linux-kernel - Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling

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Date:	Wed, 19 Jun 2013 14:59:30 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Alexey Kardashevskiy <aik@...abs.ru>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Alexander Graf <agraf@...e.de>,
	Paul Mackerras <paulus@...ba.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling

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.

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