Re: [PATCH v9 01/18] docs: acrn: Introduce ACRN

[Shuo A Liu]

Hi Randy,

On Mon  8.Feb'21 at 11:48:07 -0800, Randy Dunlap wrote:
> On 2/6/21 7:10 PM, shuo.a.liu@xxxxxxxxx wrote:
> > From: Shuo Liu <shuo.a.liu@xxxxxxxxx>
> >
> > Add documentation on the following aspects of ACRN:
> >
> >   1) A brief introduction on the architecture of ACRN.
> >   2) I/O request handling in ACRN.
> >   3) CPUID functions of ACRN.
>
> > ---
>
> > diff --git a/Documentation/virt/acrn/io-request.rst b/Documentation/virt/acrn/io-request.rst
> > new file mode 100644
> > index 000000000000..6cc3ea0fa1f5
> > --- /dev/null
> > +++ b/Documentation/virt/acrn/io-request.rst
> > @@ -0,0 +1,97 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +I/O request handling
> > +====================
> > +
> ...
> > +
> > +1. 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.
>
> Does this mean that ACRN has a limit of 16 vCPUs ?

Yes. Now it is a limitation.

Thanks
shuo