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* [PATCH 1/2] drm/gpusvm: Add a DMA-mapping accounting callback
@ 2026-11-04 21:52 Matthew Brost
  2026-11-04 21:52 ` [PATCH 2/2] drm/xe: Add debugfs stats for DMA-mapped pages per order Matthew Brost
                   ` (8 more replies)
  0 siblings, 9 replies; 16+ messages in thread
From: Matthew Brost @ 2026-11-04 21:52 UTC (permalink / raw)
  To: intel-xe, dri-devel; +Cc: Thomas Hellström, Niranjana Vishwanathapura

From: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Drivers that use the GPU SVM core to DMA-map system memory for GPU
access may want to keep track of how many pages they have mapped, for
example to expose statistics or to detect leaks. Doing this accounting
in the driver around drm_gpusvm_get_pages() / drm_gpusvm_unmap_pages()
is error prone: the number, order and kind of the dma_addr[] entries can
change between map and unmap (migration, partial unmaps, the iova vs
non-iova paths), which makes symmetric accounting hard to get right.

Add an optional @dma_map_account callback to struct drm_gpusvm_ops and
invoke it once per &drm_pagemap_addr entry at the exact points where the
entry is DMA-mapped (sign == +1) in drm_gpusvm_get_pages() and unmapped
(sign == -1) in __drm_gpusvm_unmap_pages(). Since the map error path and
every unmap/free path funnel through __drm_gpusvm_unmap_pages() for the
entries that were actually mapped, the accounting is symmetric by
construction. The callback receives the full &drm_pagemap_addr so the
driver can use the order and the proto field to distinguish system
memory mappings from device interconnect mappings.

The callback must also be usable by the core drm_gpusvm_pages-only API
(mm == NULL), as used e.g. for userptr-style mappings. Relax
drm_gpusvm_init() to allow such users to pass a restricted @ops that
only implements the page-level hooks; the full-SVM hooks (@invalidate)
and the chunk configuration must still be unset in that mode.

Assisted-by: LLM
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
---
 drivers/gpu/drm/drm_gpusvm.c | 40 ++++++++++++++++++++++++++++--------
 include/drm/drm_gpusvm.h     | 19 +++++++++++++++++
 2 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
index 03dbe304e4b8..5ef9d7233491 100644
--- a/drivers/gpu/drm/drm_gpusvm.c
+++ b/drivers/gpu/drm/drm_gpusvm.c
@@ -503,8 +503,15 @@ int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
 			return -EINVAL;
 		mmgrab(mm);
 	} else {
-		/* No full SVM mode, only core drm_gpusvm_pages API. */
-		if (ops || num_chunks || mm_range || notifier_size)
+		/*
+		 * No full SVM mode, only core drm_gpusvm_pages API. A
+		 * restricted @ops that only implements the page-level hooks
+		 * (e.g. @dma_map_account) is allowed; the full-SVM hooks must
+		 * not be set.
+		 */
+		if (num_chunks || mm_range || notifier_size)
+			return -EINVAL;
+		if (ops && ops->invalidate)
 			return -EINVAL;
 	}
 
@@ -1240,9 +1247,12 @@ static void __drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
 		struct drm_gpusvm_pages_flags flags = {
 			.__flags = svm_pages->flags.__flags,
 		};
+		bool contiguous;
 		const struct drm_pagemap_addr *addrs =
-			drm_gpusvm_pages_first_dma(svm_pages, NULL);
+			drm_gpusvm_pages_first_dma(svm_pages, &contiguous);
 		bool use_iova = dma_use_iova(&svm_pages->state);
+		bool needs_account = gpusvm->ops &&
+			gpusvm->ops->dma_map_account;
 
 		/*
 		 * IOVA is reserved for the whole range but only the linked
@@ -1260,14 +1270,18 @@ static void __drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
 
 		/*
 		 * With IOVA and no device page the unlink above tore every
-		 * entry down, and that is also when the range may be folded
-		 * to one entry, which must not be walked per entry. dpagemap
-		 * is set before the first device_map(), so it is also right
-		 * on the error path, where the flags are not published yet.
+		 * entry down, but the per-entry walk is still needed when the
+		 * driver accounts the mappings. A folded (inline) mapping has
+		 * a single entry describing the whole range, so it must be
+		 * re-read for every iteration instead of indexed by @j.
+		 * dpagemap is set before the first device_map(), so it is also
+		 * right on the error path, where the flags are not published
+		 * yet.
 		 */
 		for (i = 0, j = 0;
-		     (!use_iova || dpagemap) && i < npages; j++) {
-			const struct drm_pagemap_addr *addr = &addrs[j];
+		     (!use_iova || dpagemap || needs_account) && i < npages; j++) {
+			const struct drm_pagemap_addr *addr =
+				contiguous ? &addrs[0] : &addrs[j];
 
 			if (addr->proto == DRM_INTERCONNECT_SYSTEM) {
 				/*
@@ -1283,6 +1297,10 @@ static void __drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
 			} else if (dpagemap && dpagemap->ops->device_unmap)
 				dpagemap->ops->device_unmap(dpagemap,
 							    dev, addr);
+
+			if (needs_account)
+				gpusvm->ops->dma_map_account(gpusvm, addr, -1);
+
 			i += 1 << addr->order;
 		}
 
@@ -1705,6 +1723,10 @@ static int drm_gpusvm_dma_map_pages(struct drm_gpusvm *gpusvm,
 				(addr, DRM_INTERCONNECT_SYSTEM, order,
 				 dma_dir);
 		}
+		if (gpusvm->ops && gpusvm->ops->dma_map_account)
+			gpusvm->ops->dma_map_account(gpusvm,
+						     &svm_pages->dma_addr[j],
+						     1);
 		i += 1 << order;
 		num_dma_mapped = i;
 		flags.has_dma_mapping = true;
diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
index 4d31c6bba745..637c19f7169f 100644
--- a/include/drm/drm_gpusvm.h
+++ b/include/drm/drm_gpusvm.h
@@ -75,6 +75,25 @@ struct drm_gpusvm_ops {
 	void (*invalidate)(struct drm_gpusvm *gpusvm,
 			   struct drm_gpusvm_notifier *notifier,
 			   const struct mmu_notifier_range *mmu_range);
+
+	/**
+	 * @dma_map_account: Account a DMA-mapping change (optional)
+	 * @gpusvm: Pointer to the GPU SVM
+	 * @addr: The address descriptor of the chunk being (un)mapped
+	 * @sign: +1 when @addr has just been DMA-mapped, -1 when it is being
+	 *        unmapped
+	 *
+	 * Called once per &drm_pagemap_addr entry, when the entry is
+	 * DMA-mapped by drm_gpusvm_get_pages() (@sign == +1) and when it is
+	 * unmapped (@sign == -1), so the driver can keep symmetric accounting
+	 * of the pages it has mapped for GPU access. The @addr->proto field
+	 * can be used to distinguish system-memory mappings from device
+	 * interconnect mappings. May be provided in both full SVM mode and the
+	 * core drm_gpusvm_pages-only mode.
+	 */
+	void (*dma_map_account)(struct drm_gpusvm *gpusvm,
+				const struct drm_pagemap_addr *addr,
+				int sign);
 };
 
 /**
-- 
2.34.1


^ permalink raw reply related	[flat|nested] 16+ messages in thread

end of thread, other threads:[~2026-11-05 22:57 UTC | newest]

Thread overview: 16+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-11-04 21:52 [PATCH 1/2] drm/gpusvm: Add a DMA-mapping accounting callback Matthew Brost
2026-11-04 21:52 ` [PATCH 2/2] drm/xe: Add debugfs stats for DMA-mapped pages per order Matthew Brost
2026-11-04 22:15   ` sashiko-bot
2026-11-04 22:20     ` Matthew Brost
2026-11-05  1:16   ` Niranjana Vishwanathapura
2026-11-05  2:49     ` Matthew Brost
2026-11-05  3:21       ` Niranjana Vishwanathapura
2026-11-04 21:59 ` ✗ CI.checkpatch: warning for series starting with [1/2] drm/gpusvm: Add a DMA-mapping accounting callback Patchwork
2026-11-04 22:01 ` ✓ CI.KUnit: success " Patchwork
2026-11-04 22:37 ` ✓ Xe.CI.BAT: " Patchwork
2026-11-05  0:49 ` [PATCH 1/2] " Niranjana Vishwanathapura
2026-11-05  2:49   ` Matthew Brost
2026-11-05  5:49 ` ✗ CI.checkpatch: warning for series starting with [1/2] drm/gpusvm: Add a DMA-mapping accounting callback (rev2) Patchwork
2026-11-05  5:51 ` ✓ CI.KUnit: success " Patchwork
2026-11-05  6:28 ` ✓ Xe.CI.BAT: " Patchwork
2026-11-05 22:57 ` ✗ Xe.CI.FULL: failure " Patchwork

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