drm/gpusvm: export drm_gpusvm_pages API

Export get/unmap/free pages API. We also need to tweak the SVM init to
allow skipping much of the unneeded parts.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250828142430.615826-15-matthew.auld@intel.com

Author: matt-auld

drivers/gpu/drm/drm_gpusvm.c

@@ -373,6 +373,12 @@ static const struct mmu_interval_notifier_ops drm_gpusvm_notifier_ops = {
  *
  * This function initializes the GPU SVM.
  *
+ * Note: If only using the simple drm_gpusvm_pages API (get/unmap/free),
+ * then only @gpusvm, @name, and @drm are expected. However, the same base
+ * @gpusvm can also be used with both modes together in which case the full
+ * setup is needed, where the core drm_gpusvm_pages API will simply never use
+ * the other fields.
+ *
  * Return: 0 on success, a negative error code on failure.
  */
 int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
@@ -383,8 +389,16 @@ int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
 		    const struct drm_gpusvm_ops *ops,
 		    const unsigned long *chunk_sizes, int num_chunks)
 {
-	if (!ops->invalidate || !num_chunks)
-		return -EINVAL;
+	if (mm) {
+		if (!ops->invalidate || !num_chunks)
+			return -EINVAL;
+		mmgrab(mm);
+	} else {
+		/* No full SVM mode, only core drm_gpusvm_pages API. */
+		if (ops || num_chunks || mm_range || notifier_size ||
+		    device_private_page_owner)
+			return -EINVAL;
+	}
 
 	gpusvm->name = name;
 	gpusvm->drm = drm;
@@ -397,7 +411,6 @@ int drm_gpusvm_init(struct drm_gpusvm *gpusvm,
 	gpusvm->chunk_sizes = chunk_sizes;
 	gpusvm->num_chunks = num_chunks;
 
-	mmgrab(mm);
 	gpusvm->root = RB_ROOT_CACHED;
 	INIT_LIST_HEAD(&gpusvm->notifier_list);
 
@@ -489,7 +502,8 @@ void drm_gpusvm_fini(struct drm_gpusvm *gpusvm)
 			drm_gpusvm_range_remove(gpusvm, range);
 	}
 
-	mmdrop(gpusvm->mm);
+	if (gpusvm->mm)
+		mmdrop(gpusvm->mm);
 	WARN_ON(!RB_EMPTY_ROOT(&gpusvm->root.rb_root));
 }
 EXPORT_SYMBOL_GPL(drm_gpusvm_fini);
@@ -1044,6 +1058,27 @@ static void __drm_gpusvm_free_pages(struct drm_gpusvm *gpusvm,
 	}
 }
 
+/**
+ * drm_gpusvm_free_pages() - Free dma-mapping associated with GPU SVM pages
+ * struct
+ * @gpusvm: Pointer to the GPU SVM structure
+ * @svm_pages: Pointer to the GPU SVM pages structure
+ * @npages: Number of mapped pages
+ *
+ * This function unmaps and frees the dma address array associated with a GPU
+ * SVM pages struct.
+ */
+void drm_gpusvm_free_pages(struct drm_gpusvm *gpusvm,
+			   struct drm_gpusvm_pages *svm_pages,
+			   unsigned long npages)
+{
+	drm_gpusvm_notifier_lock(gpusvm);
+	__drm_gpusvm_unmap_pages(gpusvm, svm_pages, npages);
+	__drm_gpusvm_free_pages(gpusvm, svm_pages);
+	drm_gpusvm_notifier_unlock(gpusvm);
+}
+EXPORT_SYMBOL_GPL(drm_gpusvm_free_pages);
+
 /**
  * drm_gpusvm_range_remove() - Remove GPU SVM range
  * @gpusvm: Pointer to the GPU SVM structure
@@ -1220,13 +1255,12 @@ static bool drm_gpusvm_pages_valid_unlocked(struct drm_gpusvm *gpusvm,
  *
  * Return: 0 on success, negative error code on failure.
  */
-static int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
-				struct drm_gpusvm_pages *svm_pages,
-				struct mm_struct *mm,
-				struct mmu_interval_notifier *notifier,
-				unsigned long pages_start,
-				unsigned long pages_end,
-				const struct drm_gpusvm_ctx *ctx)
+int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
+			 struct drm_gpusvm_pages *svm_pages,
+			 struct mm_struct *mm,
+			 struct mmu_interval_notifier *notifier,
+			 unsigned long pages_start, unsigned long pages_end,
+			 const struct drm_gpusvm_ctx *ctx)
 {
 	struct hmm_range hmm_range = {
 		.default_flags = HMM_PFN_REQ_FAULT | (ctx->read_only ? 0 :
@@ -1415,6 +1449,7 @@ static int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 		goto retry;
 	return err;
 }
+EXPORT_SYMBOL_GPL(drm_gpusvm_get_pages);
 
 /**
  * drm_gpusvm_range_get_pages() - Get pages for a GPU SVM range
@@ -1451,10 +1486,10 @@ EXPORT_SYMBOL_GPL(drm_gpusvm_range_get_pages);
  * Must be called in the invalidate() callback of the corresponding notifier for
  * IOMMU security model.
  */
-static void drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
-				   struct drm_gpusvm_pages *svm_pages,
-				   unsigned long npages,
-				   const struct drm_gpusvm_ctx *ctx)
+void drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
+			    struct drm_gpusvm_pages *svm_pages,
+			    unsigned long npages,
+			    const struct drm_gpusvm_ctx *ctx)
 {
 	if (ctx->in_notifier)
 		lockdep_assert_held_write(&gpusvm->notifier_lock);
@@ -1466,6 +1501,7 @@ static void drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
 	if (!ctx->in_notifier)
 		drm_gpusvm_notifier_unlock(gpusvm);
 }
+EXPORT_SYMBOL_GPL(drm_gpusvm_unmap_pages);
 
 /**
  * drm_gpusvm_range_unmap_pages() - Unmap pages associated with a GPU SVM range

include/drm/drm_gpusvm.h

@@ -307,6 +307,22 @@ drm_gpusvm_range_find(struct drm_gpusvm_notifier *notifier, unsigned long start,
 void drm_gpusvm_range_set_unmapped(struct drm_gpusvm_range *range,
 				   const struct mmu_notifier_range *mmu_range);
 
+int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
+			 struct drm_gpusvm_pages *svm_pages,
+			 struct mm_struct *mm,
+			 struct mmu_interval_notifier *notifier,
+			 unsigned long pages_start, unsigned long pages_end,
+			 const struct drm_gpusvm_ctx *ctx);
+
+void drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
+			    struct drm_gpusvm_pages *svm_pages,
+			    unsigned long npages,
+			    const struct drm_gpusvm_ctx *ctx);
+
+void drm_gpusvm_free_pages(struct drm_gpusvm *gpusvm,
+			   struct drm_gpusvm_pages *svm_pages,
+			   unsigned long npages);
+
 #ifdef CONFIG_LOCKDEP
 /**
  * drm_gpusvm_driver_set_lock() - Set the lock protecting accesses to GPU SVM