Re: [Qemu-devel] [PATCH V14 2/7] Add TPM (frontend) hardware interface (TPM TIS) to Qemu

[Stefan Berger]

On 02/21/2012 07:18 AM, Michael S. Tsirkin wrote:
> On Tue, Feb 21, 2012 at 06:19:26AM -0500, Stefan Berger wrote:
> > On 02/20/2012 10:18 PM, Michael S. Tsirkin wrote:
> > > On Mon, Feb 20, 2012 at 07:43:05PM -0500, Stefan Berger wrote:
> > > > On 02/20/2012 05:02 PM, Michael S. Tsirkin wrote:
> > > > > On Wed, Dec 14, 2011 at 08:43:17AM -0500, Stefan Berger wrote:
> > > Alternatively, I imagined that you can pass a copy
> > > or pointer of the necessary state to the backend,
> > > which queues the command and wakes the worker.
> > > In the reverse direction, backend queues a response
> > > and when OS polls you dequeue it and update state.
> > The OS doesn't necessarily need to poll. It is just one mode of
> > operation of the OS, the other being interrupt-driven where the
> > backend raises the interrupt once it has delivered the response to
> > the frontend.
> >
> >
> >     Stefan
> So you will also need to signal the frontend when it
> must interrupt the guest. This is not a problem,
> for example you can use a qemu_eventfd object for this.

When the backend delivers the response it checks whether the interface 
is used in interrupt mode and raises the interrupt. The backend enters 
the frontend code with a callback. In this function also a signal is 
sent that may wake up the main thread that, upon suspend, may be waiting 
for the last command to be processed and be sleeping on a condition 
variable.

I now added a function to the backend interface that is invoked by the 
frontend to notify the backend of a TPM request. The backend code can 
then either notify a thread (passthrough and libtpms driver) or create a 
response right away and invoke that callback to the front-end to deliver 
the response (null driver). How frontend and backend handle 
notifications is isolated to the frontend and backend with some backends 
(libtpms, passthough) sharing the code for how the notification is done.

Stefan