[dpdk-dev] Issue with igb_uio in Fedora 24

["Mcnamara, John" <john.mcnamara@intel.com>]

Hi,

We have seen an issue when using the igb_uio module in Fedora
24. However, it relates to kernel 4.5+ so it could occur in other
distros/oses.

The issue occurs after binding a nic to igb_uio:

    # ./tools/dpdk_nic_bind.py -b igb_uio 0000:03:00.0
    # ./x86_64-native-linuxapp-gcc/app/test

    EAL: Detected 8 lcore(s)
    EAL: Probing VFIO support...
    PMD: bnxt_rte_pmd_init() called for (null)
    EAL: PCI device 0000:03:00.0 on NUMA socket -1
    EAL:   probe driver: 8086:1533 rte_igb_pmd
    EAL: pci_map_resource():
         cannot mmap(39, 0x7f1c51800000, 0x100000, 0x0):
         Invalid argument (0xffffffffffffffff)
    EAL: Error - exiting with code: 1
         Cause: Requested device 0000:03:00.0 cannot be used
    
The issue is exposed when the kernel is compiled with option
CONFIG_IO_STRICT_DEVMEM turned on.

This option is new from kernel 4.5 and is on by default in Fedora 24:

    config IO_STRICT_DEVMEM
        bool "Filter I/O access to /dev/mem"
        depends on STRICT_DEVMEM
        ---help---

          If this option is disabled, you allow userspace (root) access
          to all io-memory regardless of whether a driver is actively
          using that range.  Accidental access to this is obviously
          disastrous, but specific access can be used by people
          debugging kernel drivers.

          If this option is switched on, the /dev/mem file only allows
          userspace access to *idle* io-memory ranges (see /proc/iomem)
          This may break traditional users of /dev/mem (dosemu, legacy
          X, etc...)  if the driver using a given range cannot be
          disabled.

          If in doubt, say Y.

This issue doesn't occur with uio_pci_generic.

John