Re: [PATCH v4 08/18] iommu/vt-d: Clear unpreserved context entries during shutdown

[Samiullah Khawaja <skhawaja@google.com>]

On Wed, Aug 26, 2026 at 12:30:40PM +0000, Pranjal Shrivastava wrote:
>On Wed, Aug 26, 2026 at 04:05:51PM +0800, Baolu Lu wrote:
>> On 8/8/26 10:27, Samiullah Khawaja wrote:
>> > During normal shutdown the iommu translation is disabled. Since the root
>> > table is preserved during live update, it needs to be cleaned up and the
>> > context entries of the unpreserved devices and root entries for the
>> > unpreserved context tables need to be cleared.
>>
>> The key assumption here seems to be that, during a live-update kexec,
>> most devices do not go through the normal iommu release path. Otherwise,
>> their context entries should already be torn down in the
>> iommu_release_device path.
>>
>> Could you please confirm this assumption and add some short note in the
>> comments or commit message?
>>
>
>Yes, that's correct
>
>During the normal shutdown paths (i.e power-off, normal reboot, & kexec),
>the kernel only calls device_shutdown(). This path bypasses driver
>unbinding, as a result, devres_release_all() and iommu_release_device()
>are never called. Those devres teardown paths are only triggered when a
>driver is explicitly unloaded / device is unplugged.
>
>Since live-update piggybacks on the kexec/shutdown path the unpreserved
>devices never have their context entries naturally torn down by the core
>driver's devres model, necessitating this explicit cleanup.
>
>I think we can add a line in the commit msg for this because comments
>might create confusion if similar comments don't exist in other drivers
>performing Live Update. What do you think, Sami?

Agreed. I am going to add it both places.
>
>Thanks,
>Praan