[PATCH v9 19/27] 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 | 100 +++++++++++++++++++++++
 2 files changed, 101 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 45adbbc311db..b204b85e86db 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..62513af09cbf
--- /dev/null
+++ b/Documentation/virt/gunyah/vm-manager.rst
@@ -0,0 +1,100 @@
+.. 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 non-proxy
+scheduled Linux-like virtual machines.
+
+Except for some basic information about the location of initial binaries,
+most of the configuration about a Gunyah virtual machine is described in the
+VM's devicetree. The devicetree is generated by userspace. Interacting with the
+virtual machine is still done via the kernel and VM configuration requires some
+of the corresponding functionality to be set up in the kernel. For instance,
+sharing userspace memory with a VM is done via the GH_VM_SET_USER_MEM_REGION
+ioctl. The VM itself is configured to use the memory region via the
+devicetree.
+
+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.
+
+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 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 must
+be configured 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.
+
+To delete a memory region, call GH_VM_SET_USER_MEM_REGION with label set to the
+desired region and memory_size set to 0.
+
+The flags field of gh_userspace_memory_region accepts 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 VM.
-- 
2.39.0