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

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

On Mon, Mar 17, 2014 at 01:03:00AM +0000, Zhang, Yang Z wrote:
> Konrad Rzeszutek Wilk wrote on 2014-03-15:
> >> 
> >> What happens if you assign the devices under bus 09 to another guest?
> > 
> > Hadn't tried that. I think it would all blow up as the the
> > non-existent bridge is now assigned to one guest and the phantom DMA
> > requests for the
> > 09 would show up under the 08 device. I think I would corrupt the
> > guest memory with random DMA writes.
> > 
> >> Is it better to add Xen command line to add such devices to a group
> >> and
> > assign the whole group to a guest when trying to assign a device of
> > the group to guest?
> > 
> > Or implement the group assigment in QEMU or libxl so that nobody tries
> > doing it.
> 
> But I think user still need to tell which device is buggy manually and I don't think QEMU or libxl can do it.

I think there are two issues here: 

a) Missing device assigments via groups. That should be done irregardless
   if the device / hardware is buggy.

b) Buggy devices like the IDT bridge that I see. That is a seperate issue - and
   we just discussion if we want to inject that in the VT-d (or AMD-VI) what
   would be the mechanism to do that.

> 
> Best regards,
> Yang
> 
>