Re: [Xen-devel] [PATCH v3 18/24] xen/passthrough: iommu_deassign_device_dt: By default reassign device to nobody

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-03-10 at 15:29 +0000, Julien Grall wrote:
> Hi,
> 
> On 23/02/15 15:34, Ian Campbell wrote:
> > On Mon, 2015-02-23 at 10:10 +0000, Julien Grall wrote:
> >>
> >> On 20/02/2015 17:04, Ian Campbell wrote:
> >>> On Tue, 2015-01-13 at 14:25 +0000, Julien Grall wrote:
> >>>> Currently, when the device is deassigned from a domain, we directly 
> >>>> reassign
> >>>> to DOM0.
> >>>>
> >>>> As the device may not have been correctly reset, this may lead to 
> >>>> corruption or
> >>>> expose some part of DOM0 memory. Also, we may have no way to reset some
> >>>> platform devices.
> >>>>
> >>>> If Xen reassigns the device to "nobody", it may receive some 
> >>>> global/context
> >>>> fault because the transaction has failed (indeed the context has been
> >>>> marked invalid). Unfortunately there is no simple way to quiesce a buggy
> >>>> hardware. I think we could live with that for a first version of platform
> >>>> device passthrough.
> >>>>
> >>>> DOM0 will have to issue an hypercall to assign the device to itself if it
> >>>> wants to use it.
> >>>
> >>> Does this behaviour differ from x86?
> > 
> > I realise now that x86 is a red-herring, what I really meant was differ
> > from other types of device (specifically PCI ones).
> > 
> >>  If so then it is worth calling that
> >>> out explicitly (even if not, good to know I think!)
> >>
> >> What do you mean by "calling that out explicitly"?
> > 
> > Stating in the commit log or a suitably placed comment (at least under
> > xen/include/public hopefully) that deassignment of dt devices behaves
> > differently to deassignment of other types of devices.
> 
> I tried to search any documentation explaining the behavior of those
> DOMCTL for PCI (mostly the deassign one) but I didn't find any.
> 
> By any chance, do you know if there is one? If so where?

If you didn't find it in the obvious places under xen/include/public
then it probably doesn't exist.

Ian.


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