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

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

On Wed, Mar 19, 2014 at 12:32:31AM +0000, Zhang, Yang Z wrote:
> Konrad Rzeszutek Wilk wrote on 2014-03-18:
> > 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.
> >
> 
> Yes, this is missing.
> 
> > 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.
> 
> The question is that device 08:00.0 doesn't exist in your platform, you only saw the BDF in the DMA transaction. How can you add a non-exist device to a group? 

Why do I need to add it to a group? The patch I posted (see first email in this thread)
just made a fake PCI device in the Xen hypervisor. But I don't see libxl nor
QEMU doing any group operations - so why are they required? If I just bundle
all of the PCI devices underneath that bridge to the guest it should be OK, shouldn't it?

> 
> >> 
> >> Best regards,
> >> Yang
> >> 
> >>
> 
> 
> Best regards,
> Yang
>