[PATCH v2 15/22] Documentation: userspace-api: iommufd: Update vCMDQ

Nicolin Chen
2025-04-26T05:59:31Z

With the introduction of the new object and its infrastructure, update the
doc to reflect that.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
Documentation/userspace-api/iommufd.rst | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/Documentation/userspace-api/iommufd.rst b/Documentation/userspace-api/iommufd.rst
index b0df15865dec..afca749652ee 100644
--- a/Documentation/userspace-api/iommufd.rst
+++ b/Documentation/userspace-api/iommufd.rst
@@ -124,6 +124,19 @@ Following IOMMUFD objects are exposed to userspace:
used to allocate a vEVENTQ. Each vIOMMU can support multiple types of vEVENTS,
but is confined to one vEVENTQ per vEVENTQ type.

+- IOMMUFD_OBJ_VCMDQ, representing a hardware queue as a subset of a vIOMMU's
+ virtualization feature for a VM to directly execute guest-issued commands to
+ invalidate HW cache entries holding the mappings or translations of a guest-
+ owned stage-1 page table. Along with this queue object, iommufd provides the
+ user space an mmap interface for VMM to mmap a physical MMIO region from the
+ host physical address space to a guest physical address space, to exclusively
+ control the allocated vCMDQ HW. Thus, when allocating a vCMDQ, the VMM must
+ request a pair of VMA info (vm_pgoff/size) for a later mmap call. The length
+ argument of an mmap call could be smaller than the given size for a paritial
+ mmap, but the given vm_pgoff (as the addr argument of the mmap call) should
+ never be offsetted, which also implies that the mmap will always start from
+ the beginning of the physical MMIO region.
+
All user-visible objects are destroyed via the IOMMU_DESTROY uAPI.

The diagrams below show relationships between user-visible objects and kernel
@@ -270,6 +283,7 @@ User visible objects are backed by following datastructures:
- iommufd_viommu for IOMMUFD_OBJ_VIOMMU.
- iommufd_vdevice for IOMMUFD_OBJ_VDEVICE.
- iommufd_veventq for IOMMUFD_OBJ_VEVENTQ.
+- iommufd_vcmdq for IOMMUFD_OBJ_VCMDQ.

Several terminologies when looking at these datastructures:

--
2.43.0