Re: [Xen-devel] Dealing with non-existent BDF devices in VT-d and in the hardware.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.03.14 at 02:34, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> On Mar 19, 2014 8:48 PM, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
>> fake a device is a solution. But I am thinking (maybe I am wrong) why not 
> setup all VT-d entries under a bridge if passing a PCI device under a bridge. 
> Because when passing a PCI device under a bridge, all devices under bridge 
> should be assigned to the guest too. What current Xen dose is only set the 
> entry which has device, so why not extend it to setup all entries? In this 
> case, there is no user input is required.
> 
> We are talking about two different things here.

Not really.

> To your idea of passing in all of the devices along that are under a bridge 
> (or at least check for that) is sensible. We can't just pass in it in without 
> checking that the devices have been deassigned from the dom0 device drivers. 

That's what xend is doing, but xl isn't.

> But if they are all 'floating' and not being in use - sure (thought maybe 
> provide an option in the tool stack- we needn't to pass all of them if nobody 
> else is using them).

Aiui he wasn't suggesting to pass them all to the guest, just to put all
IDs in the IOMMU tables, such that no faults would arise if an ID other
then the root-most PCI bridge's one or that of any _existing_ device.

> The original issue in this thread was - what if any option should we come up 
> to work around broken firmware that uses non-existent BDFs. Should it be some 
> boot up parameter or should we alter an hyper call to allow creation of 
> phantom devices under a bridge. Then later it can be assigned as part of a 
> group to a guest.

With Yang's proposal - provided its security can be proven - you
wouldn't need any command line override.

Jan


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