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

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Date:   Mon, 26 Aug 2019 16:29:12 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Michał Wajdeczko <michal.wajdeczko@...el.com>
Subject: Re: [RFC PATCH] iommu/vt-d: Fix IOMMU field not populated on device
 hot re-plug

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:
>> Hi,
>>
>> 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 <baolu.lu@...ux.intel.com>
>> 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