On Wed, Jun 21, 2023 at 06:02:21AM +0000, Tian, Kevin wrote: > > > My understanding of ARM SMMU is that from host p.o.v. the CD is the > > > S1 in the nested configuration. 'identity' is one configuration in the CD > > > then it's in the business of nesting. > > > > I think it is the same. A CD doesn't come into the picture until the > > guest installs a CD pointing STE. Until that time the S2 is being used > > as identity. > > > > It sounds like the same basic flow. > > After a CD table is installed in a STE I assume the SMMU still allows to > configure an individual CD entry as identity? e.g. while vSVA is enabled > on a device the guest can continue to keep CD#0 as identity when the > default domain of the device is set as 'passthrough'. In this case the > IOAS still needs to gain reserved regions even though S2 is not directly > attached from host p.o.v. In any nesting configuration the hypervisor cannot directly restrict what IOVA the guest will use. The VM could make a normal nest and try to use unusable IOVA. Identity is not really special. The VMM should construct the guest memory map so that an identity iommu_domain can meet the reserved requirements - it needs to do this anyhow for the initial boot part. It shouuld try to forward the reserved regions to the guest via ACPI/etc. Being able to explicitly load reserved regions into an IOAS seems like a useful way to help construct this. Jason
