From: David Gibson <david@gibson.dropbear.id.au>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Alexander Graf <agraf@suse.de>,
linuxppc-dev@lists.ozlabs.org, Paul Mackerras <paulus@samba.org>,
"kvm@vger.kernel.org mailing list" <kvm@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
kvm-ppc@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling
Date: Mon, 24 Jun 2013 13:52:49 +1000 [thread overview]
Message-ID: <20130624035249.GD25265@voom.fritz.box> (raw)
In-Reply-To: <1371911286.30572.155.camel@ul30vt.home>
[-- Attachment #1: Type: text/plain, Size: 2795 bytes --]
On Sat, Jun 22, 2013 at 08:28:06AM -0600, Alex Williamson wrote:
> On Sat, 2013-06-22 at 22:03 +1000, David Gibson wrote:
> > On Thu, Jun 20, 2013 at 08:55:13AM -0600, Alex Williamson wrote:
> > > On Thu, 2013-06-20 at 18:48 +1000, Alexey Kardashevskiy wrote:
> > > > On 06/20/2013 05:47 PM, Benjamin Herrenschmidt wrote:
> > > > > On Thu, 2013-06-20 at 15:28 +1000, David Gibson wrote:
> > > > >>> Just out of curiosity - would not get_file() and fput_atomic() on a
> > > > >> group's
> > > > >>> file* do the right job instead of vfio_group_add_external_user() and
> > > > >>> vfio_group_del_external_user()?
> > > > >>
> > > > >> I was thinking that too. Grabbing a file reference would certainly be
> > > > >> the usual way of handling this sort of thing.
> > > > >
> > > > > But that wouldn't prevent the group ownership to be returned to
> > > > > the kernel or another user would it ?
> > > >
> > > >
> > > > Holding the file pointer does not let the group->container_users counter go
> > > > to zero
> > >
> > > How so? Holding the file pointer means the file won't go away, which
> > > means the group release function won't be called. That means the group
> > > won't go away, but that doesn't mean it's attached to an IOMMU. A user
> > > could call UNSET_CONTAINER.
> >
> > Uhh... *thinks*. Ah, I see.
> >
> > I think the interface should not take the group fd, but the container
> > fd. Holding a reference to *that* would keep the necessary things
> > around. But more to the point, it's the right thing semantically:
> >
> > The container is essentially the handle on a host iommu address space,
> > and so that's what should be bound by the KVM call to a particular
> > guest iommu address space. e.g. it would make no sense to bind two
> > different groups to different guest iommu address spaces, if they were
> > in the same container - the guest thinks they are different spaces,
> > but if they're in the same container they must be the same space.
>
> While the container is the gateway to the iommu, what empowers the
> container to maintain an iommu is the group. What happens to a
> container when all the groups are disconnected or closed? Groups are
> the unit that indicates hardware access, not containers. Thanks,
Uh... huh? I'm really not sure what you're getting at.
The operation we're doing for KVM here is binding a guest iommu
address space to a particular host iommu address space. Why would we
not want to use the obvious handle on the host iommu address space,
which is the container fd?
--
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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next prev parent reply other threads:[~2013-06-24 3:54 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-05 6:11 [PATCH 0/4 v3] KVM: PPC: IOMMU in-kernel handling Alexey Kardashevskiy
2013-06-05 6:11 ` [PATCH 1/4] KVM: PPC: Add support for multiple-TCE hcalls Alexey Kardashevskiy
2013-06-16 4:20 ` Benjamin Herrenschmidt
2013-06-16 22:06 ` Alexander Graf
2013-06-17 7:55 ` Alexey Kardashevskiy
2013-06-17 8:02 ` Alexander Graf
2013-06-17 8:34 ` Alexey Kardashevskiy
2013-06-17 8:40 ` Alexander Graf
2013-06-17 8:51 ` Alexey Kardashevskiy
2013-06-17 10:46 ` Alexander Graf
2013-06-17 10:48 ` Alexander Graf
2013-06-17 8:37 ` Benjamin Herrenschmidt
2013-06-17 8:42 ` Alexander Graf
2013-06-05 6:11 ` [PATCH 2/4] powerpc: Prepare to support kernel handling of IOMMU map/unmap Alexey Kardashevskiy
2013-06-16 4:26 ` Benjamin Herrenschmidt
2013-06-16 4:31 ` Benjamin Herrenschmidt
2013-06-17 9:17 ` Alexey Kardashevskiy
2013-06-05 6:11 ` [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling Alexey Kardashevskiy
2013-06-16 4:39 ` Benjamin Herrenschmidt
2013-06-19 3:17 ` Alexey Kardashevskiy
2013-06-16 22:25 ` Alexander Graf
2013-06-16 22:39 ` Benjamin Herrenschmidt
2013-06-17 3:13 ` Alex Williamson
2013-06-17 3:56 ` Benjamin Herrenschmidt
2013-06-18 2:32 ` Alex Williamson
2013-06-18 4:38 ` Benjamin Herrenschmidt
2013-06-18 14:48 ` Alex Williamson
2013-06-18 21:58 ` Benjamin Herrenschmidt
2013-06-19 3:35 ` Rusty Russell
2013-06-19 4:59 ` Benjamin Herrenschmidt
2013-06-19 9:58 ` Alexander Graf
2013-06-19 14:50 ` Benjamin Herrenschmidt
2013-06-19 15:49 ` Alex Williamson
2013-06-20 4:58 ` Alexey Kardashevskiy
2013-06-20 5:28 ` David Gibson
2013-06-20 7:47 ` Benjamin Herrenschmidt
2013-06-20 8:48 ` Alexey Kardashevskiy
2013-06-20 14:55 ` Alex Williamson
2013-06-22 8:25 ` Alexey Kardashevskiy
2013-06-22 12:03 ` David Gibson
2013-06-22 14:28 ` Alex Williamson
2013-06-24 3:52 ` David Gibson [this message]
2013-06-24 4:41 ` Alex Williamson
2013-06-27 11:01 ` David Gibson
2013-06-22 23:28 ` Benjamin Herrenschmidt
2013-06-24 3:54 ` David Gibson
2013-06-24 3:58 ` Benjamin Herrenschmidt
2013-06-05 6:11 ` [PATCH 4/4] KVM: PPC: Add hugepage " Alexey Kardashevskiy
2013-06-16 4:46 ` Benjamin Herrenschmidt
2013-06-17 16:35 ` Paolo Bonzini
2013-06-12 3:14 ` [PATCH 0/4 v3] KVM: PPC: " Benjamin Herrenschmidt
-- strict thread matches above, loose matches on Subject: below --
2013-05-21 3:06 [PATCH 0/4 v2] " Alexey Kardashevskiy
2013-05-21 3:06 ` [PATCH 3/4] KVM: PPC: Add support for " Alexey Kardashevskiy
2013-05-22 21:06 ` Scott Wood
2013-05-25 2:45 ` David Gibson
2013-05-27 2:44 ` Alexey Kardashevskiy
2013-05-28 17:45 ` Scott Wood
2013-05-28 23:30 ` Alexey Kardashevskiy
2013-05-28 23:35 ` Scott Wood
2013-05-29 0:12 ` Alexey Kardashevskiy
2013-05-29 20:05 ` Scott Wood
2013-05-29 23:10 ` Alexey Kardashevskiy
2013-05-29 23:14 ` Scott Wood
2013-05-29 23:29 ` Alexey Kardashevskiy
2013-05-29 23:32 ` Scott Wood
2013-05-27 10:23 ` Paolo Bonzini
2013-05-27 14:26 ` Alexey Kardashevskiy
2013-05-27 14:41 ` Paolo Bonzini
2013-05-28 16:32 ` Scott Wood
2013-05-29 0:20 ` Alexey Kardashevskiy
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