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

[Lu Baolu <baolu.lu@linux.intel.com>]

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(-)
>>
> 
> 
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