Re: [PATCH v4 0/8] vfio/mdev: IOMMU aware mediated device

From: Lu Baolu
Date: Tue Dec 04 2018 - 01:23:13 EST

Hi,

On 12/4/18 11:46 AM, Xu Zaibo wrote:
Hi,

Is this solution trying to support general user space processes who are directly working on devices?

Yes, it is.


Thanks,
Zaibo

Best regards,
Lu Baolu


.

On 2018/11/5 15:34, Lu Baolu wrote:
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.

* iommu_attach_device_aux(domain, dev)
   - Attach a domain to the device in the auxiliary mode.

* iommu_detach_device_aux(domain, dev)
   - Detach the aux domain from device.

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/2018/11/5/136

Best regards,
Lu Baolu

Change log:
   v3->v4:
   - Use aux domain specific interfaces for domain attach and detach.
   - Rebase all patches to 4.20-rc1.

   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      | 315 ++++++++++++++++++++++++++++---
  drivers/iommu/iommu.c            |  52 +++++
  drivers/vfio/mdev/mdev_core.c    |  36 ++++
  drivers/vfio/mdev/mdev_private.h |   2 +
  drivers/vfio/vfio_iommu_type1.c  | 162 ++++++++++++++--
  include/linux/intel-iommu.h      |  11 ++
  include/linux/iommu.h            |  52 +++++
  include/linux/mdev.h             |  23 +++
  8 files changed, 618 insertions(+), 35 deletions(-)