linux-kernel - [PATCH v4 16/23] Documentation: userspace-api: iommufd: Update HW QUEUE

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Message-ID: <06b52408c31858e39a2fb557fd35f80db965f646.1746757630.git.nicolinc@nvidia.com>
Date: Thu, 8 May 2025 20:02:37 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: <jgg@...dia.com>, <kevin.tian@...el.com>, <corbet@....net>,
	<will@...nel.org>
CC: <bagasdotme@...il.com>, <robin.murphy@....com>, <joro@...tes.org>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<shuah@...nel.org>, <jsnitsel@...hat.com>, <nathan@...nel.org>,
	<peterz@...radead.org>, <yi.l.liu@...el.com>, <mshavit@...gle.com>,
	<praan@...gle.com>, <zhangzekun11@...wei.com>, <iommu@...ts.linux.dev>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>, <patches@...ts.linux.dev>,
	<mochs@...dia.com>, <alok.a.tiwari@...cle.com>, <vasant.hegde@....com>
Subject: [PATCH v4 16/23] Documentation: userspace-api: iommufd: Update HW QUEUE

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

Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 Documentation/userspace-api/iommufd.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

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:
 
-- 
2.43.0