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

From: Lu Baolu
Date: Wed Jan 01 2020 - 00:32:25 EST

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,

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(-)