Re: [Xen-devel] [TESTDAY] PV / HVM pass-through works when IOMMU present; weird failures when not

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 28/06/13 17:00, Jan Beulich wrote:
> > > > On 28.06.13 at 17:37, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> > - For HVM guests, the only user-visible indication tha the IOMMU has
> > been disabled is the following error message on the command-line:
> >
> > # xl pci-attach h0 07:00.0
> > libxl: error: libxl_pci.c:949:do_pci_add: xc_assign_device failed
> >
> > However, the device itself ends up passed-through to the guest anyway;
> > the guest seems to be able to see it and interact with it normally.
> > This is particularly scary, as in theory this should not be possible
> > without a working IOMMU.
> >
> > I don't think this is a blocker for 4.3, but we should definitely
> > release note it, and for 4.4 add a check to see if there is a
> > functioning IOMMU and only add a device if there's an override set.
> To me this very much looks like a security problem (which I
> think we should fix asap).
Is it worth delaying the release (yet) another week for?

Probably the simplest solution at the moment, if there's an easy way for 
the toolstack to figure out whether there is a working IOMMU or not, is 
to simply not allow pass-through without an IOMMU unless there is an 
override option.
Thoughts?
 -George

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