Re: [PATCH v8 09/18] virt: acrn: Introduce I/O request management

[Davidlohr Bueso]

On Fri, 22 Jan 2021, shuo.a.liu@xxxxxxxxx wrote:

> From: Shuo Liu <shuo.a.liu@xxxxxxxxx>
>
> An I/O request of a User VM, which is constructed by the hypervisor, is
> distributed by the ACRN Hypervisor Service Module to an I/O client
> corresponding to the address range of the I/O request.
>
> For each User VM, there is a shared 4-KByte memory region used for I/O
> requests communication between the hypervisor and Service VM. An I/O
> request is a 256-byte structure buffer, which is 'struct
> acrn_io_request', that is filled by an I/O handler of the hypervisor
> when a trapped I/O access happens in a User VM. ACRN userspace in the
> Service VM first allocates a 4-KByte page and passes the GPA (Guest
> Physical Address) of the buffer to the hypervisor. The buffer is used as
> an array of 16 I/O request slots with each I/O request slot being 256
> bytes. This array is indexed by vCPU ID.
>
> An I/O client, which is 'struct acrn_ioreq_client', is responsible for
> handling User VM I/O requests whose accessed GPA falls in a certain
> range. Multiple I/O clients can be associated with each User VM. There
> is a special client associated with each User VM, called the default
> client, that handles all I/O requests that do not fit into the range of
> any other I/O clients. The ACRN userspace acts as the default client for
> each User VM.
>
> The state transitions of a ACRN I/O request are as follows.
>
>   FREE -> PENDING -> PROCESSING -> COMPLETE -> FREE -> ...
>
> FREE: this I/O request slot is empty
> PENDING: a valid I/O request is pending in this slot
> PROCESSING: the I/O request is being processed
> COMPLETE: the I/O request has been processed
>
> An I/O request in COMPLETE or FREE state is owned by the hypervisor. HSM
> and ACRN userspace are in charge of processing the others.
>
> The processing flow of I/O requests are listed as following:
>
> a) The I/O handler of the hypervisor will fill an I/O request with
>   PENDING state when a trapped I/O access happens in a User VM.
> b) The hypervisor makes an upcall, which is a notification interrupt, to
>   the Service VM.
> c) The upcall handler schedules a worker to dispatch I/O requests.
> d) The worker looks for the PENDING I/O requests, assigns them to
>   different registered clients based on the address of the I/O accesses,
>   updates their state to PROCESSING, and notifies the corresponding
>   client to handle.
> e) The notified client handles the assigned I/O requests.
> f) The HSM updates I/O requests states to COMPLETE and notifies the
>   hypervisor of the completion via hypercalls.
>
> Signed-off-by: Shuo Liu <shuo.a.liu@xxxxxxxxx>
> Reviewed-by: Zhi Wang <zhi.a.wang@xxxxxxxxx>
> Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Cc: Zhi Wang <zhi.a.wang@xxxxxxxxx>
> Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
> Cc: Yu Wang <yu1.wang@xxxxxxxxx>
> Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>

Thanks for respinning this with a workqueue.

Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>