> From: Jason Gunthorpe <j...@nvidia.com> > Sent: Thursday, May 18, 2023 10:57 PM > > On Thu, May 18, 2023 at 10:16:24AM -0400, Peter Xu wrote: > > > What you mentioned above makes sense to me from the POV that 1 > vIOMMU may > > not suffice, but that's at least totally new area to me because I never > > used >1 IOMMUs even bare metal (excluding the case where I'm aware > that > > e.g. a GPU could have its own IOMMU-like dma translator). > > Even x86 systems are multi-iommu, one iommu per physical CPU socket. > > I'm not sure how they model this though - Kevin do you know? Do we get > multiple iommu instances in Linux or is all the broadcasting of > invalidates and sharing of tables hidden? >
Yes Linux supports multiple iommu instances on x86 systems. Each iommu has its own configuration structures/caches and attached devices. No broadcasting. An ACPI table is used to describe the topology between IOMMUs and devices. If an iommu domain is attached to two devices behind two IOMMUs, separate iotlb invalidation commands are required when the domain mapping is changed.
