Please enable CONFIG_VFIO_NOIOMMU

[Christian Ehrhardt ]

Hi,
for certain cases a user might want to use VFIO in NO IOMMU mode.
This only enables it to be an option, it doesn't change things unless "enable_unsafe_noiommu_mode" is set. See this reference: https://patchwork.kernel.org/patch/7906971/ for more details.

This is used for some setups of DPDK see this http://dpdk-guide.gitlab.io/dpdk-guide/setup/binding.html#vfio-no-iommu

Usually the reason to pick vfio over uio is the isolation. But there are some cases where vfio is required for extra features but can't work unless NO-IOMMU mode is used.

I watched the topic a while checking if there is some major "oh crap what have we done" but there was none. An since by only enabling it in the kernel it shouldn't change a lot I wanted to ask if you could enable this config in the kernel for Z*.

Technically it would be nice to get it in Yakkety as well, but I think we should be fine only working forward and enabling it in the Z release.

[Christian Ehrhardt  (paelzer)]

Checks with DPDK waiting until a matching Kernel is available - incomplete until then.

[Brad Figg (brad-figg)]

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

apport-collect 1634050

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Christian Ehrhardt  (paelzer)]

No apport collect needed to discuss/enable this.

[Tim Gardner (timg-tpi)]

Christian - I'm not too keen on enabling this config. As you pointed out, it doesn't actually do anything without a kernel command line parameter. In the case where there truly is no IOMMU and enable_unsafe_noiommu_mode is set, then the kernel taint flag is also set.

Do you really think there is enough of a use case to warrant enabling this config ?

[Christian Ehrhardt  (paelzer)]

Hi Tim,
this was about being prepared. It can be solution to make things more accessible for experiments and development work as I stated initially. I'd never (hope to) expect it to be used in productive environments.

One might argue, that if someone wants to get that far he could also build his own kernel. But then you could say that to about everything we package :-)

So I thought since it really doesn't change anything without the kernel parm set we could provide it for the ease of Ubuntu users experimenting in that area.
It also can ease testing since your environment just doesn't have to have so much special HW constraints.
But if you still don't like it I can - for now - live with a refusal and we might wait until someone with a more tangible need for it comes up.