[PATCH RFC 9/9] iommu/vt-d: Introduce map_sg() for Intel IOMMUs

[Chuck Lever <chuck.lever@oracle.com>]

Attempt to reduce indirect call overhead when mapping a substantial
scatter-gather list.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 drivers/iommu/intel/iommu.c |   37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 013097b6d55f..deae39f1477a 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4952,6 +4952,42 @@ static int intel_iommu_map(struct iommu_domain *domain,
 				hpa >> VTD_PAGE_SHIFT, size, prot);
 }
 
+static int intel_iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
+			      struct scatterlist *sg, unsigned int nents,
+			      int prot, gfp_t gfp, size_t *mapped)
+{
+	unsigned int i = 0;
+	phys_addr_t start;
+	size_t len = 0;
+	int ret;
+
+	while (i <= nents) {
+		phys_addr_t s_phys = sg_phys(sg);
+
+		if (len && s_phys != start + len) {
+			ret = intel_iommu_map(domain, iova + *mapped, start,
+					      len, prot, gfp);
+			if (ret)
+				return ret;
+
+			*mapped += len;
+			len = 0;
+		}
+
+		if (len) {
+			len += sg->length;
+		} else {
+			len = sg->length;
+			start = s_phys;
+		}
+
+		if (++i < nents)
+			sg = sg_next(sg);
+	}
+
+	return 0;
+}
+
 static size_t intel_iommu_unmap(struct iommu_domain *domain,
 				unsigned long iova, size_t size,
 				struct iommu_iotlb_gather *gather)
@@ -5519,6 +5555,7 @@ const struct iommu_ops intel_iommu_ops = {
 	.aux_detach_dev		= intel_iommu_aux_detach_device,
 	.aux_get_pasid		= intel_iommu_aux_get_pasid,
 	.map			= intel_iommu_map,
+	.map_sg			= intel_iommu_map_sg,
 	.iotlb_sync_map		= intel_iommu_iotlb_sync_map,
 	.unmap			= intel_iommu_unmap,
 	.flush_iotlb_all        = intel_flush_iotlb_all,


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