2017-04-03 04:58:01 +08:00
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=====================================
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The Linux kernel user-space API guide
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=====================================
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.. _man-pages: https://www.kernel.org/doc/man-pages/
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While much of the kernel's user-space API is documented elsewhere
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(particularly in the man-pages_ project), some user-space information can
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also be found in the kernel tree itself. This manual is intended to be the
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place where this information is gathered.
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.. class:: toc-title
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Table of contents
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.. toctree::
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:maxdepth: 2
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2017-05-13 19:51:38 +08:00
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no_new_privs
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2017-05-13 19:51:37 +08:00
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seccomp_filter
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2017-04-03 05:18:32 +08:00
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unshare
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2018-04-29 21:20:11 +08:00
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spec_ctrl
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2019-06-18 22:39:21 +08:00
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accelerators/ocxl
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ioasid: Add /dev/ioasid for userspace
commit ff6ff5e316b6bd83ea35dff8d88e7a3daa4000de Intel-BKC.
I/O Address Space IDs (IOASIDs) is used to tag DMA requests to target
multiple DMA address spaces for physical devices. Its PCI terminology
is called PASID (Process Address Space ID). Platforms with PASID support
can provide PASID granularity DMA isolation, which is very useful for
efficient and secure device sharing (SVA, subdevice passthrough, etc.).
Today only kernel drivers are allowed to allocate IOASIDs [1]. This patch
aims to extend this capability to userspace as required in device pass-
through scenarios. For example, a userspace driver may want to create its
own DMA address spaces besides the default IOVA address space established
by the kernel on the assigned device (e.g. vDPA control vq [2] and guest
SVA [3]), thus need to get IOASIDs from the kernel IOASID allocator for
tagging. In concept, each device can have its own IOASID space, thus it's
also possible for userspace driver to manage a private IOASID space itself,
say, when PF/VF is assigned. However it doesn't work for subdevice pass-
through, as multiple subdevices under the same parent device share a single
IOASID space thus IOASIDs must be centrally managed by the kernel in such
case.
This patch introduces a /dev/ioasid interface for this purpose (per discussion
in [4]). An IOASID is just a number before it is tagged to a specific DMA
address space. The actual IOASID tagging (to DMA requests) and association
(with DMA address spaces) operations from userspace are scrutinized by specific
device passthrough frameworks, which must ensure that a malicious driver
cannot program arbitrary IOASIDs to its assigned device to access DMA address
spaces that don't belong to it, this is out of the scope of this patch (a
reference VFIO implementation will be posted soon).
Open:
PCIe PASID is 20bit implying a space with 1M IOASIDs. although it's plenty
there was an open [4] on whether this user interface is open to all processes
or only selective processes (e.g. with device assigned). In this patchseries,
a cgroup controller is introduced to manage IOASID quota that a process is
allowed to use. A cgroup-enabled system may by default set quota=0 to disallow
IOASID allocation for most processes, and then having the virt management
stack to adjust the quota for a process which gets device assigned. But yeah,
we are also willing to hear more suggestions.
[1] https://lore.kernel.org/linux-iommu/1565900005-62508-8-git-send-email-jacob.jun.pan@linux.intel.com/
[2] https://lore.kernel.org/kvm/20201216064818.48239-1-jasowang@redhat.com/
[3] https://lore.kernel.org/linux-iommu/1599734733-6431-1-git-send-email-yi.l.liu@intel.com/
[4] https://lore.kernel.org/kvm/20201014171055.328a52f4@w520.home/
Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
Signed-off-by: Chen Zhuo <sagazchen@tencent.com>
Signed-off-by: Xinghui Li <korantli@tencent.com>
2022-06-01 14:38:31 +08:00
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ioasid
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2017-04-03 05:18:32 +08:00
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2017-04-03 04:58:01 +08:00
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.. only:: subproject and html
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Indices
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=======
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* :ref:`genindex`
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