Re: [Xen-devel] Multiple platform PCI device ID registries?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-11-13 at 11:58 +0000, Paul Durrant wrote:

> > I'm concerned because that comment refers to XenServer 6.1 but it now
> > appears to be being reused as the default device ID for the "Xen
> > pvdevice".
> > 
> > Maybe it is safe to reuse this in this way, but the docs should be
> > updated I think.
> > 
> 
> I believe it is safe.

How would you describe it in that document? "Xen PV device (extended
platform device). Previously used in XenServer 6.1" ?

Is there some spec we can link to regarding how this device should be
used?

> > >  In practice it should never be used as the device ID should always be
> > > specified by the toolstack.
> > 
> > But it defaults to the Citrix ID -- is that wise? Wouldn't it be better
> > to default to nothing?
> > 
> 
> I guess we could default the prop to something like 0xffff and then
> fail the init fn if we find the value unmodified. Would that be
> better?

I think so, yes.

> > It also seems to be causing a moderate amount of fallout in the
> > "[Xen-devel] [BUG] Xen vm kernel crash in get_free_entries." thread.
> > 
> 
> As I understood it, that problem is slightly distinct. It's a case of
> someone bringing up HVM linux in a XenServer VM and then getting a
> crash because PVonHVM doesn't set up properly due to the change in
> device_id for the *platform* device.

How and when did this change? Was it just a XenServer quirk in a
particular version?

>  Using device ID to for the PV device should not cause such fallout as
> the platform device is left unmolested.
> 
> > I'm busy wondering if maybe Qemu should blacklist non-xenserver product
> > ids when it has been configured with the Xen PV device using the Citrix
> > devid?
> > 
> 
> That should not be necessary as the point of registering the devid is
> that on-one else creates driver that bind to that devid. Certainly
> no-one has to date.

The problem is that unplug time we don't necessarily have PCI yet to
know if we are going to be able to bind to the device which eventually
shows up.

Remind me: When the PV device is in use the platform device must always
be present? Right? That's the sort of thing which should be mentioned in
the spec I asked about above.

Ian.


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