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

[Lu Baolu]

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 at linux.intel.com>
Date:   Thu Aug 1 11:14:58 2019 +0800

     iommu/vt-d: Detach domain when move device out of group

     When removing a device from an iommu group, the domain should
     be detached from the device. Otherwise, the stale domain info
     will still be cached by the driver and the driver will refuse
     to attach any domain to the device again.

     Cc: Ashok Raj <ashok.raj at intel.com>
     Cc: Jacob Pan <jacob.jun.pan at linux.intel.com>
     Cc: Kevin Tian <kevin.tian at intel.com>
     Fixes: b7297783c2bb6 ("iommu/vt-d: Remove duplicated code for 
device hotplug")
     Reported-and-tested-by: Vlad Buslov <vladbu at mellanox.com>
     Suggested-by: Robin Murphy <robin.murphy at arm.com>
     Link: https://lkml.org/lkml/2019/7/26/1133
     Signed-off-by: Lu Baolu <baolu.lu at linux.intel.com>
     Signed-off-by: Joerg Roedel <jroedel at suse.de>

Best regards,
Lu Baolu

> 
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
> ---
>   drivers/iommu/intel-iommu.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 12d094d08c0a..7cdcd0595408 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2477,6 +2477,9 @@ static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
>   		if (info2) {
>   			found      = info2->domain;
>   			info2->dev = dev;
> +
> +			if (dev && !dev->archdata.iommu)
> +				dev->archdata.iommu = info2;
>   		}
>   	}
>   
>