[PATCH v3 0/8] vfio/mdev: IOMMU aware mediated device

Lu Baolu
2018-10-12T05:16:24Z

Hi,

The Mediate Device is a framework for fine-grained physical device
sharing across the isolated domains. Currently the mdev framework
is designed to be independent of the platform IOMMU support. As the
result, the DMA isolation relies on the mdev parent device in a
vendor specific way.

There are several cases where a mediated device could be protected
and isolated by the platform IOMMU. For example, Intel vt-d rev3.0
[1] introduces a new translation mode called 'scalable mode', which
enables PASID-granular translations. The vt-d scalable mode is the
key ingredient for Scalable I/O Virtualization [2] [3] which allows
sharing a device in minimal possible granularity (ADI - Assignable
Device Interface).

A mediated device backed by an ADI could be protected and isolated
by the IOMMU since 1) the parent device supports tagging an unique
PASID to all DMA traffic out of the mediated device; and 2) the DMA
translation unit (IOMMU) supports the PASID granular translation.
We can apply IOMMU protection and isolation to this kind of devices
just as what we are doing with an assignable PCI device.

In order to distinguish the IOMMU-capable mediated devices from those
which still need to rely on parent devices, this patch set adds two
new members in struct mdev_device.

* iommu_device
- This, if set, indicates that the mediated device could
be fully isolated and protected by IOMMU via attaching
an iommu domain to this device. If empty, it indicates
using vendor defined isolation.

* iommu_domain
- This is a place holder for an iommu domain. A domain
could be store here for later use once it has been
attached to the iommu_device of this mdev.

Below helpers are added to set and get above iommu device
and iommu domain pointers in mdev core implementation.

* mdev_set/get_iommu_device(dev, iommu_device)
- Set or get the iommu device which represents this mdev
in IOMMU's device scope. Drivers don't need to set the
iommu device if it uses vendor defined isolation.

* mdev_set/get_iommu_domain(domain)
- A iommu domain which has been attached to the iommu
device in order to protect and isolate the mediated
device will be kept in the mdev data structure and
could be retrieved later.

The mdev parent device driver could opt-in that the mdev could be
fully isolated and protected by the IOMMU when the mdev is being
created by invoking mdev_set_iommu_device() in its @create().

In the vfio_iommu_type1_attach_group(), a domain allocated through
iommu_domain_alloc() will be attached to the mdev iommu device if
an iommu device has been set. Otherwise, the dummy external domain
will be used and all the DMA isolation and protection are routed to
parent driver as the result.

On IOMMU side, a basic requirement is allowing to attach multiple
domains to a PCI device if the device advertises the capability
and the IOMMU hardware supports finer granularity translations than
the normal PCI Source ID based translation.

As the result, a PCI device could work in two modes: normal mode
and auxiliary mode. In the normal mode, a pci device could be
isolated in the Source ID granularity; the pci device itself could
be assigned to a user application by attaching a single domain
to it. In the auxiliary mode, a pci device could be isolated in
finer granularity, hence subsets of the device could be assigned
to different user level application by attaching a different domain
to each subset.

The device driver is able to switch between above two modes with
below interfaces:

* iommu_get_dev_attr(dev, IOMMU_DEV_ATTR_AUXD_CAPABILITY)
- Represents the ability of supporting multiple domains
per device.

* iommu_set_dev_attr(dev, IOMMU_DEV_ATTR_AUXD_ENABLE)
- Enable the multiple domains capability for the device
referenced by @dev.

* iommu_set_dev_attr(dev, IOMMU_DEV_ATTR_AUXD_DISABLE)
- Disable the multiple domains capability for the device
referenced by @dev.

* iommu_domain_get_attr(domain, DOMAIN_ATTR_AUXD_ID)
- Return ID used for finer-granularity DMA translation.

The existing interfaces for attaching/detaching domains keep the
same as before. The different behaviors between the normal mode
and the auxiliary mode are handled in the vendor specific iommu
drivers.

In order for the ease of discussion, sometimes we call "a domain in
auxiliary mode' or simply 'an auxiliary domain' when a domain is
attached to a device for finer granularity translations. But we need
to keep in mind that this doesn't mean there is a differnt domain
type. A same domain could be bound to a device for Source ID based
translation, and bound to another device for finer granularity
translation at the same time.

This patch series extends both IOMMU and vfio components to support
mdev device passing through when it could be isolated and protected
by the IOMMU units. The first part of this series (PATCH 1/08~5/08)
adds the interfaces and implementation of the multiple domains per
device. The second part (PATCH 6/08~8/08) adds the iommu device
attribute to each mdev, determines isolation type according to the
existence of an iommu device when attaching group in vfio type1 iommu
module, and attaches the domain to iommu aware mediated devices.

This patch series depends on a patch set posted here [4] for discussion
which added scalable mode support in Intel IOMMU driver.

References:
[1] https://software.intel.com/en-us/download/intel-virtualization-technology-for-directed-io-architecture-specification
[2] https://software.intel.com/en-us/download/intel-scalable-io-virtualization-technical-specification
[3] https://schd.ws/hosted_files/lc32018/00/LC3-SIOV-final.pdf
[4] https://lkml.org/lkml/2018/10/7/54

Best regards,
Lu Baolu

Change log:
v2->v3:
- Remove domain type enum and use a pointer on mdev_device instead.
- Add a generic interface for getting/setting per device iommu
attributions. And use it for query aux domain capability, enable
aux domain and disable aux domain purpose.
- Reuse iommu_domain_get_attr() to retrieve the id in a aux domain.
- We discussed the impact of the default domain implementation
on reusing iommu_at(de)tach_device() interfaces. We agreed
that reusing iommu_at(de)tach_device() interfaces is the right
direction and we could tweak the code to remove the impact.
https://www.spinics.net/lists/kvm/msg175285.html
- Removed the RFC tag since no objections received.
- This patch has been submitted separately.
https://www.spinics.net/lists/kvm/msg173936.html

v1->v2:
- Rewrite the patches with the concept of auxiliary domains.

Lu Baolu (8):
iommu: Add APIs for multiple domains per device
iommu/vt-d: Add multiple domains per device query
iommu/vt-d: Enable/disable multiple domains per device
iommu/vt-d: Attach/detach domains in auxiliary mode
iommu/vt-d: Return ID associated with an auxiliary domain
vfio/mdev: Add iommu place holders in mdev_device
vfio/type1: Add domain at(de)taching group helpers
vfio/type1: Handle different mdev isolation type

drivers/iommu/intel-iommu.c | 249 ++++++++++++++++++++++++++++++-
drivers/iommu/iommu.c | 25 ++++
drivers/vfio/mdev/mdev_core.c | 36 +++++
drivers/vfio/mdev/mdev_private.h | 2 +
drivers/vfio/vfio_iommu_type1.c | 146 ++++++++++++++++--
include/linux/intel-iommu.h | 11 ++
include/linux/iommu.h | 33 ++++
include/linux/mdev.h | 23 +++
8 files changed, 509 insertions(+), 16 deletions(-)

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2.17.1