On 6/13/23 12:20 PM, Elliot Berman wrote:
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.
s/based/base/
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>
I have some questions and comments. But I trust that you
can answer them and update your patch in a reasonable way
to address what I say. So... please consider these things,
and update as you see fit.
Reviewed-by: Alex Elder <elder@xxxxxxxxxx>
---
Documentation/virt/gunyah/index.rst | 113 ++++++++++++++++++++
Documentation/virt/gunyah/message-queue.rst | 63 +++++++++++
Documentation/virt/index.rst | 1 +
3 files changed, 177 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 0000000000000..74aa345e0a144
--- /dev/null
+++ b/Documentation/virt/gunyah/index.rst
@@ -0,0 +1,113 @@
+.. 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.
s/VCPUS/VCPUs/
+ 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.
This might sound dumb, but can there be more vCPUs than there
are physical CPUs? Is a vCPU *tied* to a particular physical
CPU, or does it just indicate that a VM has one abstracted CPU
available to use--and any available physical CPU core can
implement it (possibly changing between time slices)?
+
+- 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 gh_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
Maybe:
This node lets Linux know it is running as a Gunyah guest VM.
It provides a basic description and capabilities of the VM,
as well as information required to communicate with the resource
manager.
+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 0000000000000..b352918ae54b4
--- /dev/null
+++ b/Documentation/virt/gunyah/message-queue.rst
@@ -0,0 +1,63 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Message Queues
+==============
+Message queue is a simple low-capacity IPC channel between two VMs. It is
I don't know what the "capacity" of an IPC channel is. But
that's OK I guess; it's sort of descriptive.
+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
+ with the message to inform the hypervisor to add the message to
+ message queue 1's queue. The hypervisor copies memory into the internal
+ message queue representation; the memory doesn't need to be shared between
+ VM_A and VM_B.
+
+2. Gunyah raises the corresponding interrupt for VM_B (Rx vIRQ) 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.
s/Explicility/Explicitly/
Is gh_msgq_send() a function and gh_msgq_push a "command" or
something? Why the difference in parentheses? (Pick a
convention and follow it.)
Does "Queue is flushed" mean "VM_B is interrupted"?
VM_A calls gh_msgq_push, and that causes the VM_B interrupt to
be signaled?
I'm being a little picky but I think these descriptions could be
improved a bit.
+ c. Message queue has reached a threshold depth.
+
+3. VM_B calls gh_msgq_recv() and Gunyah copies message to requested buffer.
It sure would be nice if all this didn't have to be copied
twice. But I recognize the copies ensure isolation.
+
+4. Gunyah buffers messages in the queue. If the queue became full when VM_A added a message,
+ the return values for gh_msgq_send() include a flag that indicates the queue is full.
+ Once VM_B receives the message and, thus, there is space in the queue, Gunyah
+ will raise the Tx vIRQ on VM_A to indicate it can continue sending messages.
Does the Tx vIRQ on VM_A fire after *every* message is sent,
or only when the state of the queue goes from "full" to "not"?
(Looking at patch 6 it looks like the latter.)
If it's signaled after every message is sent, does it
indicate that the message has been *received* by VM_B
(versus just received and copied by Gunyah)?
+
+For VM_B to send a message to VM_A, the process is identical, except that hypercalls
+reference message queue 2's capability ID. Each message queue has its own independent
+vIRQ: two TX message queues will have two vIRQs (and two capability IDs).
+
+::
+
+ +---------------+ +-----------------+ +---------------+
+ | 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 7fb55ae08598d..15869ee059b35 100644
--- a/Documentation/virt/index.rst
+++ b/Documentation/virt/index.rst
@@ -16,6 +16,7 @@ Virtualization Support
coco/sev-guest
coco/tdx-guest
hyperv/index
+ gunyah/index
.. only:: html and subproject
