[PATCH v8 6/6] docs/nitro-enclave: Documentation for nitro-enclave machine type

[Dorjoy Chowdhury <dorjoychy111@gmail.com>]

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
---
 MAINTAINERS                        |  1 +
 docs/system/i386/nitro-enclave.rst | 78 ++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 docs/system/i386/nitro-enclave.rst

diff --git a/MAINTAINERS b/MAINTAINERS
index f78a7cca06..a857e056e1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1827,6 +1827,7 @@ F: hw/core/eif.c
 F: hw/core/eif.h
 F: hw/i386/nitro_enclave.c
 F: include/hw/i386/nitro_enclave.h
+F: docs/system/i386/nitro-enclave.rst
 
 Machine core
 M: Eduardo Habkost <eduardo@habkost.net>
diff --git a/docs/system/i386/nitro-enclave.rst b/docs/system/i386/nitro-enclave.rst
new file mode 100644
index 0000000000..3fb9e06893
--- /dev/null
+++ b/docs/system/i386/nitro-enclave.rst
@@ -0,0 +1,78 @@
+'nitro-enclave' virtual machine (``nitro-enclave``)
+===================================================
+
+``nitro-enclave`` is a machine type which emulates an ``AWS nitro enclave``
+virtual machine. `AWS nitro enclaves`_ is an `Amazon EC2`_ feature that allows
+creating isolated execution environments, called enclaves, from Amazon EC2
+instances which are used for processing highly sensitive data. Enclaves have
+no persistent storage and no external networking. The enclave VMs are based
+on Firecracker microvm with a vhost-vsock device for communication with the
+parent EC2 instance that spawned it and a Nitro Secure Module (NSM) device
+for cryptographic attestation. The parent instance VM always has CID 3 while
+the enclave VM gets a dynamic CID. Enclaves use an EIF (`Enclave Image Format`_)
+file which contains the necessary kernel, cmdline and ramdisk(s) to boot.
+
+In QEMU, ``nitro-enclave`` is a machine type based on ``microvm`` similar to how
+``AWS nitro enclaves`` are based on ``Firecracker`` microvm. This is useful for
+local testing of EIF files using QEMU instead of running real AWS Nitro Enclaves
+which can be difficult for debugging due to its roots in security. The vsock
+device emulation is done using vhost-user-vsock which means another process that
+can do the userspace emulation, like `vhost-device-vsock`_ from rust-vmm crate,
+must be run alongside nitro-enclave for the vsock communication to work.
+
+``libcbor`` and ``gnutls`` are required dependencies for nitro-enclave machine
+support to be added when building QEMU from source.
+
+.. _AWS nitro enlaves: https://docs.aws.amazon.com/enclaves/latest/user/nitro-enclave.html
+.. _Amazon EC2: https://aws.amazon.com/ec2/
+.. _Enclave Image Format: https://github.com/aws/aws-nitro-enclaves-image-format
+.. _vhost-device-vsock: https://github.com/rust-vmm/vhost-device/tree/main/vhost-device-vsock
+
+Using the nitro-enclave machine type
+------------------------------
+
+Machine-specific options
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+It supports the following machine-specific options:
+
+- nitro-enclave.vsock=string (required) (Id of the chardev from '-chardev' option that vhost-user-vsock device will use)
+- nitro-enclave.id=string (optional) (Set enclave identifier)
+- nitro-enclave.parent-role=string (optional) (Set parent instance IAM role ARN)
+- nitro-enclave.parent-id=string (optional) (Set parent instance identifier)
+
+
+Running a nitro-enclave VM
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+First, run `vhost-device-vsock`_ (or a similar tool that supports vhost-user-vsock).
+The forward-cid option below with value 1 forwards all connections from the enclave
+VM to the host machine and the forward-listen (port numbers separated by '+') is used
+for forwarding connections from the host machine to the enclave VM.
+
+  $ vhost-device-vsock \
+     --vm guest-cid=4,forward-cid=1,forward-listen=9001+9002,socket=/tmp/vhost4.socket
+
+Now run the necessary applications on the host machine so that the nitro-enclave VM
+applications' vsock communication works. For example, the nitro-enclave VM's init
+process connects to CID 3 and sends a single byte hello heartbeat (0xB7) to let the
+parent VM know that it booted expecting a heartbeat (0xB7) response. So you must run
+a AF_VSOCK server on the host machine that listens on port 9000 and sends the heartbeat
+after it receives the heartbeat for enclave VM to boot successfully. You should run all
+the applications on the host machine that would typically be running in the parent EC2
+VM for successful communication with the enclave VM.
+
+Then run the nitro-enclave VM using the following command where ``hello.eif`` is
+an EIF file you would use to spawn a real AWS nitro enclave virtual machine:
+
+  $ qemu-system-x86_64 -M nitro-enclave,vsock=c,id=hello-world \
+     -kernel hello-world.eif -nographic -m 4G --enable-kvm -cpu host \
+     -chardev socket,id=c,path=/tmp/vhost4.socket
+
+In this example, the nitro-enclave VM has CID 4. If there are applications that
+connect to the enclave VM, run them on the host machine after enclave VM starts.
+You need to modify the applications to connect to CID 1 (instead of the enclave
+VM's CID) and use the forward-listen (e.g., 9001+9002) option of vhost-device-vsock
+to forward the ports they connect to.
+
+.. _vhost-device-vsock: https://github.com/rust-vmm/vhost-device/tree/main/vhost-device-vsock#using-the-vsock-backend
-- 
2.39.5