Re: [Xen-devel] [PATCH] Add device_model_pvdevice parameter for HVM guests

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Ian Jackson [mailto:Ian.Jackson@xxxxxxxxxxxxx]
> Sent: 18 July 2013 12:01
> To: Paul Durrant
> Cc: xen-devel@xxxxxxxxxxxxx; Stefano Stabellini; Ian Campbell
> Subject: RE: [PATCH] Add device_model_pvdevice parameter for HVM
> guests
> 
> Paul Durrant writes ("RE: [PATCH] Add device_model_pvdevice parameter
> for HVM guests"):
> > > -----Original Message-----
> > > From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
> > > Sent: 04 July 2013 11:50
> > > To: xen-devel@xxxxxxxxxxxxx
> > > Cc: Paul Durrant; Stefano Stabellini
> > > Subject: [PATCH] Add device_model_pvdevice parameter for HVM
> guests
> > >
> > > The parameter determines which, if any, xen-pvdevice is specified on the
> > > QEMU command line. The default value is 'none' which means no
> argument
> > > will
> > > be passed. A value of 'xenserver' specifies a xen-pvdevice with device-id
> > > 0xc000 (the initial value in the xenserver namespace - see
> > > docs/misc/pci-device-reservations.txt).
> > >
> > > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > > Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> > > ---
> >
> > Re-ping? Stefano tells me he's waiting for an ack from either IanC or IanJ 
> > on
> this one before dealing with the QEMU end of things. It's aleady been acked
> by Matt Wilson.
> 
> Thanks for CCing this to me.  I don't seem to have any earlier
> versions in my mailbox.
> 
> When you say the "xen-pvdevice", you mean what has traditionally been
> called the "Xen platform PCI device" ?  Ie, the special PCI device
> that HVM guests are provided with to enable them to make hypercalls
> etc.
> 

No, this is a new device. See 
https://lists.gnu.org/archive/html/qemu-devel/2013-07/msg00733.html

> I see that 0xc000 has been reserved for use by Citrix XenServer.  But
> that's simply a reservation.  If we're actually going to use this
> value in our tree, we need some proper documentation of it.
> 
> I'm obviously missing some of the background.
> 

Yep. You should probably read the above thread. In summary though, the 
xen-pvdevice is a PCI device with configurable vendor, device and revision 
values, dedicated for use as a binding point for PV drivers in a guest. This 
patch adds code to libxl to create the 'XenServer' flavour of this device by 
name rather than number, for user-friendliness. 
I have added some explanation into xl.cfg.pod.5 but not explicitly called out 
the mapping of name to (vendor,device,revision) there - is that the kind of 
thing you'd like to see added?

  Paul

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