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