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

[Jacob Pan]

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: <stable@xxxxxxxxxxxxxxx>
Tested-by: Sanjay Kumar <sanjay.k.kumar@xxxxxxxxx>
Signed-off-by: Sanjay Kumar <sanjay.k.kumar@xxxxxxxxx>
Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
 drivers/iommu/intel/iommu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index b4878c7ac008..705a1c66691a 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4352,7 +4352,13 @@ 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,
+	 * There is no need to track page and sync iotlb. Domain-selective or
+	 * PASID-selective validation are used in the flush queue.
+	 */
+	if (!gather->queued)
+		iommu_iotlb_gather_add_page(domain, gather, iova, size);
 
 	return size;
 }
-- 
2.25.1