On Thu, Jul 10, 2014 at 05:14:05PM +0100, Alex Williamson wrote: > On Thu, 2014-07-10 at 16:45 +0100, Will Deacon wrote: > > On Thu, Jul 10, 2014 at 04:38:18PM +0100, Alex Williamson wrote: > > > On Thu, 2014-07-10 at 12:34 +0100, Will Deacon wrote: > > > > Do you think that returning something like -EOPNOTSUPP from an attach is > > > > sufficient for userspace to figure out what's gone wrong? > > > > > > It seems like this would all be a little easier if we had some sort of > > > bus_type iterator, then when we want to see if nesting is supported we'd > > > iterate the bus_types, test iommu_present(), iommu_domain_alloc(), > > > iommu_domain_set_attr(), iommu_domain_free(). We'd only allow a nesting > > > domain to be set if the IOMMU driver for at least one bus_type supports > > > it. Then I think enforcing it would be a little more obvious to > > > userspace. There is a bus_kset, but we'd need an iterator or at least > > > to enable find_bus() and have type1 walk a list of bus names known to > > > possibly support nesting (uglier, but functional). Thanks, > > > > That would work fine if we only had one IOMMU instance per bus. The problem > > is, the ARM SMMU driver (at least) can handle multiple SMMU instances on a > > single bus, only some of which may be capable of nesting. Until we've done > > an attach, it's impossible to know what the capabilities are (since the > > attach is what binds the domain to a physical IOMMU). > > > > So you'd actually need to iterate the bus_type, test iommu_present(), > > iommu_domain_alloc(), iommu_domain_attach(), iommu_domain_free(). The > > attach, of course, then requires devices which means you ultimately end up > > rolling VFIO_SET_IOMMU and VFIO_SET_CONTAINER into a single operation. I > > don't think that helps the group abstraction much! > > I don't really see how that diminishes the value. It still means that > it's only possible to set the IOMMU type of a container to nesting if > it's possible to support a nesting IOMMU. The user would get an error > trying to attach any group to the container that can't be supported as > nesting, whether that's behind the wrong bus_type or behind the wrong > IOMMU in the correct bus_type. The iommu-sysfs extensions that recently > went into the iommu next branch would help to expose this kind of > information to the user. > > It seems like an improvement versus statically advertising support for > something that actually cannot be enabled. Thanks,
Ok, I suppose it's an improvement. Given that we don't have a bus_type iterator, would you object if I only do this for the pci_bus_type for now (i.e. the only bus that's VFIO currently supports). Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
