Re: [PATCH v14 16/25] docs: gunyah: Document Gunyah VM Manager

[Alex Elder]

On 6/13/23 12:20 PM, Elliot Berman wrote:
> Document the ioctls and usage of Gunyah VM Manager driver.
>
> Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>

A few minor comments below, but regardless:

Reviewed-by: Alex Elder <elder@xxxxxxxxxx>

> ---
>   Documentation/virt/gunyah/index.rst      |  1 +
>   Documentation/virt/gunyah/vm-manager.rst | 83 ++++++++++++++++++++++++
>   2 files changed, 84 insertions(+)
>   create mode 100644 Documentation/virt/gunyah/vm-manager.rst
>
> diff --git a/Documentation/virt/gunyah/index.rst b/Documentation/virt/gunyah/index.rst
> index 74aa345e0a144..7058249825b16 100644
> --- a/Documentation/virt/gunyah/index.rst
> +++ b/Documentation/virt/gunyah/index.rst
> @@ -7,6 +7,7 @@ Gunyah Hypervisor
>   .. toctree::
>      :maxdepth: 1
>   
> +   vm-manager
>      message-queue
>   
>   Gunyah is a Type-1 hypervisor which is independent of any OS kernel, and runs in
> diff --git a/Documentation/virt/gunyah/vm-manager.rst b/Documentation/virt/gunyah/vm-manager.rst
> new file mode 100644
> index 0000000000000..df0e1a8279bf5
> --- /dev/null
> +++ b/Documentation/virt/gunyah/vm-manager.rst
> @@ -0,0 +1,83 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=======================
> +Virtual Machine Manager
> +=======================
> +
> +The Gunyah Virtual Machine Manager is a Linux driver to support launching
> +virtual machines using Gunyah. It presently supports launching virtual machines
> +scheduled by Gunyah's scheduler.

You referred to this as "behind-the-back" scheduling in patch 1.
(I don't know if this terminology is important to use.)

> +
> +Configuration of a Gunyah virtual machine is done via a devicetree. When the VM
> +is launched, memory is provided by the host VM which contains the devictree.
> +Gunyah reads the devicetree to configure the memory map and create resources
> +such as vCPUs for the VM. Memory can be shared with the VM with
> +`GH_VM_SET_USER_MEM_REGION`_. Userspace can interact with the resources in Linux
> +by adding "functions" to the VM.
> +
> +Sample Userspace VMM
> +====================
> +
> +A sample userspace VMM is included in samples/gunyah/ along with a minimal
> +devicetree that can be used to launch a VM. To build this sample, enable
> +CONFIG_SAMPLE_GUNYAH.
> +
> +IOCTLs and userspace VMM flows
> +==============================
> +
> +The kernel exposes a char device interface at /dev/gunyah.
> +
> +To create a VM, use the `GH_CREATE_VM`_ ioctl. A successful call will return a
> +"Gunyah VM" file descriptor.

Maybe reword this a bit so it's clearer that the IOCTL calls
are performed on the file descriptor resulting from opening
/dev/gunyah?

> +
> +/dev/gunyah API Descriptions
> +----------------------------
> +
> +GH_CREATE_VM
> +~~~~~~~~~~~~
> +
> +Creates a Gunyah VM. The argument is reserved for future use and must be 0.
> +A successful call will return a Gunyah VM file descriptor. See
> +`Gunyah VM API Descriptions`_ for list of IOCTLs that can be made on this file

Maybe "the next section" rather than an explicit reference.
But it's fine as-is.

Also (because you duplicate "file"):

s/on this file/on this/

> +file descriptor.
> +
> +Gunyah VM API Descriptions
> +--------------------------
> +
> +GH_VM_SET_USER_MEM_REGION
> +~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +This ioctl allows the user to create or delete a memory parcel for a guest

How are memory parcels deleted?  (Maybe add a sentence at the end
of this section.)

> +virtual machine. Each memory region is uniquely identified by a label;
> +attempting to create two regions with the same label is not allowed. Labels are
> +unique per virtual machine.
> +
> +While VMM is guest-agnostic and allows runtime addition of memory regions,
> +Linux guest virtual machines do not support accepting memory regions at runtime.
> +Thus, for Linux guests, memory regions should be provided before starting the VM
> +and the VM must be configured via the devicetree to accept these at boot-up.
> +
> +The guest physical address is used by Linux kernel to check that the requested
> +user regions do not overlap and to help find the corresponding memory region
> +for calls like `GH_VM_SET_DTB_CONFIG`_. It must be page aligned.
> +
> +To add a memory region, call `GH_VM_SET_USER_MEM_REGION`_ with fields set as
> +described above.
> +
> +.. kernel-doc:: include/uapi/linux/gunyah.h
> +   :identifiers: gh_userspace_memory_region gh_mem_flags
> +
> +GH_VM_SET_DTB_CONFIG
> +~~~~~~~~~~~~~~~~~~~~
> +
> +This ioctl sets the location of the VM's devicetree blob and is used by Gunyah
> +Resource Manager to allocate resources. The guest physical memory must be part
> +of the primary memory parcel provided to the VM prior to GH_VM_START.
> +
> +.. kernel-doc:: include/uapi/linux/gunyah.h
> +   :identifiers: gh_vm_dtb_config
> +
> +GH_VM_START
> +~~~~~~~~~~~
> +
> +This ioctl starts the VM.