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 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.

Ian.


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