Re: VT-d support for device assignment

[Muli Ben-Yehuda <muli@il.ibm.com>]

On Fri, Aug 22, 2008 at 09:12:32PM +0300, Avi Kivity wrote:
> Muli Ben-Yehuda wrote:
> > With PCI passthrough It is possible in theory to log mmio's and pio's
> > executed by the guest, as well as interrupts delivered to the guest,
> > although it will have a performance impact. It is not possible to log
> > DMAs in a simple manner, but you could hook up a PCI analyzer to get
> > the missing bits.
> >   
> 
> Well, with a pci analyzer you can log anything going in and out of
> the device; you don't need a virtual machine monitor.

Yep, that's true. I was thinking along the lines of doing the bulk of
reverse engineering without a PCI analyzer (if you understand the
device well enough, looking at the DMA data may not be all that
important) and then using a PCI analyzer just for any remaining bits.

By the way, with effort we should be able to capture some DMAs too,
either by taking "before" and "after" snapshots of VM memory (for DMA
write to memory) and/or by triggering DMA faults (by not mapping the
VM's memory in an isolation-capable IOMMU and enabling the IOMMU).

Cheers,
Muli
-- 
Workshop on I/O Virtualization (WIOV '08)
Co-located with OSDI '08, Dec 2008, San Diego, CA
http://www.usenix.org/wiov08