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[v5,19/29] Documentation: userspace-api: iommufd: Update HW QUEUE

Message ID 852461f70d6ff3bc1c3c25bd67d3598091dc80ce.1747537752.git.nicolinc@nvidia.com
State New
Headers show
Series iommufd: Add vIOMMU infrastructure (Part-4 HW QUEUE) | expand

Commit Message

Nicolin Chen May 18, 2025, 3:21 a.m. UTC 
With the introduction of the new object and its infrastructure, update the
doc to reflect that.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 Documentation/userspace-api/iommufd.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)
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Patch

diff --git a/Documentation/userspace-api/iommufd.rst b/Documentation/userspace-api/iommufd.rst
index b0df15865dec..03f7510384d2 100644
--- a/Documentation/userspace-api/iommufd.rst
+++ b/Documentation/userspace-api/iommufd.rst
@@ -124,6 +124,17 @@  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_HW_QUEUE, representing a hardware accelerated queue, as a subset
+  of IOMMU's virtualization features, for the IOMMU HW to directly read or write
+  the virtual queue memory owned by a guest OS. This HW-acceleration feature can
+  allow VM to work with the IOMMU HW directly without a VM Exit, so as to reduce
+  overhead from the hypercalls. Along with the HW QUEUE object, iommufd provides
+  user space an mmap interface for VMM to mmap a physical MMIO region from the
+  host physical address space to the guest physical address space, allowing the
+  guest OS to directly control the allocated HW QUEUE. Thus, when allocating a
+  HW QUEUE, the VMM must request a pair of mmap info (offset/length) and pass in
+  exactly to an mmap syscall via its offset and length arguments.
+
 All user-visible objects are destroyed via the IOMMU_DESTROY uAPI.
 
 The diagrams below show relationships between user-visible objects and kernel
@@ -270,6 +281,7 @@  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_hw_queue for IOMMUFD_OBJ_HW_QUEUE.
 
 Several terminologies when looking at these datastructures: