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

[Stephen Hemminger]

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.