[dpdk-dev] [PATCH] eal: add option to force IOVA as PA mode

Chas Williams 3chas3 at gmail.com
Sun Dec 3 01:23:41 CET 2017

The particular machine in my case is a Dell Optiplex 790 which is fairly
similar to another system that has basically the same problem.  The IOMMU
advertises that is can only handle 39 bits of addressing.  The DMAR address
tables have a width of 36 bits, so all is well when using IOVA physical
addresses.  With IOVA virtual addresses, they sometimes go beyond the 39
bit boundary.  I was under the impression that IOMMU widths are more
typically 48 bits, but I appear to have some low end systems with a simpler

I could make it a runtime option.

On Thu, Nov 30, 2017 at 4:17 AM, Thomas Monjalon <thomas at monjalon.net>

> 30/11/2017 03:57, Chas Williams:
> > From: Chas Williams <chas3 at att.com>
> >
> > The IOMMU in some machines report that they can only support
> > limited widths.  IOVA virtual addresses may exceed this width
> > making the use of IOVA virtual addresses difficult.  The option
> > CONFIG_RTE_LIBRTE_USE_PHYS_IOVA can used to force IOVA physical
> > address usage.
> Which machines are you talking about?
> A run-time option may be a better solution.

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