Re: [RFC PATCH] iommu/vt-d: Fix IOMMU field not populated on device hot re-plug

From: Lu Baolu
Date: Mon Aug 26 2019 - 04:30:29 EST

Hi Janusz,

On 8/26/19 4:15 PM, Janusz Krzysztofik wrote:
Hi Lu,

On Friday, August 23, 2019 3:51:11 AM CEST Lu Baolu wrote:

On 8/22/19 10:29 PM, Janusz Krzysztofik wrote:
When a perfectly working i915 device is hot unplugged (via sysfs) and
hot re-plugged again, its dev->archdata.iommu field is not populated
again with an IOMMU pointer. As a result, the device probe fails on
DMA mapping error during scratch page setup.

It looks like that happens because devices are not detached from their
MMUIO bus before they are removed on device unplug. Then, when an
already registered device/IOMMU association is identified by the
reinstantiated device's bus and function IDs on IOMMU bus re-attach
attempt, the device's archdata is not populated with IOMMU information
and the bad happens.

I'm not sure if this is a proper fix but it works for me so at least it
confirms correctness of my analysis results, I believe. So far I
haven't been able to identify a good place where the possibly missing
IOMMU bus detach on device unplug operation could be added.

Which kernel version are you testing with? Does it contain below commit?

commit 458b7c8e0dde12d140e3472b80919cbb9ae793f4
Author: Lu Baolu <>
Date: Thu Aug 1 11:14:58 2019 +0800

I was using an internal branch based on drm-tip which didn't contain this
commit yet. Fortunately it has been already merged into drm-tip over last
weekend and has effectively fixed the issue.

Thanks for testing this.

Best regards,
Lu Baolu