Re: [dpdk-dev] Running DPDK as an unprivileged user

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 29 Dec 2016 20:41:21 +0000
"Walker, Benjamin" <benjamin.walker@intel.com> wrote:

> The first open question I have is whether DPDK should allow
> uio at all on recent (4.x) kernels. My current understanding
> is that there is no way to pin memory and hugepages can now
> be moved around, so uio would be unsafe. What does the
> community think here?

DMA access without IOMMU (ie UIO) is not safe from a security
point of view. A malicious app could program device (like Ethernet
NIC) to change its current privledge level in kernel memory.
Therefore ignore UIO as an option if you want to allow unprivileged
access.

But there are many many systems without working IOMMU. Not just broken
motherboards, but virtualization environments (Xen, Hyper-V, and KVM until
very recently) where IOMMU is no going to work.  In these environments,
DPDK is still useful where the security risks are known.

If kernel broke pinning of hugepages, then it is an upstream kernel bug.

> 
> My second question is whether the user should be allowed to
> mix uio and vfio usage simultaneously. For vfio, the
> physical addresses are really DMA addresses and are best
> when arbitrarily chosen to appear sequential relative to
> their virtual addresses. For uio, they are physical
> addresses and are not chosen at all. It seems that these two
> things are in conflict and that it will be difficult, ugly,
> and maybe impossible to resolve the simultaneous use of
> both.

Unless application is running as privileged user (ie root), UIO
is not going to work. Therefore don't worry about mixed environment.