Re: [Xen-devel] Notes from PCI Passthrough design discussion at Xen Summit

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 20/07/17 12:00, Manish Jaggi wrote:
> On 7/20/2017 4:11 PM, Julien Grall wrote:
> > On 20/07/17 10:32, Manish Jaggi wrote:
> > > Hi Roger,
> > >
> > > On 7/20/2017 1:54 PM, Roger Pau Monné wrote:
> > > > On Thu, Jul 20, 2017 at 09:24:36AM +0530, Manish Jaggi wrote:
> > > > > Hi Punit,
> > > > >
> > > > > On 7/19/2017 8:11 PM, Punit Agrawal wrote:
> > > > > > I took some notes for the PCI Passthrough design discussion at Xen
> > > > > > Summit. Due to the wide range of topics covered, the notes got
> > > > > > sparser
> > > > > > towards the end of the session. I've tried to attribute names against
> > > > > > comments but have very likely got things mixed up. Apologies in
> > > > > > advance.
> > > > > Was curious if any discussions happened on the RC Emu (config space
> > > > > emulation) as per slide 18
> > > > > https://schd.ws/hosted_files/xendeveloperanddesignsummit2017/76/slides.pdf
> > > > Part of this is already posted on the list (ATM for x86 only) but the
> > > > PCI specification (and therefore the config space emulation) is not
> > > > tied to any arch:
> > > >
> > > > https://lists.xenproject.org/archives/html/xen-devel/2017-06/msg03698.html
> > > From the summary, I have a  questions on
> > > "
> > >  - Roger: Registering config space with Xen before device discovery
> > >   will allow the hypervisor to set access traps for certain
> > >  functionality as appropriate"
> > >
> > > Traps will do emulation or something else ?
> > >  Is the config space emulation only for DomU or it for Dom0 as well ?
> > > Slide 18 shows only for DomU ?
> > My slides are not meant to be read without the talk. In this
> > particular case, this is only explaining how passthrough will work for
> > DomU.
> Thanks for clarification.
> Ah ok, The single slide created confusion, It would be nice if you have
> added one more describing dom0 config access. I will wait for the video
> to get posted.
Well as I said my slides are not meant to be used without the talk.

Now, if you want the longer story. The decision for DOM0 is more blur. 
As written in the design document and also reported in the notes from 
Punit, supported all the hostbridges in Xen may not be possible.
At the moment, we are thinking to only support fully ECAM compliant in 
Xen (i.e the ones not requiring specific PCI hostbridges driver). We 
might bend the rule on the case by case basis in the future.
For the hostbridges not supported in Xen, they will be driven by the 
hardware domain. So all configuration access will be forwarded to the 
hardware domain. The way to communicate between Xen and the hardware 
Domain is still undecided and out of scope of this design document.
Cheers,

--
Julien Grall

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