Re: [Xen-devel] Re: [PATCH] AMD IOMMU: Hanlde sibling device assignment correctly

[David Edmondson <dme@xxxxxxx>]

On 7 May 2008, at 2:09pm, Keir Fraser wrote:
> On 7/5/08 11:17, "Wei Wang2" <wei.wang2@xxxxxxx> wrote:
>
> > > This patch seems to do more than you suggest, for example adding  
> > > an extra
> > > iommu hook into setup.c for dom0.
> > My idea is to let dom0 construct pci device list according to
> > configuration of pciback.hide=(). If a device is not hidden from  
> > dom0,
> > it might be in use by dom0, then it could be dangerous to assign  
> > any of
> > its siblings to other passthru domain. It is not very clean to hook  
> > into
> > setup.c but I failed to find any better way to this  :(
> I might be confused about how this works. Are you saying that if a  
> domU gets
> a device passed-thru that is a sibling of a dom0-driven device, then  
> dom0
> will mistakenly have its device's DMAs remapped according to the domU
> mappings that get set up?
If a device is behind a PCI-E to PCI bridge there are cases where  
transactions from the device are re-written by the bridge to use the  
requestor id of the bridge. Given that the requestor id is the token  
used by the IOMMU to determine the domain which initiated the IO, this  
effectively means that devices behind a PCI-E to PCI bridge are not  
divisible - they (and the bridge) must all be assigned to the same  
domain.
At least, that's my understanding :-/


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