[PATCH v6 21/21] docs: gunyah: Document Gunyah VM Manager

[Elliot Berman <quic_eberman@quicinc.com>]

Document the ioctls and usage of Gunyah VM Manager driver.

Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
---
 Documentation/virt/gunyah/index.rst      |  1 +
 Documentation/virt/gunyah/vm-manager.rst | 94 ++++++++++++++++++++++++
 2 files changed, 95 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 fbadbdd24da7..9019a03b6f3e 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 000000000000..c232ba05de7e
--- /dev/null
+++ b/Documentation/virt/gunyah/vm-manager.rst
@@ -0,0 +1,94 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+Virtual Machine Manager
+=======================
+
+The Gunyah Virtual Machine Manager is a Linux driver to support launching virtual machines.
+
+Summary
+=======
+
+Gunyah VMM presently supports launching non-proxy scheduled Linux-like virtual machines.
+
+Sample Userspace VMM
+====================
+
+A sample userspace VMM is included in samples/gunyah/ along with a sample minimal devicetree
+that can be used to launch a Linux-like virtual machine under Gunyah. 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.
+
+Gunyah VM API Descriptions
+--------------------------
+
+GH_VM_SET_USER_MEM_REGION
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+  struct gh_userspace_memory_region {
+	__u32 label;
+	__u32 flags;
+	__u64 guest_phys_addr;
+	__u64 memory_size;
+	__u64 userspace_addr;
+  };
+
+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 memory regions with the same label is not allowed.
+
+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, memory regions should be provided before starting the VM and the VM
+configured to accept those memory regions at boot-up.
+
+The guest physical address is used by Linux to check the requested user regions
+do not overlap and to help find a corresponding memory region for calls like
+GH_VM_SET_DTB_CONFIG.
+
+To delete a memory region, call GH_VM_SET_USER_MEM_REGION with label set to the
+memory region of interest and memory_size set to 0.
+
+The flags field of gh_userspace_memory_region can set the following bits. All
+other bits must be 0 and are reserved for future use. The ioctl will return
+-EINVAL if an unsupported bit is detected.
+
+  - GH_MEM_ALLOW_READ/GH_MEM_ALLOW_WRITE/GH_MEM_ALLOW_EXEC sets read/write/exec permissions
+    for the guest, respectively.
+
+  - GH_MEM_LENT means that the memory will be unmapped from the host and be unaccessible by
+    the host while the guest has the region.
+
+GH_VM_SET_DTB_CONFIG
+~~~~~~~~~~~~~~~~~~~~
+
+::
+
+  struct gh_vm_dtb_config {
+	__u64 gpa;
+	__u64 size;
+  };
+
+This ioctl sets the location of the VM's devicetree blob and is used by Gunyah
+Resource Manager to allocate resources.
+
+GH_VM_START
+~~~~~~~~~~~
+
+This ioctl starts the virtual machine.
-- 
2.25.1