Re: [PATCH v6 0/9] vfio/mdev: IOMMU aware mediated device

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Hi Kirti,

On 2/15/19 4:14 AM, Alex Williamson wrote:
On Wed, 13 Feb 2019 12:02:52 +0800
Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> 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 one
new member 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.

Below helpers are added to set and get above iommu device 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.

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.

Below APIs are introduced in iommu generic layer for aux-domain
purpose:

* iommu_dev_has_feature(dev, IOMMU_DEV_FEAT_AUX)
   - Check whether both IOMMU and device support IOMMU aux
     domain feature. Below aux-domain specific interfaces
     are available only after this returns true.

* iommu_dev_enable/disable_feature(dev, IOMMU_DEV_FEAT_AUX)
   - Enable/disable device specific aux-domain feature.

* iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX)
   - Check whether the aux domain specific feature enabled or
     not.

* iommu_aux_attach_device(domain, dev)
   - Attaches @domain to @dev in the auxiliary mode. Multiple
     domains could be attached to a single device in the
     auxiliary mode with each domain representing an isolated
     address space for an assignable subset of the device.

* iommu_aux_detach_device(domain, dev)
   - Detach @domain which has been attached to @dev in the
     auxiliary mode.

* iommu_aux_get_pasid(domain, dev)
   - Return ID used for finer-granularity DMA translation.
     For the Intel Scalable IOV usage model, this will be
     a PASID. The device which supports Scalable IOV needs
     to write this ID to the device register so that DMA
     requests could be tagged with a right PASID prefix.

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 1/09~6/09)
adds the interfaces and implementation of the multiple domains per
device. The second part (PATCH 7/09~9/09) 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.

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

Best regards,
Lu Baolu

Change log:
   v5->v6:

This looks pretty reasonable with Jean-Philippe's nit fixups.  Where do
we go from here?  I think we need an ack from Kirti since they have an
interest here.  Presumably this looks ok to the ARM folks.  Do we have

Any comments?

Best regards,
Lu Baolu

any consumers of this code yet?  Theoretically I think a vfio-pci-like
meta driver could be written as an mdev vendor driver with this support
(restricted to type1 iommu use cases).  Thanks,

Alex




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