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

[Elliot Berman <quic_eberman@quicinc.com>]

On 9/28/2022 8:43 PM, Bagas Sanjaya wrote:
> 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.
> 

Thanks! Applied for next version.