Re: [PATCH v2 0/8] Host1x context isolation support

[Robin Murphy]

On 2021-11-08 10:36, Mikko Perttunen wrote:
> On 9/16/21 5:32 PM, Mikko Perttunen wrote:
> > Hi all,
> >
> > ***
> > New in v2:
> >
> > Added support for Tegra194
> > Use standard iommu-map property instead of custom mechanism
> > ***
> >
> > this series adds support for Host1x 'context isolation'. Since
> > when programming engines through Host1x, userspace can program in
> > any addresses it wants, we need some way to isolate the engines'
> > memory spaces. Traditionally this has either been done imperfectly
> > with a single shared IOMMU domain, or by copying and verifying the
> > programming command stream at submit time (Host1x firewall).
> >
> > Since Tegra186 there is a privileged (only usable by kernel)
> > Host1x opcode that allows setting the stream ID sent by the engine
> > to the SMMU. So, by allocating a number of context banks and stream
> > IDs for this purpose, and using this opcode at the beginning of
> > each job, we can implement isolation. Due to the limited number of
> > context banks only each process gets its own context, and not
> > each channel.
> >
> > This feature also allows sharing engines among multiple VMs when
> > used with Host1x's hardware virtualization support - up to 8 VMs
> > can be configured with a subset of allowed stream IDs, enforced
> > at hardware level.
> >
> > To implement this, this series adds a new host1x context bus, which
> > will contain the 'struct device's corresponding to each context
> > bank / stream ID, changes to device tree and SMMU code to allow
> > registering the devices and using the bus, as well as the Host1x
> > stream ID programming code and support in TegraDRM.
> >
> > Device tree bindings are not updated yet pending consensus that the
> > proposed changes make sense.
> >
> > Thanks,
> > Mikko
> >
> > Mikko Perttunen (8):
> >    gpu: host1x: Add context bus
> >    gpu: host1x: Add context device management code
> >    gpu: host1x: Program context stream ID on submission
> >    iommu/arm-smmu: Attach to host1x context device bus
> >    arm64: tegra: Add Host1x context stream IDs on Tegra186+
> >    drm/tegra: falcon: Set DMACTX field on DMA transactions
> >    drm/tegra: vic: Implement get_streamid_offset
> >    drm/tegra: Support context isolation
> >
> >   arch/arm64/boot/dts/nvidia/tegra186.dtsi  |  12 ++
> >   arch/arm64/boot/dts/nvidia/tegra194.dtsi  |  12 ++
> >   drivers/gpu/Makefile                      |   3 +-
> >   drivers/gpu/drm/tegra/drm.h               |   2 +
> >   drivers/gpu/drm/tegra/falcon.c            |   8 +
> >   drivers/gpu/drm/tegra/falcon.h            |   1 +
> >   drivers/gpu/drm/tegra/submit.c            |  13 ++
> >   drivers/gpu/drm/tegra/uapi.c              |  34 ++++-
> >   drivers/gpu/drm/tegra/vic.c               |  38 +++++
> >   drivers/gpu/host1x/Kconfig                |   5 +
> >   drivers/gpu/host1x/Makefile               |   2 +
> >   drivers/gpu/host1x/context.c              | 174 ++++++++++++++++++++++
> >   drivers/gpu/host1x/context.h              |  27 ++++
> >   drivers/gpu/host1x/context_bus.c          |  31 ++++
> >   drivers/gpu/host1x/dev.c                  |  12 +-
> >   drivers/gpu/host1x/dev.h                  |   2 +
> >   drivers/gpu/host1x/hw/channel_hw.c        |  52 ++++++-
> >   drivers/gpu/host1x/hw/host1x06_hardware.h |  10 ++
> >   drivers/gpu/host1x/hw/host1x07_hardware.h |  10 ++
> >   drivers/iommu/arm/arm-smmu/arm-smmu.c     |  13 ++
> >   include/linux/host1x.h                    |  21 +++
> >   include/linux/host1x_context_bus.h        |  15 ++
> >   22 files changed, 488 insertions(+), 9 deletions(-)
> >   create mode 100644 drivers/gpu/host1x/context.c
> >   create mode 100644 drivers/gpu/host1x/context.h
> >   create mode 100644 drivers/gpu/host1x/context_bus.c
> >   create mode 100644 include/linux/host1x_context_bus.h
>
> IOMMU/DT folks, any thoughts about this approach? The patches that are 
> of interest outside of Host1x/TegraDRM specifics are patches 1, 2, 4, 
> and 5.

FWIW it looks fairly innocuous to me. I don't understand host1x - 
neither hardware nor driver abstractions - well enough to meaningfully 
review it all (e.g. maybe it's deliberate that the bus .dma_configure 
method isn't used?), but the SMMU patch seems fine given the Kconfig 
solution to avoid module linkage problems.

Cheers,
Robin.