linux-kernel - Re: [PATCH 03/10] vfio: add external user support

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Date:	Mon, 05 Aug 2013 11:18:12 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Paul Mackerras <paulus@...ba.org>,
	Alexander Graf <agraf@...e.de>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 03/10] vfio: add external user support

On Tue, 2013-07-23 at 19:07 +1000, Alexey Kardashevskiy wrote:
> On 07/23/2013 12:23 PM, Alex Williamson wrote:
> > On Tue, 2013-07-16 at 10:53 +1000, Alexey Kardashevskiy wrote:
> >> VFIO is designed to be used via ioctls on file descriptors
> >> returned by VFIO.
> >>
> >> However in some situations support for an external user is required.
> >> The first user is KVM on PPC64 (SPAPR TCE protocol) which is going to
> >> use the existing VFIO groups for exclusive access in real/virtual mode
> >> on a host to avoid passing map/unmap requests to the user space which
> >> would made things pretty slow.
> >>
> >> The protocol includes:
> >>
> >> 1. do normal VFIO init operation:
> >> 	- opening a new container;
> >> 	- attaching group(s) to it;
> >> 	- setting an IOMMU driver for a container.
> >> When IOMMU is set for a container, all groups in it are
> >> considered ready to use by an external user.
> >>
> >> 2. User space passes a group fd to an external user.
> >> The external user calls vfio_group_get_external_user()
> >> to verify that:
> >> 	- the group is initialized;
> >> 	- IOMMU is set for it.
> >> If both checks passed, vfio_group_get_external_user()
> >> increments the container user counter to prevent
> >> the VFIO group from disposal before KVM exits.
> >>
> >> 3. The external user calls vfio_external_user_iommu_id()
> >> to know an IOMMU ID. PPC64 KVM uses it to link logical bus
> >> number (LIOBN) with IOMMU ID.
> >>
> >> 4. When the external KVM finishes, it calls
> >> vfio_group_put_external_user() to release the VFIO group.
> >> This call decrements the container user counter.
> >> Everything gets released.
> >>
> >> The "vfio: Limit group opens" patch is also required for the consistency.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
> > 
> > This looks fine to me.  Is the plan to add this through the ppc tree
> > again?  Thanks,
> 
> 
> Nope, better to add this through your tree. And faster for sure :) Thanks!

Applied to my next branch for v3.12.  Thanks,

Alex


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