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

From: Lu Baolu
Date: Thu Aug 29 2019 - 05:09:39 EST


On 8/29/19 3:58 PM, Janusz Krzysztofik wrote:
Hi Baolu,

On Thursday, August 29, 2019 3:43:31 AM CEST Lu Baolu wrote:
Hi Janusz,

On 8/28/19 10:17 PM, Janusz Krzysztofik wrote:
We should avoid kernel panic when a intel_unmap() is called against
a non-existent domain.
Does that mean you suggest to replace
with something like
if (WARN_ON(!domain))
and to not care of orphaned mappings left allocated? Is there a way to
users that their active DMA mappings are no longer valid and they
call dma_unmap_*()?

But we shouldn't expect the IOMMU driver not
cleaning up the domain info when a device remove notification comes and
wait until all file descriptors being closed, right?
Shouldn't then the IOMMU driver take care of cleaning up resources still
allocated on device remove before it invalidates and forgets their

You are right. We need to wait until all allocated resources (iova and
mappings) to be released.

How about registering a callback for BUS_NOTIFY_UNBOUND_DRIVER, and
removing the domain info when the driver detachment completes?

Device core calls BUS_NOTIFY_UNBOUND_DRIVER on each driver unbind, regardless
of a device being removed or not. As long as the device is not unplugged and
the BUS_NOTIFY_REMOVED_DEVICE notification not generated, an unbound driver is
not a problem here.
Morever, BUS_NOTIFY_UNBOUND_DRIVER is called even before
BUS_NOTIFY_REMOVED_DEVICE so that wouldn't help anyway.
Last but not least, bus events are independent of the IOMMU driver use via
DMA-API it exposes.

Fair enough.

If keeping data for unplugged devices and reusing it on device re-plug is not
acceptable then maybe the IOMMU driver should perform reference counting of
its internal resources occupied by DMA-API users and perform cleanups on last

I am not saying that keeping data is not acceptable. I just want to
check whether there are any other solutions.

Best regards,