[PATCH v3] 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>
Fixes: 2a2b8eaa5b25 ("iommu: Handle freelists when using deferred flushing in iommu drivers")
Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
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>
---
v3: reword comments, add reviewed by tag. (Kevin)
v2: use helper function iommu_iotlb_gather_queued() instead of open
coding
---
 drivers/iommu/intel/iommu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 59df7e42fd53..2ee270e4d484 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4346,7 +4346,12 @@ 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;
 }
-- 
2.25.1