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 08:14, Gordan Bobic <gordan@xxxxxxxxxx> wrote:
> On 03/20/2014 12:48 AM, Zhang, Yang Z 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.
> 
> I'm not sure if I'm reading this right, but you wouldn't necessarily be 
> passing all devices under a particular bridge to guests (and certainly 
> not necessarily to the same guest). You could have multiple levels of 
> bridges to provide extra PCIe links. One obvious example is dual GPU 
> cards where both GPUs are under a bridge, but you wouldn't necessarily 
> be passing both devices to a guest (one might be the primary GPU for the 
> host).

PCIe devices behind PCI bridges still need to be treated as PCI ones
(i.e. not necessarily presenting their own IDs in transactions, due to
the intermediate non-express bridge). And it's only the non-PCIe
case we're talking about here - no problems of this kind are known for
PCIe devices.

Jan


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