Re: [Xen-devel] PCI Passthrough Design - Draft 3

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-08-11 at 16:34 -0400, Konrad Rzeszutek Wilk wrote:
> 
> > 2.2    PHYSDEVOP_pci_host_bridge_add hypercall
> > ----------------------------------------------
> > Xen code accesses PCI configuration space based on the sbdf received from
> > the
> > guest. The order in which the pci device tree node appear may not be the
> > same
> > order of device enumeration in dom0. Thus there needs to be a mechanism to
> > bind
> > the segment number assigned by dom0 to the pci host controller. The
> > hypercall
> > is introduced:
> 
> Why can't we extend the existing hypercall to have the segment value?
> 
> Oh wait, PHYSDEVOP_manage_pci_add_ext does it already!
> 
> And have the hypercall (and Xen) be able to deal with introduction of PCI
> devices that are out of sync?
> 
> Maybe I am confused but aren't PCI host controllers also 'uploaded' to
> Xen?

The issue is that Dom0 and Xen need to agree on a common numbering space
for the "PCI domain" AKA "segment", which is really just a software concept
i.e. on ARM Linux just makes them up (on x86 I believe they come from some
firmware table so Xen and Dom0 "agree" to both use that).

Ian.


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