On Tue, Apr 30, 2013 at 09:30:12AM +0200, Paolo Bonzini wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Il 30/04/2013 04:23, David Gibson ha scritto: > >>> I think this is a different problem. Basically the question is > >>> "what happens if a MemoryRegion 'disappears' while an > >>> AddressSpace is still referring to it", and the answer right > >>> now is "badness". > >> > >> Well.. no. The same problem may well exist for AddressSpace > >> objects, but in this case it's for the VFIO private > >> per-address-space object. > > Well, once we clarify the lifetime of AddressSpaces, we can clarify > the lifetime of the VFIO private object.
Hrm. I don't see why. The VFIO private data is tied to the
MemoryRegion, not an AddressSpace since that's what represents the
iommu.
> >>> We should look at generic fixes before dropping hooks in the
> >>> code. At the very least an "assert(mr->parent == NULL);" is
> >>> missing in memory_region_destroy.
> >>
> >> Well, sure that's probably also a good idea. But the whole point
> >> here is you're insisting that the MemoryRegion code doesn't know
> >> about the vfio private data, even as an opaque handle, and so
> >> there's no possible assert we can put there to check it has been
> >> destroyed.
> >
> > Oh, yes, forgot to ask. I'm still unclear on what the conceptual
> > difference is supposed to between a MemoryRegion and an
> > AddressSpace. AFAICT AddressSpace seems to be roughly just a
> > wrapper on a MemoryRegion that gives it some more features.
>
> Yes, an AddressSpace is a wrapper for a MemoryRegion that has a NULL
> - ->parent, with two extra features:
>
> - - QEMU computes the "flat" view of the MemoryRegion and a compressed
> radix tree representation of that view
Ok. It's not clear to me what that means in practice.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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