iommu/vt-d: Avoid superfluous IOTLB tracking in lazy mode

Intel IOMMU driver implements IOTLB flush queue with domain selective
or PASID selective invalidations. In this case there's no need to track
IOVA page range and sync IOTLBs, which may cause significant performance
hit.

This patch adds a check to avoid IOVA gather page and IOTLB sync for
the lazy path.

The performance difference on Sapphire Rapids 100Gb NIC is improved by
the following (as measured by iperf send):

w/o this fix~48 Gbits/s. with this fix ~54 Gbits/s

Cc: <[email protected]>
Fixes: 2a2b8ea ("iommu: Handle freelists when using deferred flushing in iommu drivers")
Reviewed-by: Robin Murphy <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Tested-by: Sanjay Kumar <[email protected]>
Signed-off-by: Sanjay Kumar <[email protected]>
Signed-off-by: Jacob Pan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Lu Baolu <[email protected]>
Signed-off-by: Joerg Roedel <[email protected]>

Author: Jacob Pan

drivers/iommu/intel/iommu.c

@@ -4348,7 +4348,12 @@ static size_t intel_iommu_unmap(struct iommu_domain *domain,
 	if (dmar_domain->max_addr == iova + size)
 		dmar_domain->max_addr = iova;
 
-	iommu_iotlb_gather_add_page(domain, gather, iova, size);
+	/*
+	 * We do not use page-selective IOTLB invalidation in flush queue,
+	 * so there is no need to track page and sync iotlb.
+	 */
+	if (!iommu_iotlb_gather_queued(gather))
+		iommu_iotlb_gather_add_page(domain, gather, iova, size);
 
 	return size;
 }