Suggested-by: Cédric Le Goater <c...@redhat.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
---
MAINTAINERS | 1 +
docs/devel/index-internals.rst | 1 +
docs/devel/vfio-iommufd.rst | 115 +++++++++++++++++++++++++++++++++
3 files changed, 117 insertions(+)
create mode 100644 docs/devel/vfio-iommufd.rst
diff --git a/MAINTAINERS b/MAINTAINERS
index d86ba56a49..07990456ed 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2175,6 +2175,7 @@ F: backends/iommufd.c
F: include/sysemu/iommufd.h
F: include/qemu/chardev_open.h
F: util/chardev_open.c
+F: docs/devel/vfio-iommufd.rst
vhost
M: Michael S. Tsirkin <m...@redhat.com>
diff --git a/docs/devel/index-internals.rst b/docs/devel/index-internals.rst
index 6f81df92bc..3def4a138b 100644
--- a/docs/devel/index-internals.rst
+++ b/docs/devel/index-internals.rst
@@ -18,5 +18,6 @@ Details about QEMU's various subsystems including how to add
features to them.
s390-dasd-ipl
tracing
vfio-migration
+ vfio-iommufd
writing-monitor-commands
virtio-backends
diff --git a/docs/devel/vfio-iommufd.rst b/docs/devel/vfio-iommufd.rst
new file mode 100644
index 0000000000..59804a7f26
--- /dev/null
+++ b/docs/devel/vfio-iommufd.rst
@@ -0,0 +1,115 @@
+===============================
+IOMMUFD BACKEND usage with VFIO
+===============================
+
+(Same meaning for backend/container/BE)
+
+With the introduction of iommufd, the Linux kernel provides a generic
+interface for user space drivers to propagate their DMA mappings to kernel
+for assigned devices. While the legacy kernel interface is group-centric,
+the new iommufd interface is device-centric, relying on device fd and iommufd.
+
+To support both interfaces in the QEMU VFIO device, introduce a base container
+to abstract the common part of VFIO legacy and iommufd container. So that the
+generic VFIO code can use either container.
+
+The base container implements generic functions such as memory_listener and
+address space management whereas the derived container implements callbacks
+specific to either legacy or iommufd. Each container has its own way to setup
+secure context and dma management interface. The below diagram shows how it
+looks like with both containers.
+
+ VFIO AddressSpace/Memory
+ +-------+ +----------+ +-----+ +-----+
+ | pci | | platform | | ap | | ccw |
+ +---+---+ +----+-----+ +--+--+ +--+--+ +----------------------+
+ | | | | | AddressSpace |
+ | | | | +------------+---------+
+ +---V-----------V-----------V--------V----+ /
+ | VFIOAddressSpace | <------------+
+ | | | MemoryListener
+ | VFIOContainerBase list |
+ +-------+----------------------------+----+
+ | |
+ | |
+ +-------V------+ +--------V----------+
+ | iommufd | | vfio legacy |
+ | container | | container |
+ +-------+------+ +--------+----------+
+ | |
+ | /dev/iommu | /dev/vfio/vfio
+ | /dev/vfio/devices/vfioX | /dev/vfio/$group_id
+Userspace | |
+============+============================+===========================
+Kernel | device fd |
+ +---------------+ | group/container fd
+ | (BIND_IOMMUFD | | (SET_CONTAINER/SET_IOMMU)
+ | ATTACH_IOAS) | | device fd
+ | | |
+ | +-------V------------V-----------------+
+ iommufd | | vfio |
+(map/unmap | +---------+--------------------+-------+
+ioas_copy) | | | map/unmap
+ | | |
+ +------V------+ +-----V------+ +------V--------+
+ | iommfd core | | device | | vfio iommu |
+ +-------------+ +------------+ +---------------+
+
+[Secure Context setup]
+- iommufd BE: uses device fd and iommufd to setup secure context
+ (bind_iommufd, attach_ioas)
+- vfio legacy BE: uses group fd and container fd to setup secure context
+ (set_container, set_iommu)
+
+[Device access]
+- iommufd BE: device fd is opened through /dev/vfio/devices/vfioX
+- vfio legacy BE: device fd is retrieved from group fd ioctl
+
+[DMA Mapping flow]
+1. VFIOAddressSpace receives MemoryRegion add/del via MemoryListener
+2. VFIO populates DMA map/unmap via the container BEs
+ *) iommufd BE: uses iommufd
+ *) vfio legacy BE: uses container fd
+
+
+Example configuration
+=====================
+
+Step 1: configure the host device
+---------------------------------
+
+It's exactly same as the VFIO device with legacy VFIO container.
+
+Step 2: configure QEMU
+----------------------
+
+Interactions with the /dev/iommu are abstracted by a new
+iommufd object (compiled in with the CONFIG_IOMMUFD option).
+
+Any QEMU device (e.g. VFIO device) wishing to use /dev/iommu must be
+linked with an iommufd object. It gets a new optional property named
+iommufd which allows to pass an iommufd object. Take vfio-pci device
+for example:
+
+ -object iommufd,id=iommufd0
+ -device vfio-pci,host=0000:02:00.0,iommufd=iommufd0
+
+Note the /dev/iommu and VFIO cdev can be externally opened by a
+management layer. In such a case the fd is passed, the fd supports
+a string naming the fd or a number, for example:
+
+ -object iommufd,id=iommufd0,fd=22
+ -device vfio-pci,iommufd=iommufd0,fd=23
+
+If the fd property is not passed, the fd is opened by QEMU.
+
+If no iommufd property is passed to the vfio-pci device, iommufd is
+not used and the user gets the behavior based on the legacy VFIO
+container:
+
+ -device vfio-pci,host=0000:02:00.0
+
+Supported platform
+==================
+
+Supports X86, ARM and S390X currently.
--
2.34.1
