Re: [dpdk-dev] Issue with igb_uio in Fedora 24

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 7/1/2016 11:21 AM, Mcnamara, John wrote:
> 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
> 


Thanks for Pablo figuring out the details, and related config option,
otherwise I was digging same issue without success.

Disabling following code in igb_uio makes it work again:
"pci_request_regions(dev, "igb_uio");"

This call adds device bars as active resources, and with above config
option mmap fails for those addresses.

uio_pci_generic already doesn't have this call, and I can send a patch
to remove this from igb_uio.

BUT, I don't know why that call added at first place and concerned about
any corner case that requires this call.
Anybody out has/knows a reason to keep this call?

Thanks,
ferruh