Message-ID: <1371530335.21896.169.camel@pasglop>
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>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>, linuxppc-dev@lists.ozlabs.org,
        David Gibson <david@gibson.dropbear.id.au>,
        Alexander Graf <agraf@suse.de>, Paul Mackerras <paulus@samba.org>,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm-ppc@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 18 Jun 2013 14:38:55 +1000
In-Reply-To: <1371522772.22681.140.camel@ul30vt.home>
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On Mon, 2013-06-17 at 20:32 -0600, Alex Williamson wrote:

> Right, we don't want to create dependencies across modules.  I don't
> have a vision for how this should work.  This is effectively a complete
> side-band to vfio, so we're really just dealing in the iommu group
> space.  Maybe there needs to be some kind of registration of ownership
> for the group using some kind of token.  It would need to include some
> kind of notification when that ownership ends.  That might also be a
> convenient tag to toggle driver probing off for devices in the group.
> Other ideas?  Thanks,

All of that smells nasty like it will need a pile of bloody
infrastructure.... which makes me think it's too complicated and not the
right approach.

How does access control work today on x86/VFIO ? Can you give me a bit
more details ? I didn't get a good grasp in your previous email....

>From the look of it, the VFIO file descriptor is what has the "access
control" to the underlying iommu, is this right ? So we somewhat need to
transfer (or copy) that ownership from the VFIO fd to the KVM VM.

I don't see a way to do that without some cross-layering here...

Rusty, are you aware of some kernel mechanism we can use for that ?

Cheers,
Ben.


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