Re: xsa46-4.2.patch breaks PCI passthrough?

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 01/05/13 16:26, Steven Haigh wrote:
> On 2/05/2013 1:18 AM, George Dunlap wrote:
>> On Wed, May 1, 2013 at 6:29 AM, Steven Haigh <netwiz@crc.id.au> wrote:
>>> Hi all,
>>>
>>> I've had a report lodged against my packages that the patch provided for
>>> XSA46 against Xen 4.2.1 causes PCI passthru to break.
>>>
>>> It seems that 4.2.1 *without* the XSA46 patch works perfectly. 4.2.2 does
>>> not work.
>> Have you tried this with xen-unstable tip?  That would be a blocker
>> bug for the 4.3 release.
> Hi George,
>
> It hasn't been tried it against anything other than 4.2.1 & 4.2.2 as 
> yet. As I'm not the end user with the problem here, I need to wait for 
> feedback.
>
> I have passed the patch provided by Andrew to the bug author - when I've 
> got feedback on this I'll be able to provide more information. I think 
> when we've got a root cause for this then it should be simple to verify 
> it on 4.3.
>

I have been investigating this issue on XenServer.

On XenServer, PCIPassthrough to a SLES11SP1 guest is working correctly,
even with the XSA-46 patch applied.

When passing through physical devices, my hypervisor debugging is being
triggered, but the actions of XEN_DOMCTL_irq_permission appear to be
correct, given sensible input from the Xapi toolstack.  When passing
through an SRIOV virtual function, no hypervisor debugging is being
triggered.

At a preliminary guess, I would say that XM looks to be doing something
stupid which it used to be getting away with, but is not now given the
changed in the hypervisor.

I suspect that it will be hard to progress this issue until Gordan
applied my debugging patch and gets back with the results.

~Andrew