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doc: add known issue for iommu and igb_uio

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Known issue regarding iommu/VT-d and igb_uio in Linux kernel version 3.15
to 3.17 where unbinding the device from the driver removes the 1:1 mapping
in the iommu resulting in IOMMU/DMAR errors when the device tries to
access memory.

Signed-off-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>
This commit is contained in:
Sergio Gonzalez Monroy 2014-12-15 10:32:43 +00:00 committed by Thomas Monjalon
parent 048f830326
commit 7547be1efc
1 changed files with 32 additions and 0 deletions
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32
doc/guides/rel_notes/known_issues.rst
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@ -777,3 +777,35 @@ Stopping the port does not down the link on Intel® 40G ethernet controller
| Driver/Module | Poll Mode Driver (PMD) |
| | |
+--------------------------------+--------------------------------------------------------------------------------------+
Devices bound to igb_uio with VT-d enabled do not work on Linux* kernel 3.15-3.17
---------------------------------------------------------------------------------
+--------------------------------+--------------------------------------------------------------------------------------+
| Title | Devices bound to igb_uio with VT-d enabled do not work on Linux* kernel 3.15-3.17 |
+================================+======================================================================================+
| Description | | When VT-d is enabled (iommu=pt intel_iommu=on), devices are 1:1 mapped. |
| | In the Linux* kernel unbinding devices from drivers removes that mapping which |
| | result in IOMMU errors. |
| | | Introduced in Linux `kernel 3.15 commit <https://git.kernel.org/cgit/linux/kernel/ |
| | git/torvalds/linux.git/commit/drivers/iommu/ |
| | intel-iommu.c?id=816997d03bca9fabcee65f3481eb0297103eceb7>`_, |
| | solved in Linux `kernel 3.18 commit <https://git.kernel.org/cgit/linux/kernel/git/ |
| | torvalds/linux.git/commit/drivers/iommu/ |
| | intel-iommu.c?id=1196c2fb0407683c2df92d3d09f9144d42830894>`_. |
+--------------------------------+--------------------------------------------------------------------------------------+
| Implication | | Devices will not be allowed to access memory, resulting in following kernel errors:|
| | | ``dmar: DRHD: handling fault status reg 2`` |
| | | ``dmar: DMAR:[DMA Read] Request device [02:00.0] fault addr a0c58000`` |
| | | ``DMAR:[fault reason 02] Present bit in context entry is clear`` |
+--------------------------------+--------------------------------------------------------------------------------------+
| Resolution/ Workaround | | Use earlier or later kernel versions, or avoid driver binding on boot by |
| | blacklisting the driver modules. |
| | | ie. in the case of ixgbe, we can pass the kernel command line option: |
| | | ``modprobe.blacklist=ixgbe`` |
| | | This way we do not need to unbind the device to bind it to igb_uio. |
+--------------------------------+--------------------------------------------------------------------------------------+
| Affected Environment/ Platform | Linux* systems with kernel versions 3.15 to 3.17 |
+--------------------------------+--------------------------------------------------------------------------------------+
| Driver/Module | igb_uio module |
+--------------------------------+--------------------------------------------------------------------------------------+