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Re: [Qemu-ppc] [Qemu-devel] [PATCH 11/11] vfio: Add guest side IOMMU sup

From: David Gibson
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH 11/11] vfio: Add guest side IOMMU support
Date: Thu, 16 May 2013 16:53:47 +1000
User-agent: Mutt/1.5.21 (2010-09-15)

On Wed, May 15, 2013 at 01:32:50PM +1000, David Gibson wrote:
> On Tue, May 14, 2013 at 08:51:08PM -0600, Alex Williamson wrote:
> > On Wed, 2013-05-15 at 11:33 +1000, David Gibson wrote:
> > > On Tue, May 14, 2013 at 11:15:26AM -0600, Alex Williamson wrote:
> > > > On Tue, 2013-05-14 at 19:13 +1000, David Gibson wrote:
> > Trying to make sure I understand why guest_iommus is a list.  We can
> > have multiple guest iommus, but in the majority of those cases I would
> > expect only one iommu per VFIOAddressSpace.  So if the listener is for
> > this space, we only add the relevant iommu and not all of the iommus in
> > the machine.
> That's what we do - we only add notifiers for iommu regions that
> appear within the relevant address space.  It's a list because at
> least theoretically there could be more than one iommu region in the
> AS, although I don't know of any real cases where that would be true.
> >  Actually maybe two guest iommu ranges are common for spapr
> > per space, a 32bit and a 64bit range?
> I think 64-bit DMA windows on PAPR are usually just mapped to RAM with
> a fixed offset, rather than having TCEs (page table).  That might well
> introduce some extra complexities in how we mirror that into VFIO, but
> it's not directly relevant to this point.

So, since I wrote that I've heard from Ben that while current machines
don't have multiple (translated) iommu windows, this could well be
found on future machines.

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_!

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