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SubjectRe: [RFC PATCH] iommu/vt-d: Fix IOMMU field not populated on device hot re-plug
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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
> > BUG_ON(!domain);
> > with something like
> > if (WARN_ON(!domain))
> > return;
> > and to not care of orphaned mappings left allocated? Is there a way to
inform
> > users that their active DMA mappings are no longer valid and they
shouldn't
> > 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
pointers?
> >
>
> 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.

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
release?

Thanks,
Janusz


> > Thanks,
> > Janusz
>
> Best regards,
> Baolu
>




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