Hi Nicolin,
On 4/11/2025 12:07 PM, Nicolin Chen wrote:
The vIOMMU object is designed to represent a slice of an IOMMU HW for its virtualization features shared with or passed to user space (a VM mostly) in a way of HW acceleration. This extended the HWPT-based design for more advanced virtualization feature.
A vCMDQ introduced by this series as a part of the vIOMMU infrastructure represents a HW supported queue/buffer for VM to use exclusively, e.g.
- NVIDIA's virtual command queue
- AMD vIOMMU's command buffer
I assume we can pass multiple buffer details (like GPA, size) from guest to hypervisor. Is that correct understanding?
either of which is an IOMMU HW feature to directly load and execute cache invalidation commands issued by a guest kernel, to shoot down TLB entries that HW cached for guest-owned stage-1 page table entries. This is a big improvement since there is no VM Exit during an invalidation, compared to the traditional invalidation pathway by trapping a guest-own invalidation queue and forwarding those commands/requests to the host kernel that will eventually fill a HW-owned queue to execute those commands.
Thus, a vCMDQ object, as an initial use case, is all about a guest-owned HW command queue that VMM can allocate/configure depending on the request from a guest kernel. Introduce a new IOMMUFD_OBJ_VCMDQ and its allocator IOMMUFD_CMD_VCMDQ_ALLOC allowing VMM to forward the IOMMU-specific queue info, such as queue base address, size, and etc.
Meanwhile, a guest-owned command queue needs the kernel (a command queue
driver) to control the queue by reading/writing its consumer and producer indexes, which means the command queue HW allows the guest kernel to get a direct R/W access to those registers. Introduce an mmap infrastructure to the iommufd core so as to support pass through a piece of MMIO region from the host physical address space to the guest physical address space. The VMA info (vm_pgoff/size) used by an mmap must be pre-allocated during the IOMMUFD_CMD_VCMDQ_ALLOC and given those info to the user space as an output driver-data by the IOMMUFD_CMD_VCMDQ_ALLOC. So, this requires a driver-specific user data support by a vIOMMU object.
Nice! Thanks.
-Vasant