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

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
towards the end of the session. I've tried to attribute names against
comments but have very likely got things mixed up. Apologies in
Was curious if any discussions happened on the RC Emu (config space
emulation) as per slide 18

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:


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

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.


Julien Grall

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