal Shrivastava wrote:
> > >
> > > > Umm.. this was specific for rmr not a generic thing. I'd suggest to
> > > > avoid meddling with the STEs directly for acheiving bypass. Playing
> > > > with the iommu domain type could be neater. Perhaps, modify the
> > > > ops->def_domain_type to return an appropriate domain?
> > >
> > > Yeah, that is the expected way, to force the def_domain_type to
> > > IDENTITY and refuse to attach a PAGING/BLOCKED domain.
> >
> > There is no domain, this is bypassing an arbitrary StreamID not associated
> > with any device.
>
> If the stream ID is going to flow traffic shouldn't it have a DT node
> for it? Something must be driving the DMA on this SID, and the kernel
> does need to know what that is in some way, even for basic security
> things like making sure VFIO doesn't get a hold of it :\

Exactly, hence this RFC is definitely not the right approach.

Thanks,
Robin.