RE: [RFC][PATCH] Remove bus dependency for iommu_domain_alloc.
From: Varun Sethi
Date: Fri Jan 17 2014 - 15:21:45 EST
> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Saturday, January 18, 2014 1:39 AM
> To: Sethi Varun-B16395
> Cc: joro@xxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-
> Subject: Re: [RFC][PATCH] Remove bus dependency for iommu_domain_alloc.
> On Sat, 2014-01-18 at 01:00 +0530, Varun Sethi wrote:
> > This patch attempts to remove iommu_domain_alloc function's dependency
> on the bus type.
> > This dependency is quiet restrictive in case of vfio, where it's
> > possible to bind multiple iommu groups (from different bus types) to
> the same iommu domain.
> > This patch is based on the assumption, that there is a single iommu
> > for all bus types on the system.
> > We maintain a list of bus types (for which iommu ops are registered).
> > In the iommu_domain_alloc function we ensure that all bus types
> correspond to the same set of iommu operations.
> Seems like this just kicks the problem down the road a little ways as I
> expect the assumption isn't going to last long. I think there's another
> way to do this and we can do it entirely from within vfio_iommu_type1.
> We have a problem on x86 that the IOMMU driver can be backed by multiple
> IOMMU hardware devices. These separate devices are architecturally
> allowed to have different properties. The property causing us trouble is
> cache coherency. Some hardware devices allow us to use IOMMU_CACHE as a
> mapping attribute, others do not. Therefore we cannot use a single IOMMU
> domain to optimally handle all devices in a heterogeneous environment.
> I think the solution to this is to have vfio_iommu_type1 transparently
> support multiple IOMMU domains. In the implementation of that, it seems
> to make sense to move the iommu_domain_alloc() to the point where we
> attach a group to the domain. That means we can scan the devices in the
[Sethi Varun-B16395] Multiple iommu groups can also share the same domain (as a part
Of the same VFIO container). I am not sure how can we handle the case of iommu groups from
Different bus types in vfio.
> domain to determine the bus. I suppose there is still an assumption that
> all the devices in a group are on the same bus, but since the group is
> determined by the IOMMU and we already assume only a single IOMMU per
> bus, I think we're ok. I spent some time working on a patch to do this,
> but it isn't quite finished. I'll try to bandage the rough edges and
> send it out as an RFC so you can see what I'm talking about. Thanks,
> > Signed-off-by: Varun Sethi <Varun.Sethi@xxxxxxxxxxxxx>
> > ---
> > arch/arm/mm/dma-mapping.c | 2 +-
> > drivers/gpu/drm/msm/msm_gpu.c | 2 +-
> > drivers/iommu/amd_iommu_v2.c | 2 +-
> > drivers/iommu/iommu.c | 32
> > drivers/media/platform/omap3isp/isp.c | 2 +-
> > drivers/remoteproc/remoteproc_core.c | 2 +-
> > drivers/vfio/vfio_iommu_type1.c | 2 +-
> > include/linux/device.h | 2 ++
> > include/linux/iommu.h | 4 ++--
> > virt/kvm/iommu.c | 2 +-
> > 10 files changed, 40 insertions(+), 12 deletions(-)