Re: [PATCH v6 15/17] iommu/arm-smmu-v3: Add INV_TYPE_ATS_BROKEN for quarantined masters

[sashiko-bot@kernel.org]

> Clearing STE.EATS makes the SMMU reject ATS requests from any quarantined
> master, but does not stop the driver from issuing ATC invalidations for it.
> Those commands would continue to time out.
> 
> Introduce INV_TYPE_ATS_BROKEN, which a subsequent change will assign to the
> master's ATS invalidation entries. Treat it as an ATS type during iteration
> and ordering, but skip it when issuing commands.
> 
> The subsequent quarantine path changes inv->type in place via WRITE_ONCE()
> while readers hold the invalidation array's read lock. Since a u8 load is
> already atomic, arm_smmu_inv_type() uses READ_ONCE() to annotate the race
> for KCSAN. Whole-struct copies in merge and purge cannot use READ_ONCE(),
> so annotate those copies with data_race().
> 
> A stale read at worst issues one more ATC_INV, which times out and causes
> the master to be quarantined again.
> 
> Treat ATS, ATS_FULL, and ATS_BROKEN as one comparator class. This preserves
> the sort position and matching identity when an entry is changed in place.
> 
> No functional change yet; the new type is never set anywhere.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Assisted-by: LLM
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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