[PATCH v4 01/14] docs: gunyah: Introduce Gunyah Hypervisor

Elliot Berman
2022-09-28T19:57:31Z

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.

Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
---
Documentation/virt/gunyah/index.rst | 114 ++++++++++++++++++++
Documentation/virt/gunyah/message-queue.rst | 52 +++++++++
Documentation/virt/index.rst | 1 +
MAINTAINERS | 7 ++
4 files changed, 174 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
index 000000000000..959f451caccd
--- /dev/null
+++ b/Documentation/virt/gunyah/index.rst
@@ -0,0 +1,114 @@
+.. 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 and 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 devices 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 devices are referenced by a "capability IDs" and not a
+"resource IDs". A VM can have multiple capability IDs mapping to the same resource. If 2 VMs have
+access to the same resource, they may not be using the same capability ID to access that resource
+since the 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. On arm64, RM runs at 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, 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..e130f124ed52
--- /dev/null
+++ b/Documentation/virt/gunyah/message-queue.rst
@@ -0,0 +1,52 @@
+.. 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 object is unidirectional, so a full-duplex IPC channel requires a pair of
+objects.
+
+Messages can be up to 1024 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 1024 bytes in length. It raises a hypercall
+ with the message to inform the hypervisor to add the message to
+ message queue 1's queue.
+2. Gunyah raises the corresponding interrupt for VM_B when any of these happens:
+ a. gh_msgq_send has PUSH flag. Queue is immediately flushed. This is the typical case.
+ b. Explicility with gh_msgq_push command from VM_A.
+ c. Message queue has reached a threshold depth.
+3. VM_B calls gh_msgq_recv and Gunyah copies message to requested buffer.
+
+For VM_B to send a message to VM_A, the process is identical, except that hypercalls
+reference message queue 2's capability ID.
+
+::
+
+ +---------------+ +-----------------+ +---------------+
+ | VM_A | |Gunyah hypervisor| | VM_B |
+ | | | | | |
+ | | | | | |
+ | | Tx | | | |
+ | |-------->| | Rx vIRQ | |
+ |gh_msgq_send() | Tx vIRQ |Message queue 1 |-------->|gh_msgq_recv() |
+ | |<------- | | | |
+ | | | | | |
+ | Message Queue | | | | Message Queue |
+ | driver | | | | driver |
+ | | | | | |
+ | | | | | |
+ | | | | Tx | |
+ | | Rx vIRQ | |<--------| |
+ |gh_msgq_recv() |<--------|Message queue 2 | Tx vIRQ |gh_msgq_send() |
+ | | | |-------->| |
+ | | | | | |
+ | | | | | |
+ +---------------+ +-----------------+ +---------------+
diff --git a/Documentation/virt/index.rst b/Documentation/virt/index.rst
index 2f1cffa87b1b..418d540f5484 100644
--- a/Documentation/virt/index.rst
+++ b/Documentation/virt/index.rst
@@ -15,6 +15,7 @@ Linux Virtualization Support
acrn/index
coco/sev-guest
hyperv/index
+ gunyah/index

.. only:: html and subproject

diff --git a/MAINTAINERS b/MAINTAINERS
index f5ca4aefd184..e88ebb7cbcb8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8880,6 +8880,13 @@ L: linux-efi@vger.kernel.org
S: Maintained
F: block/partitions/efi.*

+GUNYAH HYPERVISOR DRIVER
+M: Elliot Berman <quic_eberman@quicinc.com>
+M: Murali Nalajala <quic_mnalajal@quicinc.com>
+L: linux-arm-msm@vger.kernel.org
+S: Supported
+F: Documentation/virt/gunyah/
+
HABANALABS PCI DRIVER
M: Oded Gabbay <ogabbay@kernel.org>
S: Supported
--
2.25.1