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

[Xu Zaibo]

Hi,

On 2018/10/12 13:16, 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().
I just cannot understand here, how to get an iommu_device while I create 
mediated
device in my parent device driver?

And why not reuse the device of MDEV instread of adding a new device here?

Thanks,
Zaibo

.
> 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(-)