[dpdk-users] rte_virtio_pmd_init(): IOPL call failed - cannot use virtio PMD

[amit sehas]

I tried my best to make iopl work but couldnt, i wrote a small 'c' program that does only iopl()  and even that does not work, neither on the host machine nor on the VM in docker ... i am wondering if this has anything to do with bios settings ...i tried it on different machines too ... root permissions, explicity setting capset ... etc .. i tried them all but still does not work ... quite frustrating how many hours i had to spent trying different things...

thanks
 

    On Friday, August 3, 2018, 2:24:28 PM PDT, Stephen Hemminger <stephen at networkplumber.org> wrote:  
 
 On Wed, 1 Aug 2018 16:27:49 +0000 (UTC)
amit sehas <cun23 at yahoo.com> wrote:

> I am trying to run a dpdk application in docker and i get the above error ... the docker instance was run as below:
> 
> docker run -dit --name <name> -v /hostlibpath:/contlibpath:ro fedora:26 bash
> 
> i am new to dpdk, as a result i am quite lost as to where to look ...
> 
> thanks

Short answer virtio requires DPDK process to be run as root.

In order for the virtio device to signal the underlying host it may need the in/out instructions.
These CPU instructions are normally privileged (only allowed in kernel) but on Linux there is
is a system call to allow a process with root (really CAP_SYS_RAWIO) to do these from userspace.
See iopl manual page.

The actual answer is more complex. Older versions of virtio (legacy) use in/out but the
current version (modern) can use memory read/write.  Ideally, the DPDK virtio would only
ask for IOPL privilege if it needed it. The problem is that may need it during the negotiation
process. Someone should look into fixing this.