From: Jason Gunthorpe <jgg@nvidia.com>
To: bpf@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
David Woodhouse <dwmw2@infradead.org>,
iommu@lists.linux.dev, Joerg Roedel <joro@8bytes.org>,
Kevin Tian <kevin.tian@intel.com>,
linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
llvm@lists.linux.dev, Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Miguel Ojeda <ojeda@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Shuah Khan <shuah@kernel.org>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Tom Rix <trix@redhat.com>, Will Deacon <will@kernel.org>
Cc: Alex Williamson <alex.williamson@redhat.com>,
Lu Baolu <baolu.lu@linux.intel.com>,
Chaitanya Kulkarni <chaitanyak@nvidia.com>,
Cornelia Huck <cohuck@redhat.com>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
David Gibson <david@gibson.dropbear.id.au>,
Eric Auger <eric.auger@redhat.com>,
Eric Farman <farman@linux.ibm.com>,
Jason Wang <jasowang@redhat.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>,
Joao Martins <joao.m.martins@oracle.com>,
kvm@vger.kernel.org, Matthew Rosato <mjrosato@linux.ibm.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Nicolin Chen <nicolinc@nvidia.com>,
Niklas Schnelle <schnelle@linux.ibm.com>,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
Yi Liu <yi.l.liu@intel.com>, Keqian Zhu <zhukeqian1@huawei.com>
Subject: [PATCH v4 04/17] iommufd: Document overview of iommufd
Date: Mon, 7 Nov 2022 20:48:57 -0400 [thread overview]
Message-ID: <4-v4-0de2f6c78ed0+9d1-iommufd_jgg@nvidia.com> (raw)
In-Reply-To: <0-v4-0de2f6c78ed0+9d1-iommufd_jgg@nvidia.com>
From: Kevin Tian <kevin.tian@intel.com>
Add iommufd into the documentation tree, and supply initial documentation.
Much of this is linked from code comments by kdoc.
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/iommufd.rst | 222 ++++++++++++++++++++++++
2 files changed, 223 insertions(+)
create mode 100644 Documentation/userspace-api/iommufd.rst
diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index c78da9ce0ec44e..f16337bdb8520f 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -25,6 +25,7 @@ place where this information is gathered.
ebpf/index
ioctl/index
iommu
+ iommufd
media/index
netlink/index
sysfs-platform_profile
diff --git a/Documentation/userspace-api/iommufd.rst b/Documentation/userspace-api/iommufd.rst
new file mode 100644
index 00000000000000..64a135f3055adc
--- /dev/null
+++ b/Documentation/userspace-api/iommufd.rst
@@ -0,0 +1,222 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+=======
+IOMMUFD
+=======
+
+:Author: Jason Gunthorpe
+:Author: Kevin Tian
+
+Overview
+========
+
+IOMMUFD is the user API to control the IOMMU subsystem as it relates to managing
+IO page tables from userspace using file descriptors. It intends to be general
+and consumable by any driver that wants to expose DMA to userspace. These
+drivers are eventually expected to deprecate any internal IOMMU logic if exists
+(e.g. vfio_iommu_type1.c).
+
+At minimum iommufd provides universal support of managing I/O address spaces and
+I/O page tables for all IOMMUs, with room in the design to add non-generic
+features to cater to specific hardware functionality.
+
+In this context the capital letter (IOMMUFD) refers to the subsystem while the
+small letter (iommufd) refers to the file descriptors created via /dev/iommu for
+use by userspace.
+
+Key Concepts
+============
+
+User Visible Objects
+--------------------
+
+Following IOMMUFD objects are exposed to userspace:
+
+- IOMMUFD_OBJ_IOAS, representing an I/O address space (IOAS), allowing map/unmap
+ of user space memory into ranges of I/O Virtual Address (IOVA).
+
+ The IOAS is a functional replacement for the VFIO container, and like the VFIO
+ container it copies an IOVA map to a list of iommu_domains held within it.
+
+- IOMMUFD_OBJ_DEVICE, representing a device that is bound to iommufd by an
+ external driver.
+
+- IOMMUFD_OBJ_HW_PAGETABLE, representing an actual hardware I/O page table
+ (i.e. a single struct iommu_domain) managed by the iommu driver.
+
+ The IOAS has a list of HW_PAGETABLES that share the same IOVA mapping and
+ it will synchronize its mapping with each member HW_PAGETABLE.
+
+All user-visible objects are destroyed via the IOMMU_DESTROY uAPI.
+
+The diagram below shows relationship between user-visible objects and kernel
+datastructures (external to iommufd), with numbers referred to operations
+creating the objects and links::
+
+ _________________________________________________________
+ | iommufd |
+ | [1] |
+ | _________________ |
+ | | | |
+ | | | |
+ | | | |
+ | | | |
+ | | | |
+ | | | |
+ | | | [3] [2] |
+ | | | ____________ __________ |
+ | | IOAS |<--| |<------| | |
+ | | | |HW_PAGETABLE| | DEVICE | |
+ | | | |____________| |__________| |
+ | | | | | |
+ | | | | | |
+ | | | | | |
+ | | | | | |
+ | | | | | |
+ | |_________________| | | |
+ | | | | |
+ |_________|___________________|___________________|_______|
+ | | |
+ | _____v______ _______v_____
+ | PFN storage | | | |
+ |------------>|iommu_domain| |struct device|
+ |____________| |_____________|
+
+1. IOMMUFD_OBJ_IOAS is created via the IOMMU_IOAS_ALLOC uAPI. An iommufd can
+ hold multiple IOAS objects. IOAS is the most generic object and does not
+ expose interfaces that are specific to single IOMMU drivers. All operations
+ on the IOAS must operate equally on each of the iommu_domains inside of it.
+
+2. IOMMUFD_OBJ_DEVICE is created when an external driver calls the IOMMUFD kAPI
+ to bind a device to an iommufd. The driver is expected to implement proper a
+ set of ioctls to allow userspace to initiate the binding operation.
+ Successful completion of this operation establishes the desired DMA ownership
+ over the device. The driver must also set the driver_managed_dma flag and
+ must not touch the device until this operation succeeds.
+
+3. IOMMUFD_OBJ_HW_PAGETABLE is created when an external driver calls the IOMMUFD
+ kAPI to attach a bound device to an IOAS. Similarly the external driver uAPI
+ allows userspace to initiate the attaching operation. If a compatible
+ pagetable already exists then it is reused for the attachment. Otherwise a
+ new pagetable object and iommu_domain is created. Successful completion of
+ this operation sets up the linkages among IOAS, device and iommu_domain. Once
+ this completes the device could do DMA.
+
+ Every iommu_domain inside the IOAS is also represented to userspace as a
+ HW_PAGETABLE object.
+
+ .. note::
+
+ Future IOMMUFD updates will provide an API to create and manipulate the
+ HW_PAGETABLE directly.
+
+A device can only bind to an iommufd due to DMA ownership claim and attach to at
+most one IOAS object (no support of PASID yet).
+
+Currently only PCI device is allowed to use IOMMUFD.
+
+Kernel Datastructure
+--------------------
+
+User visible objects are backed by following datastructures:
+
+- iommufd_ioas for IOMMUFD_OBJ_IOAS.
+- iommufd_device for IOMMUFD_OBJ_DEVICE.
+- iommufd_hw_pagetable for IOMMUFD_OBJ_HW_PAGETABLE.
+
+Several terminologies when looking at these datastructures:
+
+- Automatic domain - refers to an iommu domain created automatically when
+ attaching a device to an IOAS object. This is compatible to the semantics of
+ VFIO type1.
+
+- Manual domain - refers to an iommu domain designated by the user as the
+ target pagetable to be attached to by a device. Though currently there are
+ no uAPIs to directly create such domain, the datastructure and algorithms
+ are ready for handling that use case.
+
+- In-kernel user - refers to something like a VFIO mdev that is using the
+ IOMMUFD access interface to access the IOAS. This starts by creating an
+ iommufd_access object that is similar to the domain binding a physical device
+ would do. The access object will then allow converting IOVA ranges into struct
+ page * lists, or doing direct read/write to an IOVA.
+
+iommufd_ioas serves as the metadata datastructure to manage how IOVA ranges are
+mapped to memory pages, composed of:
+
+- struct io_pagetable holding the IOVA map
+- struct iopt_areas representing populated portions of IOVA
+- struct iopt_pages representing the storage of PFNs
+- struct iommu_domain representing the IO page table in the IOMMU
+- struct iopt_pages_access representing in-kernel users of PFNs
+- struct xarray pinned_pfns holding a list of pages pinned by in-kernel users
+
+Each iopt_pages represents a logical linear array of full PFNs. The PFNs are
+ultimately derived from userspave VAs via an mm_struct. Once they have been
+pinned the PFN is stored in IOPTEs of an iommu_domain or inside the pinned_pages
+xarray if they have been pinned through an iommufd_access.
+
+PFN have to be copied between all combinations of storage locations, depending
+on what domains are present and what kinds of in-kernel "software access" users
+exists. The mechanism ensures that a page is pinned only once.
+
+An io_pagetable is composed of iopt_areas pointing at iopt_pages, along with a
+list of iommu_domains that mirror the IOVA to PFN map.
+
+Multiple io_pagetable-s, through their iopt_area-s, can share a single
+iopt_pages which avoids multi-pinning and double accounting of page
+consumption.
+
+iommufd_ioas is sharable between subsystems, e.g. VFIO and VDPA, as long as
+devices managed by different subsystems are bound to a same iommufd.
+
+IOMMUFD User API
+================
+
+.. kernel-doc:: include/uapi/linux/iommufd.h
+
+IOMMUFD Kernel API
+==================
+
+The IOMMUFD kAPI is device-centric with group-related tricks managed behind the
+scene. This allows the external drivers calling such kAPI to implement a simple
+device-centric uAPI for connecting its device to an iommufd, instead of
+explicitly imposing the group semantics in its uAPI as VFIO does.
+
+.. kernel-doc:: drivers/iommu/iommufd/device.c
+ :export:
+
+VFIO and IOMMUFD
+----------------
+
+Connecting a VFIO device to iommufd can be done in two ways.
+
+First is a VFIO compatible way by directly implementing the /dev/vfio/vfio
+container IOCTLs by mapping them into io_pagetable operations. Doing so allows
+the use of iommufd in legacy VFIO applications by symlinking /dev/vfio/vfio to
+/dev/iommufd or extending VFIO to SET_CONTAINER using an iommufd instead of a
+container fd.
+
+The second approach directly extends VFIO to support a new set of device-centric
+user API based on aforementioned IOMMUFD kernel API. It requires userspace
+change but better matches the IOMMUFD API semantics and easier to support new
+iommufd features when comparing it to the first approach.
+
+Currently both approaches are still work-in-progress.
+
+There are still a few gaps to be resolved to catch up with VFIO type1, as
+documented in iommufd_vfio_check_extension().
+
+Future TODOs
+============
+
+Currently IOMMUFD supports only kernel-managed I/O page table, similar to VFIO
+type1. New features on the radar include:
+
+ - Binding iommu_domain's to PASID/SSID
+ - Userspace page tables, for ARM, x86 and S390
+ - Kernel bypass'd invalidation of user page tables
+ - Re-use of the KVM page table in the IOMMU
+ - Dirty page tracking in the IOMMU
+ - Runtime Increase/Decrease of IOPTE size
+ - PRI support with faults resolved in userspace
--
2.38.1
next prev parent reply other threads:[~2022-11-08 0:49 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-08 0:48 [PATCH v4 00/17] IOMMUFD Generic interface Jason Gunthorpe
2022-11-08 0:48 ` [PATCH v4 01/17] iommu: Add IOMMU_CAP_ENFORCE_CACHE_COHERENCY Jason Gunthorpe
2022-11-08 0:48 ` [PATCH v4 02/17] iommu: Add device-centric DMA ownership interfaces Jason Gunthorpe
2022-11-11 5:37 ` Tian, Kevin
2022-11-14 16:44 ` Jason Gunthorpe
2022-11-14 13:33 ` Eric Auger
2022-11-14 16:58 ` Jason Gunthorpe
2022-11-08 0:48 ` [PATCH v4 03/17] interval-tree: Add a utility to iterate over spans in an interval tree Jason Gunthorpe
2022-11-15 14:14 ` Eric Auger
2022-11-15 16:44 ` Jason Gunthorpe
2022-11-08 0:48 ` Jason Gunthorpe [this message]
2022-11-08 3:45 ` [PATCH v4 04/17] iommufd: Document overview of iommufd Bagas Sanjaya
2022-11-08 17:10 ` [PATCH v4 4/17] " Jason Gunthorpe
2022-11-11 5:59 ` Tian, Kevin
2022-11-14 15:14 ` Jason Gunthorpe
2022-11-10 9:30 ` [PATCH v4 04/17] " Bagas Sanjaya
2022-11-10 14:49 ` Jonathan Corbet
2022-11-10 14:54 ` Jason Gunthorpe
2022-11-10 15:10 ` Jonathan Corbet
2022-11-10 15:23 ` Jason Gunthorpe
2022-11-10 15:28 ` Jonathan Corbet
2022-11-10 15:29 ` Jason Gunthorpe
2022-11-10 15:52 ` Jonathan Corbet
2022-11-10 16:54 ` Jason Gunthorpe
2022-11-11 1:46 ` Bagas Sanjaya
2022-11-14 20:50 ` Eric Auger
2022-11-15 0:52 ` Jason Gunthorpe
2022-11-08 0:48 ` [PATCH v4 05/17] iommufd: File descriptor, context, kconfig and makefiles Jason Gunthorpe
2022-11-11 6:07 ` Tian, Kevin
2022-11-08 0:48 ` [PATCH v4 06/17] kernel/user: Allow user::locked_vm to be usable for iommufd Jason Gunthorpe
2022-11-08 0:49 ` [PATCH v4 07/17] iommufd: PFN handling for iopt_pages Jason Gunthorpe
2022-11-11 9:56 ` Tian, Kevin
2022-11-14 17:20 ` Jason Gunthorpe
2022-11-11 11:09 ` Tian, Kevin
2022-11-14 17:24 ` Jason Gunthorpe
2022-11-15 2:59 ` Tian, Kevin
2022-11-08 0:49 ` [PATCH v4 08/17] iommufd: Algorithms for PFN storage Jason Gunthorpe
2022-11-14 5:50 ` Tian, Kevin
2022-11-14 18:02 ` Jason Gunthorpe
2022-11-15 3:06 ` Tian, Kevin
2022-11-15 14:49 ` Jason Gunthorpe
2022-11-14 19:19 ` [PATCH v4 8/17] " Jason Gunthorpe
2022-11-08 0:49 ` [PATCH v4 09/17] iommufd: Data structure to provide IOVA to PFN mapping Jason Gunthorpe
2022-11-14 7:28 ` Tian, Kevin
2022-11-14 18:43 ` Jason Gunthorpe
2022-11-15 3:13 ` Tian, Kevin
2022-11-15 15:05 ` Jason Gunthorpe
2022-11-16 0:09 ` Tian, Kevin
2022-11-16 0:32 ` Jason Gunthorpe
2022-11-16 2:30 ` Tian, Kevin
2022-11-08 0:49 ` [PATCH v4 10/17] iommufd: IOCTLs for the io_pagetable Jason Gunthorpe
2022-11-08 13:27 ` Bagas Sanjaya
2022-11-08 17:01 ` Jason Gunthorpe
2022-11-14 7:46 ` Tian, Kevin
2022-11-08 0:49 ` [PATCH v4 11/17] iommufd: Add a HW pagetable object Jason Gunthorpe
2022-11-08 0:49 ` [PATCH v4 12/17] iommufd: Add kAPI toward external drivers for physical devices Jason Gunthorpe
2022-11-08 14:34 ` Yi Liu
2022-11-08 17:57 ` Jason Gunthorpe
2022-11-14 7:59 ` Tian, Kevin
2022-11-08 0:49 ` [PATCH v4 13/17] iommufd: Add kAPI toward external drivers for kernel access Jason Gunthorpe
2022-11-14 8:25 ` Tian, Kevin
2022-11-14 19:05 ` Jason Gunthorpe
2022-11-08 0:49 ` [PATCH v4 14/17] iommufd: vfio container FD ioctl compatibility Jason Gunthorpe
2022-11-08 0:49 ` [PATCH v4 16/17] iommufd: Add some fault injection points Jason Gunthorpe
2022-11-08 7:25 ` Nicolin Chen
2022-11-08 12:37 ` Jason Gunthorpe
2022-11-08 0:49 ` [PATCH v4 17/17] iommufd: Add additional invariant assertions Jason Gunthorpe
[not found] ` <15-v4-0de2f6c78ed0+9d1-iommufd_jgg@nvidia.com>
2022-11-08 1:01 ` [PATCH v4 15/17] iommufd: Add a selftest Jason Gunthorpe
2022-11-08 5:48 ` Nicolin Chen
2022-11-08 13:27 ` Jason Gunthorpe
2022-11-09 23:51 ` Matthew Rosato
2022-11-11 15:51 ` [PATCH v4 00/17] IOMMUFD Generic interface Shameerali Kolothum Thodi
2022-11-12 12:44 ` Yi Liu
2023-01-10 11:35 ` Shameerali Kolothum Thodi
2023-01-10 13:49 ` Jason Gunthorpe
2023-01-10 15:16 ` Joao Martins
2023-01-10 15:18 ` Jason Gunthorpe
2023-01-10 15:30 ` Shameerali Kolothum Thodi
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