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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Mar 20, 2014 at 10:02:01AM +0000, Jan Beulich wrote:
> >>> On 20.03.14 at 02:34, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> > On Mar 19, 2014 8:48 PM, "Zhang, Yang Z" <yang.z.zhang@intel.com> 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.

Aha! Thank you explaining. That would certainly make it easier.
> 
> > 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.

Right.
> 
> Jan
>