[RFC PATCH 0/4] iommu: Per-group default domain type

[Lu Baolu]

An IOMMU group represents the smallest set of devices that are considered
to be isolated. All devices belonging to an IOMMU group share a default
domain for DMA APIs. There are two types of default domain: IOMMU_DOMAIN_DMA
and IOMMU_DOMAIN_IDENTITY. The former means IOMMU translation, while the
latter means IOMMU by-pass.

Currently, the default domain type for the IOMMU groups is determined
globally. All IOMMU groups use a single default domain type. The global
default domain type can be adjusted by kernel build configuration or
kernel parameters.

More and more users are looking forward to a fine grained default domain
type. For example, with the global default domain type set to translation,
the OEM verndors or end users might want some trusted and fast-speed devices
to bypass IOMMU for performance gains. On the other hand, with global
default domain type set to by-pass, some devices with limited system
memory addressing capability might want IOMMU translation to remove the
bounce buffer overhead.

This series proposes per-group default domain type to meet these demands.
It adds a per-device iommu_passthrough attribute. By setting this
attribute, end users or device vendors are able to tell the IOMMU subsystem
that this device is willing to use a default domain of IOMMU_DOMAIN_IDENTITY.
The IOMMU device probe procedure is reformed to pre-allocate groups for
all devices on a specific bus before adding the devices into the groups.
This enables the IOMMU device probe precedure to determine a per-group
default domain type before allocating IOMMU domains and attaching them
to devices.

Please help to review it. Your comments and suggestions are appricated.

Best regards,
baolu 

Lu Baolu (4):
  driver core: Add iommu_passthrough to struct device
  PCI: Add "pci=iommu_passthrough=" parameter for iommu passthrough
  iommu: Preallocate iommu group when probing devices
  iommu: Determine default domain type before allocating domain

 .../admin-guide/kernel-parameters.txt         |   5 +
 drivers/iommu/iommu.c                         | 127 ++++++++++++++----
 drivers/pci/pci.c                             |  34 +++++
 drivers/pci/pci.h                             |   1 +
 drivers/pci/probe.c                           |   2 +
 include/linux/device.h                        |   3 +
 6 files changed, 143 insertions(+), 29 deletions(-)

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2.17.1