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

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Date:   Thu, 29 Aug 2019 09:43:31 +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 8/28/19 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 users that their active DMA mappings are no longer valid and they shouldn't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?

> Thanks,
> Janusz

Best regards,
Baolu