[PATCH v14 16/25] docs: gunyah: Document Gunyah VM Manager

[Elliot Berman]

Document the ioctls and usage of Gunyah VM Manager driver.

Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>
---
 Documentation/virt/gunyah/index.rst      |  1 +
 Documentation/virt/gunyah/vm-manager.rst | 83 ++++++++++++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 Documentation/virt/gunyah/vm-manager.rst

diff --git a/Documentation/virt/gunyah/index.rst b/Documentation/virt/gunyah/index.rst
index 74aa345e0a144..7058249825b16 100644
--- a/Documentation/virt/gunyah/index.rst
+++ b/Documentation/virt/gunyah/index.rst
@@ -7,6 +7,7 @@ Gunyah Hypervisor
 .. toctree::
    :maxdepth: 1
 
+   vm-manager
    message-queue
 
 Gunyah is a Type-1 hypervisor which is independent of any OS kernel, and runs in
diff --git a/Documentation/virt/gunyah/vm-manager.rst b/Documentation/virt/gunyah/vm-manager.rst
new file mode 100644
index 0000000000000..df0e1a8279bf5
--- /dev/null
+++ b/Documentation/virt/gunyah/vm-manager.rst
@@ -0,0 +1,83 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+Virtual Machine Manager
+=======================
+
+The Gunyah Virtual Machine Manager is a Linux driver to support launching
+virtual machines using Gunyah. It presently supports launching virtual machines
+scheduled by Gunyah's scheduler.
+
+Configuration of a Gunyah virtual machine is done via a devicetree. When the VM
+is launched, memory is provided by the host VM which contains the devictree.
+Gunyah reads the devicetree to configure the memory map and create resources
+such as vCPUs for the VM. Memory can be shared with the VM with
+`GH_VM_SET_USER_MEM_REGION`_. Userspace can interact with the resources in Linux
+by adding "functions" to the VM.
+
+Sample Userspace VMM
+====================
+
+A sample userspace VMM is included in samples/gunyah/ along with a minimal
+devicetree that can be used to launch a VM. To build this sample, enable
+CONFIG_SAMPLE_GUNYAH.
+
+IOCTLs and userspace VMM flows
+==============================
+
+The kernel exposes a char device interface at /dev/gunyah.
+
+To create a VM, use the `GH_CREATE_VM`_ ioctl. A successful call will return a
+"Gunyah VM" file descriptor.
+
+/dev/gunyah API Descriptions
+----------------------------
+
+GH_CREATE_VM
+~~~~~~~~~~~~
+
+Creates a Gunyah VM. The argument is reserved for future use and must be 0.
+A successful call will return a Gunyah VM file descriptor. See
+`Gunyah VM API Descriptions`_ for list of IOCTLs that can be made on this file
+file descriptor.
+
+Gunyah VM API Descriptions
+--------------------------
+
+GH_VM_SET_USER_MEM_REGION
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This ioctl allows the user to create or delete a memory parcel for a guest
+virtual machine. Each memory region is uniquely identified by a label;
+attempting to create two regions with the same label is not allowed. Labels are
+unique per virtual machine.
+
+While VMM is guest-agnostic and allows runtime addition of memory regions,
+Linux guest virtual machines do not support accepting memory regions at runtime.
+Thus, for Linux guests, memory regions should be provided before starting the VM
+and the VM must be configured via the devicetree to accept these at boot-up.
+
+The guest physical address is used by Linux kernel to check that the requested
+user regions do not overlap and to help find the corresponding memory region
+for calls like `GH_VM_SET_DTB_CONFIG`_. It must be page aligned.
+
+To add a memory region, call `GH_VM_SET_USER_MEM_REGION`_ with fields set as
+described above.
+
+.. kernel-doc:: include/uapi/linux/gunyah.h
+   :identifiers: gh_userspace_memory_region gh_mem_flags
+
+GH_VM_SET_DTB_CONFIG
+~~~~~~~~~~~~~~~~~~~~
+
+This ioctl sets the location of the VM's devicetree blob and is used by Gunyah
+Resource Manager to allocate resources. The guest physical memory must be part
+of the primary memory parcel provided to the VM prior to GH_VM_START.
+
+.. kernel-doc:: include/uapi/linux/gunyah.h
+   :identifiers: gh_vm_dtb_config
+
+GH_VM_START
+~~~~~~~~~~~
+
+This ioctl starts the VM.
-- 
2.40.0