Re: [Qemu-devel] Re: Status update

[Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>]

On Fri, Jul 02, 2010 at 06:41:55PM +0900, Isaku Yamahata wrote:
> On Fri, Jul 02, 2010 at 09:03:39AM +0100, Stefan Hajnoczi wrote:
> > On Thu, Jul 1, 2010 at 8:30 PM, Eduard - Gabriel Munteanu
> > <eduard.munteanu@linux360.ro> wrote:
> > > But suddenly the guest OS changes mappings and expects the IOMMU to
> > > enforce them as soon as invalidation commands are completed. The guest
> > > then reclaims the old space for other uses. This leaves an opportunity
> > > for those processes to corrupt or read sensitive data.
> 
> In such a case, OS should put device into quiescence by reset like
> pci bus reset or pcie function level reset.
> pci bus reset patch hasn't been merged yet, though.
> It needs clean up/generalization.
> 
> -- 
> yamahata

I wouldn't count on that. When the IOMMU notifies software of command
completion, then that notification should be correct. So if we count on
'pci bus reset' we either don't execute INVALIDATE_* and COMPLETION_WAIT
commands, or we issue bogus notifications (e.g. they'd be nops). That
goes against the specs, and I'm not sure there's any good reason a
non-KVM/QEMU-aware OS would reset the device in _all_ cases.

For some background on this, mappings updates are followed by
INVALIDATE_* commands and then a COMPLETION_WAIT (to wait for
invalidation to finish).


	Eduard