On Thu, Nov 07, 2024 at 12:37:59PM +1100, Alexey Kardashevskiy wrote:
- hwpt_paging = iommufd_get_hwpt_paging(ucmd, cmd->hwpt_id);
- if (IS_ERR(hwpt_paging)) {
rc = PTR_ERR(hwpt_paging);goto out_put_idev;- }
- if (!hwpt_paging->nest_parent) {
I am trying to use this for my so-called viommu which does not have this so this fails. My viommu is only visible to the VM via paravirt interface to populate sDTE (secure device table) so no viommu device in the guest or nested paging, nothing like this just yet.
The purpose of this is to define the translation underlying the viommu and the VM.
If I understand AMD CC HW correctly, you still need to have a translation to make the device work - so you should have a nest_parent.
For AMD the nest_parent is simply a v1 domain and, with what is in Joerg's tree the AMD driver can quickly be improved to support that allocation option.
Is there a writeup somewhere about possible uses of this IOMMU_HWPT_ALLOC_NEST_PARENT? I'd think one pass through device equals 1 IOAS, 1 HWPT, 1 domain, 1 viommu, even with guest visible vIOMMU but it is not the case, is it?
It is intended for HW like AMD that requires selecting a special page table format to be used on the hypervisor side. Ie select the v1 page table format.
btw is there a way to get a snapshot of all current objects in iommufd? They all use "dev_id" and not file descriptors so cannot look at /proc/><pid>/fd, and there is nothing in debugfs either.
Nothing has been done, a debugfs could be interesting
For my current hack, I can pass IOMMU_HWPT_ALLOC_NEST_PARENT to QEMU's iommufd_backend_alloc_hwpt() but it is... meh. Thanks,
This is what I'd expect, yes. Qemu should be allocating domains that are going to be used as part of advanced virtualization (viommu, nesting, etc) using NEST_PARENT, AMD driver should accept this and enforce the v1 format.
Jason