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Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Alex Williamson <alex.williamson@redhat.com>
Date: Wed, 19 Jun 2013 14:59:30 +1000
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Cc: kvm@vger.kernel.org, Alexey Kardashevskiy <aik@ozlabs.ru>,
 Rusty Russell <rusty@rustcorp.com.au>, Alexander Graf <agraf@suse.de>,
 kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org,
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On Wed, 2013-06-19 at 13:05 +0930, Rusty Russell wrote:
> symbol_get() won't try to load a module; it'll just fail.  This is what
> you want, since they must have vfio in the kernel to get a valid fd...

Ok, cool. I suppose what we want here Alexey is slightly higher level,
something like:

	vfio_validate_iommu_id(file, iommu_id)

Which verifies that the file that was passed in is allowed to use
that iommu_id.

That's a simple and flexible interface (ie, it will work even if we
support multiple iommu IDs in the future for a vfio, for example
for DDW windows etc...), the logic to know about the ID remains
in qemu, this is strictly a validation call.

That way we also don't have to expose the containing vfio struct etc...
just that simple function.

Alex, any objection ?

Do we need to make it a get/put interface instead ?

	vfio_validate_and_use_iommu(file, iommu_id);

	vfio_release_iommu(file, iommu_id);

To ensure that the resource remains owned by the process until KVM
is closed as well ?

Or do we want to register with VFIO with a callback so that VFIO can
call us if it needs us to give it up ?

Cheers,
Ben.