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

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Date:   Tue, 03 Sep 2019 09:41:23 +0200
From:   Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     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>,
        Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>
Subject: Re: [RFC PATCH] iommu/vt-d: Fix IOMMU field not populated on device hot re-plug

Hi Baolu,

On Tuesday, September 3, 2019 3:29:40 AM CEST Lu Baolu wrote:
> Hi Janusz,
> 
> On 9/2/19 4:37 PM, Janusz Krzysztofik wrote:
> >> I am not saying that keeping data is not acceptable. I just want to
> >> check whether there are any other solutions.
> > Then reverting 458b7c8e0dde and applying this patch still resolves the 
issue
> > for me.  No errors appear when mappings are unmapped on device close after 
the
> > device has been removed, and domain info preserved on device removal is
> > successfully reused on device re-plug.
> 
> This patch doesn't look good to me although I agree that keeping data is
> acceptable. It updates dev->archdata.iommu, but leaves the hardware
> context/pasid table unchanged. This might cause problems somewhere.
> 
> > 
> > Is there anything else I can do to help?
> 
> Can you please tell me how to reproduce the problem? 

The most simple way to reproduce the issue, assuming there are no non-Intel 
graphics adapters installed, is to run the following shell commands:

#!/bin/sh
# load i915 module
modprobe i915
# open an i915 device and keep it open in background
cat /dev/dri/card0 >/dev/null &
sleep 2
# simulate device unplug
echo 1 >/sys/class/drm/card0/device/remove
# make the background process close the device on exit
kill $!

Thanks,
Janusz


> Keeping the per
> device domain info while device is unplugged is a bit dangerous because
> info->dev might be a wild pointer. We need to work out a clean fix.
> 
> > 
> > Thanks,
> > Janusz
> > 
> 
> Best regards,
> Baolu
>