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I assume this case can be > > > an exception since there's no point in allowing a device that has no > > > driver yet to access any reserved region? > > > > If require_direct is set then we have to disable this mechanism.. > > > > I'm not sure exactly what to do about this as the require_direct comes > > from the hypervisor in a CC VM and we probably don't want to give the > > hypervisor this kind of escape hatch. > > > > Perhaps we need to lock off to failure on CC VMs if this ever > > happens.. > > > > But baremetal should just keep working how it always worked in this > > case.. > > OK. I will put a note in the patch, since it would literally skip > any VM case at this moment. > > I just realized a corner case, as iommu_probe_device() may attach > the device to group->domain if it's set: > https://lore.kernel.org/all/9-v5-1b99ae392328+44574-iommu_err_unwind_jgg@nvidia.com/ > > I am not sure about the use case, but I assume we should skip the > blocking_domain as well in this case? > > Then, this makes the condition be: > + if (!dev->driver && !group->domain && !dev->iommu->require_direct) { > + ret = __iommu_group_alloc_blocking_domain(group); > + if (ret) > + goto err_remove_gdev; > + group->domain = group->blocking_domain; > + } Just to be clear this is some other project "DMA boot security" and IDK if we need to do it until the CC patches land for user space device binding policy, or someone seriously implements DRTM.. Jason