Re: [PATCH RFC 15/19] iommu/arm-smmu-v3: Add set_dirty_tracking_range() support

Robin Murphy
2022-04-29T11:19:22Z

On 2022-04-29 12:05, Joao Martins wrote:
> On 4/29/22 09:28, Tian, Kevin wrote:
>>> From: Joao Martins <joao.m.martins@oracle.com>
>>> Sent: Friday, April 29, 2022 5:09 AM
>>>
>>> Similar to .read_and_clear_dirty() use the page table
>>> walker helper functions and set DBM|RDONLY bit, thus
>>> switching the IOPTE to writeable-clean.
>>
>> this should not be one-off if the operation needs to be
>> applied to IOPTE. Say a map request comes right after
>> set_dirty_tracking() is called. If it's agreed to remove
>> the range op then smmu driver should record the tracking
>> status internally and then apply the modifier to all the new
>> mappings automatically before dirty tracking is disabled.
>> Otherwise the same logic needs to be kept in iommufd to
>> call set_dirty_tracking_range() explicitly for every new
>> iopt_area created within the tracking window.
>
> Gah, I totally missed that by mistake. New mappings aren't
> carrying over the "DBM is set". This needs a new io-pgtable
> quirk added post dirty-tracking toggling.
>
> I can adjust, but I am at odds on including this in a future
> iteration given that I can't really test any of this stuff.
> Might drop the driver until I have hardware/emulation I can
> use (or maybe others can take over this). It was included
> for revising the iommu core ops and whether iommufd was
> affected by it.
>
> I'll delete the range op, and let smmu v3 driver walk its
> own IO pgtables.

TBH I'd be inclined to just enable DBM unconditionally in
arm_smmu_domain_finalise() if the SMMU supports it. Trying to toggle it
dynamically (especially on a live domain) seems more trouble that it's
worth.

Robin.