On Wed, Jun 02, 2021 at 01:16:48PM -0300, Jason Gunthorpe wrote: > On Wed, Jun 02, 2021 at 04:32:27PM +1000, David Gibson wrote: > > > I agree with Jean-Philippe - at the very least erasing this > > > information needs a major rational - but I don't really see why it > > > must be erased? The HW reports the originating device, is it just a > > > matter of labeling the devices attached to the /dev/ioasid FD so it > > > can be reported to userspace? > > > > HW reports the originating device as far as it knows. In many cases > > where you have multiple devices in an IOMMU group, it's because > > although they're treated as separate devices at the kernel level, they > > have the same RID at the HW level. Which means a RID for something in > > the right group is the closest you can count on supplying. > > Granted there may be cases where exact fidelity is not possible, but > that doesn't excuse eliminating fedelity where it does exist.. > > > > If there are no hypervisor traps (does this exist?) then there is no > > > way to involve the hypervisor here and the child IOASID should simply > > > be a pointer to the guest's data structure that describes binding. In > > > this case that IOASID should claim all PASIDs when bound to a > > > RID. > > > > And in that case I think we should call that object something other > > than an IOASID, since it represents multiple address spaces. > > Maybe.. It is certainly a special case. > > We can still consider it a single "address space" from the IOMMU > perspective. What has happened is that the address table is not just a > 64 bit IOVA, but an extended ~80 bit IOVA formed by "PASID, IOVA". True. This does complexify how we represent what IOVA ranges are valid, though. I'll bet you most implementations don't actually implement a full 64-bit IOVA, which means we effectively have a large number of windows from (0..max IOVA) for each valid pasid. This adds another reason I don't think my concept of IOVA windows is just a power specific thing. > If we are already going in the direction of having the IOASID specify > the page table format and other details, specifying that the page > tabnle format is the 80 bit "PASID, IOVA" format is a fairly small > step. Well, rather I think userspace needs to request what page table format it wants and the kernel tells it whether it can oblige or not. > I wouldn't twist things into knots to create a difference, but if it > is easy to do it wouldn't hurt either. > > Jason > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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