[DPDK/vhost/virtio Bug 1642] Devices bound to igb_uio with VT-d enabled do not work on Linux kernel 3.15-3.17

[bugzilla@dpdk.org]

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https://bugs.dpdk.org/show_bug.cgi?id=1642

            Bug ID: 1642
           Summary: Devices bound to igb_uio with VT-d enabled do not work
                    on Linux kernel 3.15-3.17
           Product: DPDK
           Version: unspecified
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: vhost/virtio
          Assignee: dev@dpdk.org
          Reporter: nandinipersad361@gmail.com
  Target Milestone: ---

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, solved in Linux kernel
3.18 commit.

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. I.e., 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.

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