Gunyah is an open-source Type-1 hypervisor developed by Qualcomm. It
does not depend on any lower-privileged OS/kernel code for its core
functionality. This increases its security and can support a smaller
trusted computing based when compared to Type-2 hypervisors.
Add documentation describing the Gunyah hypervisor and the main
components of the Gunyah hypervisor which are of interest to Linux
virtualization development.
Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx>
Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>
---
Documentation/virt/gunyah/index.rst | 113 ++++++++++++++++++++
Documentation/virt/gunyah/message-queue.rst | 61 +++++++++++
Documentation/virt/index.rst | 1 +
3 files changed, 175 insertions(+)
create mode 100644 Documentation/virt/gunyah/index.rst
create mode 100644 Documentation/virt/gunyah/message-queue.rst
diff --git a/Documentation/virt/gunyah/index.rst
b/Documentation/virt/gunyah/index.rst
new file mode 100644
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+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+Gunyah Hypervisor
+=================
+
+.. toctree::
+ :maxdepth: 1
+
+ message-queue
+
+Gunyah is a Type-1 hypervisor which is independent of any OS kernel,
and runs in
+a higher CPU privilege level. It does not depend on any
lower-privileged operating system
+for its core functionality. This increases its security and can
support a much smaller
+trusted computing base than a Type-2 hypervisor.
+
+Gunyah is an open source hypervisor. The source repo is available at
+https://github.com/quic/gunyah-hypervisor.
+
+Gunyah provides these following features.
+
+- Scheduling:
+
+ A scheduler for virtual CPUs (vCPUs) on physical CPUs enables
time-sharing
+ of the CPUs. Gunyah supports two models of scheduling:
+
+ 1. "Behind the back" scheduling in which Gunyah hypervisor
schedules vCPUS on its own.
+ 2. "Proxy" scheduling in which a delegated VM can donate part of
one of its vCPU slice
+ to another VM's vCPU via a hypercall.
+
+- Memory Management:
+
+ APIs handling memory, abstracted as objects, limiting direct use of
physical
+ addresses. Memory ownership and usage tracking of all memory under
its control.
+ Memory partitioning between VMs is a fundamental security feature.
+
+- Interrupt Virtualization:
+
+ Uses CPU hardware interrupt virtualization capabilities. Interrupts
are handled
+ in the hypervisor and routed to the assigned VM.
+
+- Inter-VM Communication:
+
+ There are several different mechanisms provided for communicating
between VMs.
+
+- Virtual platform:
+
+ Architectural devices such as interrupt controllers and CPU timers
are directly provided
+ by the hypervisor as well as core virtual platform devices and
system APIs such as ARM PSCI.
+
+- Device Virtualization:
+
+ Para-virtualization of devices is supported using inter-VM
communication.
+
+Architectures supported
+=======================
+AArch64 with a GIC
+
+Resources and Capabilities
+==========================
+
+Some services or resources provided by the Gunyah hypervisor are
described to a virtual machine by
+capability IDs. For instance, inter-VM communication is performed
with doorbells and message queues.
+Gunyah allows access to manipulate that doorbell via the capability
ID. These resources are
+described in Linux as a struct gunyah_resource.
+
+High level management of these resources is performed by the resource
manager VM. RM informs a
+guest VM about resources it can access through either the device tree
or via guest-initiated RPC.
+
+For each virtual machine, Gunyah maintains a table of resources which
can be accessed by that VM.
+An entry in this table is called a "capability" and VMs can only
access resources via this
+capability table. Hence, virtual Gunyah resources are referenced by a
"capability IDs" and not
+"resource IDs". If 2 VMs have access to the same resource, they might
not be using the same
+capability ID to access that resource since the capability tables are
independent per VM.
+
+Resource Manager
+================
+
+The resource manager (RM) is a privileged application VM supporting
the Gunyah Hypervisor.
+It provides policy enforcement aspects of the virtualization system.
The resource manager can
+be treated as an extension of the Hypervisor but is separated to its
own partition to ensure
+that the hypervisor layer itself remains small and secure and to
maintain a separation of policy
+and mechanism in the platform. RM runs at arm64 NS-EL1 similar to
other virtual machines.
+
+Communication with the resource manager from each guest VM happens
with message-queue.rst. Details
+about the specific messages can be found in
drivers/virt/gunyah/rsc_mgr.c
+
+::
+
+ +-------+ +--------+ +--------+
+ | RM | | VM_A | | VM_B |
+ +-.-.-.-+ +---.----+ +---.----+
+ | | | |
+ +-.-.-----------.------------.----+
+ | | \==========/ | |
+ | \========================/ |
+ | Gunyah |
+ +---------------------------------+
+
+The source for the resource manager is available at
https://github.com/quic/gunyah-resource-manager.
+
+The resource manager provides the following features:
+
+- VM lifecycle management: allocating a VM, starting VMs, destruction
of VMs
+- VM access control policy, including memory sharing and lending
+- Interrupt routing configuration
+- Forwarding of system-level events (e.g. VM shutdown) to owner VM
+
+When booting a virtual machine which uses a devicetree such as Linux,
resource manager overlays a
+/hypervisor node. This node can let Linux know it is running as a
Gunyah guest VM,
+how to communicate with resource manager, and basic description and
capabilities of
+this VM. See
Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml for
a description
+of this node.
diff --git a/Documentation/virt/gunyah/message-queue.rst
b/Documentation/virt/gunyah/message-queue.rst
new file mode 100644
index 000000000000..0667b3eb1ff9
--- /dev/null
+++ b/Documentation/virt/gunyah/message-queue.rst
@@ -0,0 +1,61 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Message Queues
+==============
+Message queue is a simple low-capacity IPC channel between two VMs.
It is
+intended for sending small control and configuration messages. Each
message
+queue is unidirectional, so a full-duplex IPC channel requires a pair
of queues.
+
+Messages can be up to 240 bytes in length. Longer messages require a
further
+protocol on top of the message queue messages themselves. For
instance, communication
+with the resource manager adds a header field for sending longer
messages via multiple
+message fragments.
+
+The diagram below shows how message queue works. A typical
configuration involves
+2 message queues. Message queue 1 allows VM_A to send messages to
VM_B. Message
+queue 2 allows VM_B to send messages to VM_A.
+
+1. VM_A sends a message of up to 240 bytes in length. It raises a
hypercall
