On Thu, Jan 23, 2025 at 09:06:49AM +0000, Shameerali Kolothum Thodi wrote:
One confusion I have about the above text is, do we still plan to support the approach -1( Using RMR in Qemu)
Yes, it remains an option. The VMM would use the IOMMU_OPTION_SW_MSI_START/SIZE ioctls to tell the kernel where it wants to put the RMR region then it would send the RMR into the VM through ACPI.
The kernel side promises that the RMR region will have a consistent (but unpredictable!) layout of ITS pages (however many are required) within that RMR space, regardless of what devices/domain are attached.
I would like to start with patches up to #10 for this part as it solves two of the three problems here.
or you are just mentioning it here because it is still possible to make use of that. I think from previous discussions the argument was to adopt a more dedicated MSI pass-through model which I think is approach-2 here.
The basic flow of the pass through model is shown in the last two patches, it is not fully complete but is testable. It assumes a single ITS page. The VM would use IOMMU_OPTION_SW_MSI_START/SIZE to put the ITS page at the correct S2 location and then describe it in the ACPI as an ITS page not a RMR.
The VMM will capture the MSI writes and use VFIO_IRQ_SET_ACTION_PREPARE to convey the guests's S1 translation to the IRQ subsystem.
This missing peice is cleaning up the ITS mapping to allow for multiple ITS pages. I've imagined that kvm would someone give iommufd a FD that holds the specific ITS pages instead of the IOMMU_OPTION_SW_MSI_START/SIZE flow.
Jason