RE: [PATCH 1/2] iommu/vt-d: Avoid unnecessary device TLB flush in map path

Tian, Kevin
2024-04-09T07:21:38Z

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Sunday, April 7, 2024 10:43 PM
>
> iommu_flush_iotlb_psi() is called in map and unmap paths. The caching
> mode check before device TLB invalidation will cause device TLB
> invalidation always issued if IOMMU is not running in the caching mode.
> This is inefficient and causes performance overhead.
>
> Make device TLB invalidation behavior consistent between batched mode
> unmapping and strict mode unmapping. Device TLB invalidation should only
> be requested in the unmap path if the IOMMU is not in caching mode.
>
> Fixes: bf92df30df90 ("intel-iommu: Only avoid flushing device IOTLB for
> domain ID 0 in caching mode")
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>

and given it only affects performance then not qualified for backporting?