> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Tuesday, June 6, 2023 10:18 PM > > > > > It's not necessarily to add reserved regions to the IOAS of the parent > > > > hwpt since the device doesn't access that address space after it's > > > > attached to stage-1. The parent is used only for address translation > > > > in the iommu side. > > > > > > But if we don't put them in the IOAS of the parent there is no way for > > > userspace to learn what they are to forward to the VM ? > > > > emmm I wonder whether that is the right interface to report > > per-device reserved regions. > > The iommu driver needs to report different reserved regions for the S1 > and S2 iommu_domains, I can see the difference between RID and RID+PASID, but not sure whether it's a actual requirement regarding to attached domain. e.g. if only talking about RID then the same set of reserved regions should be reported for both S1 attach and S2 attach. > and the IOAS should only get the reserved regions for the S2. > > Currently the API has no way to report per-domain reserved regions and > that is possibly OK for now. The S2 really doesn't have reserved > regions beyond the domain aperture. > > So an ioctl to directly query the reserved regions for a dev_id makes > sense. Or more specifically query the reserved regions for RID-based access. Ideally for PASID there is no reserved region otherwise SVA won't work. 😊 > > > > Since we expect the parent IOAS to be usable in an identity mode I > > > think they should be added, at least I can't see a reason not to add > > > them. > > > > this is a good point. > > But it mixes things > > The S2 doesn't have reserved ranges restrictions, we always have some > model of a S1, even for identity mode, that would carry the reserved > ranges. > > > With that it makes more sense to make it a vendor specific choice. > > It isn't vendor specific, the ranges come from the domain that is > attached to the IOAS, and we simply don't import ranges for a S2 > domain. > With above I think the ranges are static per device. When talking about RID-based nesting alone, ARM needs to add reserved regions to the parent IOAS as identity is a valid S1 mode in nesting. But for Intel RID nesting excludes identity (which becomes a direct attach to S2) so the reserved regions apply to S1 instead of the parent IOAS.
