drm/gpusvm: Use dma-map IOVA alloc, link, and sync API in GPU SVM

The dma-map IOVA alloc, link, and sync APIs perform significantly better
than dma-map / dma-unmap, as they avoid costly IOMMU synchronizations.
This difference is especially noticeable when mapping a 2MB region in
4KB pages.

Use the IOVA alloc, link, and sync APIs for GPU SVM, which create DMA
mappings between the CPU and GPU.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20260410205929.3914474-2-matthew.brost@intel.com

drivers/gpu/drm/drm_gpusvm.c

@@ -1139,11 +1139,17 @@ static void __drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
 		struct drm_gpusvm_pages_flags flags = {
 			.__flags = svm_pages->flags.__flags,
 		};
+		bool use_iova = dma_use_iova(&svm_pages->state);
+
+		if (use_iova)
+			dma_iova_destroy(dev, &svm_pages->state,
+					 svm_pages->state_offset,
+					 svm_pages->dma_addr[0].dir, 0);
 
 		for (i = 0, j = 0; i < npages; j++) {
 			struct drm_pagemap_addr *addr = &svm_pages->dma_addr[j];
 
-			if (addr->proto == DRM_INTERCONNECT_SYSTEM)
+			if (!use_iova && addr->proto == DRM_INTERCONNECT_SYSTEM)
 				dma_unmap_page(dev,
 					       addr->addr,
 					       PAGE_SIZE << addr->order,
@@ -1408,6 +1414,7 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 	struct drm_gpusvm_pages_flags flags;
 	enum dma_data_direction dma_dir = ctx->read_only ? DMA_TO_DEVICE :
 							   DMA_BIDIRECTIONAL;
+	struct dma_iova_state *state = &svm_pages->state;
 
 retry:
 	if (time_after(jiffies, timeout))
@@ -1446,6 +1453,9 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 	if (err)
 		goto err_free;
 
+	*state = (struct dma_iova_state){};
+	svm_pages->state_offset = 0;
+
 map_pages:
 	/*
 	 * Perform all dma mappings under the notifier lock to not
@@ -1539,13 +1549,33 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 				goto err_unmap;
 			}
 
-			addr = dma_map_page(gpusvm->drm->dev,
+			if (!i)
-					    page, 0,
+				dma_iova_try_alloc(gpusvm->drm->dev, state,
-					    PAGE_SIZE << order,
+						   npages * PAGE_SIZE >=
-					    dma_dir);
+						   HPAGE_PMD_SIZE ?
-			if (dma_mapping_error(gpusvm->drm->dev, addr)) {
+						   HPAGE_PMD_SIZE : 0,
-				err = -EFAULT;
+						   npages * PAGE_SIZE);
-				goto err_unmap;
+
+			if (dma_use_iova(state)) {
+				err = dma_iova_link(gpusvm->drm->dev, state,
+						    hmm_pfn_to_phys(pfns[i]),
+						    svm_pages->state_offset,
+						    PAGE_SIZE << order,
+						    dma_dir, 0);
+				if (err)
+					goto err_unmap;
+
+				addr = state->addr + svm_pages->state_offset;
+				svm_pages->state_offset += PAGE_SIZE << order;
+			} else {
+				addr = dma_map_page(gpusvm->drm->dev,
+						    page, 0,
+						    PAGE_SIZE << order,
+						    dma_dir);
+				if (dma_mapping_error(gpusvm->drm->dev, addr)) {
+					err = -EFAULT;
+					goto err_unmap;
+				}
 			}
 
 			svm_pages->dma_addr[j] = drm_pagemap_addr_encode
@@ -1557,6 +1587,13 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 		flags.has_dma_mapping = true;
 	}
 
+	if (dma_use_iova(state)) {
+		err = dma_iova_sync(gpusvm->drm->dev, state, 0,
+				    svm_pages->state_offset);
+		if (err)
+			goto err_unmap;
+	}
+
 	if (pagemap) {
 		flags.has_devmem_pages = true;
 		drm_pagemap_get(dpagemap);

include/drm/drm_gpusvm.h

@@ -6,6 +6,7 @@
 #ifndef __DRM_GPUSVM_H__
 #define __DRM_GPUSVM_H__
 
+#include <linux/dma-mapping.h>
 #include <linux/kref.h>
 #include <linux/interval_tree.h>
 #include <linux/mmu_notifier.h>
@@ -136,6 +137,8 @@ struct drm_gpusvm_pages_flags {
  * @dma_addr: Device address array
  * @dpagemap: The struct drm_pagemap of the device pages we're dma-mapping.
  *            Note this is assuming only one drm_pagemap per range is allowed.
+ * @state: DMA IOVA state for mapping.
+ * @state_offset: DMA IOVA offset for mapping.
  * @notifier_seq: Notifier sequence number of the range's pages
  * @flags: Flags for range
  * @flags.migrate_devmem: Flag indicating whether the range can be migrated to device memory
@@ -147,6 +150,8 @@ struct drm_gpusvm_pages_flags {
 struct drm_gpusvm_pages {
 	struct drm_pagemap_addr *dma_addr;
 	struct drm_pagemap *dpagemap;
+	struct dma_iova_state state;
+	unsigned long state_offset;
 	unsigned long notifier_seq;
 	struct drm_gpusvm_pages_flags flags;
 };