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

Bagas Sanjaya
2022-09-29T03:43:49Z

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On Wed, Sep 28, 2022 at 12:56:20PM -0700, Elliot Berman wrote:
> 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.

The documentation LGTM.

> 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
> <snipped>...
> +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.
> +

The nested list above should be separated with blank lines to be
rendered properly:

---- >8 ----

diff --git a/Documentation/virt/gunyah/message-queue.rst b/Documentation/virt/gunyah/message-queue.rst
index e130f124ed525a..afaad99db215e6 100644
--- a/Documentation/virt/gunyah/message-queue.rst
+++ b/Documentation/virt/gunyah/message-queue.rst
@@ -20,9 +20,11 @@ queue 2 allows VM_B to send messages to VM_A.
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

Thanks.

--
An old man doll... just what I always wanted! - Clara

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