[SOLVED] Dell E6510, intel_iommu=on causes hang during boot

gemarcano · Last edited by gemarcano on Fri May 16, 2014 12:55 pm; edited 1 time in total

I am trying to get PCI passthrough to work on a Dell Latitude E6510 without success. I understand I need to have IOMMU enabled in order to do so. After enabling it in the kernel (and disabling it by default), I can boot the computer fine and OpenRC finishes starting all services fine. When booting, if I modify the kernel parameters to include intel_iommu=on , the OpenRC service starting step hangs at random-ish sections, but no later than "Wiping /tmp directory". I disabled, in rc.conf, parallel service starting to make sure that wasn't a problem. When the system hangs, Ctrl-alt-del does nothing, and the system does not respond to sysreq commands. I see no output of the kernel panicking or crashing with an Oops, so I have no clue as to what is going on. Does anyone have any idea as to what could be going on? What kind of logs should I be looking for? I haven't done in-depth kernel debugging before, so I'm not sure how to use things like netconsole to capture debugging information. As soon as I can get a netconsole log, though, I'll post it up.

With regards to system information, the computer in question is a Dell Latitude E6510, i7 740Q with 8 GB of RAM. It is running Gentoo ~amd64 with OpenRC as the init system, and KDE as the display manager. The kernel is 3.14.4. The kernel config is here on Pastebin.

EDIT: emerge --info:

chithanh · Posted: Thu May 15, 2014 1:55 pm Post subject:

intel_iommu is known to cause problems with nvidia graphics cards. If your laptop has switchable graphics/Optimus, can you try to turn off the nvidia graphics?

Apart from that, you can check if there is a BIOS upgrade available.

Logicien · Posted: Thu May 15, 2014 7:06 pm Post subject:

I was not able to boot with my personnal kernel configuration of the gentoo-sources on an Intel(R) Core(TM)2 Duo CPU E6550 @ 2.33GHz, where iommu is enable by default. Passing the kernel parameter

gemarcano · Posted: Thu May 15, 2014 8:17 pm Post subject:

@chithanh
I upgraded to newest BIOS/UEFI for this laptop system but it did not help. The laptop does have an NVidia card (a rather old one), so I will be trying disabling it in the near future (UEFI/BIOS setup does not have an option to turn it off). Currently lspci is not returning anything about an Intel VGA or video controller, so it makes me wonder if I have Intel integrated graphics available. I could have just forgotten to enable it in the kernel and as such lspci fails to pick it up. Maybe.

@Logicien
I tried your suggestion of intel_iommu=igfx_off, but it did not work... I wonder if it has something to do with the fact I'm using UEFI and not BIOS? Thanks for the suggestion, though.

I'll keep poking at this as I have time. I guess next on the list of things to get is an actual netconsole log output and maybe enable more debugging output from the kernel. Thanks for the help!

gemarcano · Posted: Fri May 16, 2014 12:54 pm Post subject:

I still don't have a netconsole output, but I do have something new. I booted the laptop this morning with intel_iommu enabled, and it didn't quite crash, but it wasn't advancing in the boot process. I started to give it Sysrq commands to reboot, and one of them, I think Alt-Sysrq-e, triggered a massive onslaught of messages on my screen. I was able to capture a photo on my phone (scroll lock wasn't working, and any further Sysrq commands were being ignored) and I was able to read the messages: