Nouveau - Aug 2019 - [PATCH 01/10] mm: turn migrate_vma upside down

Hi Jérôme, Ben and Jason,

below is a series against the hmm tree which starts revamping the
migrate_vma functionality.  The prime idea is to export three slightly
lower level functions and thus avoid the need for migrate_vma_ops
callbacks.

Diffstat:

    7 files changed, 282 insertions(+), 614 deletions(-)

A git tree is also available at:

    git://git.infradead.org/users/hch/misc.git migrate_vma-cleanup.3

Gitweb:

   
http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/migrate_vma-cleanup.3


Changes since v2:
 - don't unmap pages when returning 0 from nouveau_dmem_migrate_to_ram
 - minor style fixes
 - add a new patch to remove CONFIG_MIGRATE_VMA_HELPER

Changes since v1:
 - fix a few whitespace issues
 - drop the patch to remove MIGRATE_PFN_WRITE for now
 - various spelling fixes
 - clear cpages and npages in migrate_vma_setup
 - fix the nouveau_dmem_fault_copy_one return value
 - minor improvements to some nouveau internal calling conventions

There isn't any good reason to pass callbacks to migrate_vma.  Instead
we can just export the three steps done by this function to drivers and
let them sequence the operation without callbacks.  This removes a lot
of boilerplate code as-is, and will allow the drivers to drastically
improve code flow and error handling further on.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 Documentation/vm/hmm.rst               |  55 +-----
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 122 +++++++------
 include/linux/migrate.h                | 118 ++----------
 mm/migrate.c                           | 244 +++++++++++--------------
 4 files changed, 195 insertions(+), 344 deletions(-)

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index e63c11f7e0e0..4f81c77059e3 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -339,58 +339,9 @@ Migration to and from device memory
 ================================== 
 Because the CPU cannot access device memory, migration must use the device DMA
-engine to perform copy from and to device memory. For this we need a new
-migration helper::
-
- int migrate_vma(const struct migrate_vma_ops *ops,
-                 struct vm_area_struct *vma,
-                 unsigned long mentries,
-                 unsigned long start,
-                 unsigned long end,
-                 unsigned long *src,
-                 unsigned long *dst,
-                 void *private);
-
-Unlike other migration functions it works on a range of virtual address, there
-are two reasons for that. First, device DMA copy has a high setup overhead cost
-and thus batching multiple pages is needed as otherwise the migration overhead
-makes the whole exercise pointless. The second reason is because the
-migration might be for a range of addresses the device is actively accessing.
-
-The migrate_vma_ops struct defines two callbacks. First one (alloc_and_copy())
-controls destination memory allocation and copy operation. Second one is there
-to allow the device driver to perform cleanup operations after migration::
-
- struct migrate_vma_ops {
-     void (*alloc_and_copy)(struct vm_area_struct *vma,
-                            const unsigned long *src,
-                            unsigned long *dst,
-                            unsigned long start,
-                            unsigned long end,
-                            void *private);
-     void (*finalize_and_map)(struct vm_area_struct *vma,
-                              const unsigned long *src,
-                              const unsigned long *dst,
-                              unsigned long start,
-                              unsigned long end,
-                              void *private);
- };
-
-It is important to stress that these migration helpers allow for holes in the
-virtual address range. Some pages in the range might not be migrated for all
-the usual reasons (page is pinned, page is locked, ...). This helper does not
-fail but just skips over those pages.
-
-The alloc_and_copy() might decide to not migrate all pages in the
-range (for reasons under the callback control). For those, the callback just
-has to leave the corresponding dst entry empty.
-
-Finally, the migration of the struct page might fail (for file backed page) for
-various reasons (failure to freeze reference, or update page cache, ...). If
-that happens, then the finalize_and_map() can catch any pages that were not
-migrated. Note those pages were still copied to a new page and thus we wasted
-bandwidth but this is considered as a rare event and a price that we are
-willing to pay to keep all the code simpler.
+engine to perform copy from and to device memory. For this we need a new to
+use migrate_vma_setup(), migrate_vma_pages(), and migrate_vma_finalize()
+helpers.
 
 
 Memory cgroup (memcg) and rss accounting
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 345c63cb752a..38416798abd4 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -131,9 +131,8 @@ nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct
*vma,
 				  unsigned long *dst_pfns,
 				  unsigned long start,
 				  unsigned long end,
-				  void *private)
+				  struct nouveau_dmem_fault *fault)
 {
-	struct nouveau_dmem_fault *fault = private;
 	struct nouveau_drm *drm = fault->drm;
 	struct device *dev = drm->dev->dev;
 	unsigned long addr, i, npages = 0;
@@ -230,14 +229,9 @@ nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct
*vma,
 	}
 }
 
-void nouveau_dmem_fault_finalize_and_map(struct vm_area_struct *vma,
-					 const unsigned long *src_pfns,
-					 const unsigned long *dst_pfns,
-					 unsigned long start,
-					 unsigned long end,
-					 void *private)
+static void
+nouveau_dmem_fault_finalize_and_map(struct nouveau_dmem_fault *fault)
 {
-	struct nouveau_dmem_fault *fault = private;
 	struct nouveau_drm *drm = fault->drm;
 
 	if (fault->fence) {
@@ -257,29 +251,35 @@ void nouveau_dmem_fault_finalize_and_map(struct
vm_area_struct *vma,
 	kfree(fault->dma);
 }
 
-static const struct migrate_vma_ops nouveau_dmem_fault_migrate_ops = {
-	.alloc_and_copy		= nouveau_dmem_fault_alloc_and_copy,
-	.finalize_and_map	= nouveau_dmem_fault_finalize_and_map,
-};
-
 static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
 {
 	struct nouveau_dmem *dmem = page_to_dmem(vmf->page);
 	unsigned long src[1] = {0}, dst[1] = {0};
+	struct migrate_vma args = {
+		.vma		= vmf->vma,
+		.start		= vmf->address,
+		.end		= vmf->address + PAGE_SIZE,
+		.src		= src,
+		.dst		= dst,
+	};
 	struct nouveau_dmem_fault fault = { .drm = dmem->drm };
-	int ret;
 
 	/*
 	 * FIXME what we really want is to find some heuristic to migrate more
 	 * than just one page on CPU fault. When such fault happens it is very
 	 * likely that more surrounding page will CPU fault too.
 	 */
-	ret = migrate_vma(&nouveau_dmem_fault_migrate_ops, vmf->vma,
-			vmf->address, vmf->address + PAGE_SIZE,
-			src, dst, &fault);
-	if (ret)
+	if (migrate_vma_setup(&args) < 0)
 		return VM_FAULT_SIGBUS;
+	if (!args.cpages)
+		return 0;
+
+	nouveau_dmem_fault_alloc_and_copy(args.vma, src, dst, args.start,
+			args.end, &fault);
+	migrate_vma_pages(&args);
+	nouveau_dmem_fault_finalize_and_map(&fault);
 
+	migrate_vma_finalize(&args);
 	if (dst[0] == MIGRATE_PFN_ERROR)
 		return VM_FAULT_SIGBUS;
 
@@ -648,9 +648,8 @@ nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct
*vma,
 				    unsigned long *dst_pfns,
 				    unsigned long start,
 				    unsigned long end,
-				    void *private)
+				    struct nouveau_migrate *migrate)
 {
-	struct nouveau_migrate *migrate = private;
 	struct nouveau_drm *drm = migrate->drm;
 	struct device *dev = drm->dev->dev;
 	unsigned long addr, i, npages = 0;
@@ -747,14 +746,9 @@ nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct
*vma,
 	}
 }
 
-void nouveau_dmem_migrate_finalize_and_map(struct vm_area_struct *vma,
-					   const unsigned long *src_pfns,
-					   const unsigned long *dst_pfns,
-					   unsigned long start,
-					   unsigned long end,
-					   void *private)
+static void
+nouveau_dmem_migrate_finalize_and_map(struct nouveau_migrate *migrate)
 {
-	struct nouveau_migrate *migrate = private;
 	struct nouveau_drm *drm = migrate->drm;
 
 	if (migrate->fence) {
@@ -779,10 +773,15 @@ void nouveau_dmem_migrate_finalize_and_map(struct
vm_area_struct *vma,
 	 */
 }
 
-static const struct migrate_vma_ops nouveau_dmem_migrate_ops = {
-	.alloc_and_copy		= nouveau_dmem_migrate_alloc_and_copy,
-	.finalize_and_map	= nouveau_dmem_migrate_finalize_and_map,
-};
+static void nouveau_dmem_migrate_chunk(struct migrate_vma *args,
+		struct nouveau_migrate *migrate)
+{
+	nouveau_dmem_migrate_alloc_and_copy(args->vma, args->src, args->dst,
+			args->start, args->end, migrate);
+	migrate_vma_pages(args);
+	nouveau_dmem_migrate_finalize_and_map(migrate);
+	migrate_vma_finalize(args);
+}
 
 int
 nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
@@ -790,40 +789,45 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 			 unsigned long start,
 			 unsigned long end)
 {
-	unsigned long *src_pfns, *dst_pfns, npages;
-	struct nouveau_migrate migrate = {0};
-	unsigned long i, c, max;
-	int ret = 0;
-
-	npages = (end - start) >> PAGE_SHIFT;
-	max = min(SG_MAX_SINGLE_ALLOC, npages);
-	src_pfns = kzalloc(sizeof(long) * max, GFP_KERNEL);
-	if (src_pfns == NULL)
-		return -ENOMEM;
-	dst_pfns = kzalloc(sizeof(long) * max, GFP_KERNEL);
-	if (dst_pfns == NULL) {
-		kfree(src_pfns);
-		return -ENOMEM;
-	}
+	unsigned long npages = (end - start) >> PAGE_SHIFT;
+	unsigned long max = min(SG_MAX_SINGLE_ALLOC, npages);
+	struct migrate_vma args = {
+		.vma		= vma,
+		.start		= start,
+	};
+	struct nouveau_migrate migrate = {
+		.drm		= drm,
+		.vma		= vma,
+		.npages		= npages,
+	};
+	unsigned long c, i;
+	int ret = -ENOMEM;
+
+	args.src = kzalloc(sizeof(long) * max, GFP_KERNEL);
+	if (!args.src)
+		goto out;
+	args.dst = kzalloc(sizeof(long) * max, GFP_KERNEL);
+	if (!args.dst)
+		goto out_free_src;
 
-	migrate.drm = drm;
-	migrate.vma = vma;
-	migrate.npages = npages;
 	for (i = 0; i < npages; i += c) {
-		unsigned long next;
-
 		c = min(SG_MAX_SINGLE_ALLOC, npages);
-		next = start + (c << PAGE_SHIFT);
-		ret = migrate_vma(&nouveau_dmem_migrate_ops, vma, start,
-				  next, src_pfns, dst_pfns, &migrate);
+		args.end = start + (c << PAGE_SHIFT);
+		ret = migrate_vma_setup(&args);
 		if (ret)
-			goto out;
-		start = next;
+			goto out_free_dst;
+
+		if (args.cpages)
+			nouveau_dmem_migrate_chunk(&args, &migrate);
+		args.start = args.end;
 	}
 
+	ret = 0;
+out_free_dst:
+	kfree(args.dst);
+out_free_src:
+	kfree(args.src);
 out:
-	kfree(dst_pfns);
-	kfree(src_pfns);
 	return ret;
 }
 
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 7f04754c7f2b..18156d379ebf 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -182,107 +182,27 @@ static inline unsigned long migrate_pfn(unsigned long
pfn)
 	return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID;
 }
 
-/*
- * struct migrate_vma_ops - migrate operation callback
- *
- * @alloc_and_copy: alloc destination memory and copy source memory to it
- * @finalize_and_map: allow caller to map the successfully migrated pages
- *
- *
- * The alloc_and_copy() callback happens once all source pages have been
locked,
- * unmapped and checked (checked whether pinned or not). All pages that can be
- * migrated will have an entry in the src array set with the pfn value of the
- * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set (other
- * flags might be set but should be ignored by the callback).
- *
- * The alloc_and_copy() callback can then allocate destination memory and copy
- * source memory to it for all those entries (ie with MIGRATE_PFN_VALID and
- * MIGRATE_PFN_MIGRATE flag set). Once these are allocated and copied, the
- * callback must update each corresponding entry in the dst array with the pfn
- * value of the destination page and with the MIGRATE_PFN_VALID and
- * MIGRATE_PFN_LOCKED flags set (destination pages must have their struct pages
- * locked, via lock_page()).
- *
- * At this point the alloc_and_copy() callback is done and returns.
- *
- * Note that the callback does not have to migrate all the pages that are
- * marked with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration
- * from device memory to system memory (ie the MIGRATE_PFN_DEVICE flag is also
- * set in the src array entry). If the device driver cannot migrate a device
- * page back to system memory, then it must set the corresponding dst array
- * entry to MIGRATE_PFN_ERROR. This will trigger a SIGBUS if CPU tries to
- * access any of the virtual addresses originally backed by this page. Because
- * a SIGBUS is such a severe result for the userspace process, the device
- * driver should avoid setting MIGRATE_PFN_ERROR unless it is really in an
- * unrecoverable state.
- *
- * For empty entry inside CPU page table (pte_none() or pmd_none() is true) we
- * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
- * allowing device driver to allocate device memory for those unback virtual
- * address. For this the device driver simply have to allocate device memory
- * and properly set the destination entry like for regular migration. Note that
- * this can still fails and thus inside the device driver must check if the
- * migration was successful for those entry inside the finalize_and_map()
- * callback just like for regular migration.
- *
- * THE alloc_and_copy() CALLBACK MUST NOT CHANGE ANY OF THE SRC ARRAY ENTRIES
- * OR BAD THINGS WILL HAPPEN !
- *
- *
- * The finalize_and_map() callback happens after struct page migration from
- * source to destination (destination struct pages are the struct pages for the
- * memory allocated by the alloc_and_copy() callback).  Migration can fail, and
- * thus the finalize_and_map() allows the driver to inspect which pages were
- * successfully migrated, and which were not. Successfully migrated pages will
- * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
- *
- * It is safe to update device page table from within the finalize_and_map()
- * callback because both destination and source page are still locked, and the
- * mmap_sem is held in read mode (hence no one can unmap the range being
- * migrated).
- *
- * Once callback is done cleaning up things and updating its page table (if it
- * chose to do so, this is not an obligation) then it returns. At this point,
- * the HMM core will finish up the final steps, and the migration is complete.
- *
- * THE finalize_and_map() CALLBACK MUST NOT CHANGE ANY OF THE SRC OR DST ARRAY
- * ENTRIES OR BAD THINGS WILL HAPPEN !
- */
-struct migrate_vma_ops {
-	void (*alloc_and_copy)(struct vm_area_struct *vma,
-			       const unsigned long *src,
-			       unsigned long *dst,
-			       unsigned long start,
-			       unsigned long end,
-			       void *private);
-	void (*finalize_and_map)(struct vm_area_struct *vma,
-				 const unsigned long *src,
-				 const unsigned long *dst,
-				 unsigned long start,
-				 unsigned long end,
-				 void *private);
+struct migrate_vma {
+	struct vm_area_struct	*vma;
+	/*
+	 * Both src and dst array must be big enough for
+	 * (end - start) >> PAGE_SHIFT entries.
+	 *
+	 * The src array must not be modified by the caller after
+	 * migrate_vma_setup(), and must not change the dst array after
+	 * migrate_vma_pages() returns.
+	 */
+	unsigned long		*dst;
+	unsigned long		*src;
+	unsigned long		cpages;
+	unsigned long		npages;
+	unsigned long		start;
+	unsigned long		end;
 };
 
-#if defined(CONFIG_MIGRATE_VMA_HELPER)
-int migrate_vma(const struct migrate_vma_ops *ops,
-		struct vm_area_struct *vma,
-		unsigned long start,
-		unsigned long end,
-		unsigned long *src,
-		unsigned long *dst,
-		void *private);
-#else
-static inline int migrate_vma(const struct migrate_vma_ops *ops,
-			      struct vm_area_struct *vma,
-			      unsigned long start,
-			      unsigned long end,
-			      unsigned long *src,
-			      unsigned long *dst,
-			      void *private)
-{
-	return -EINVAL;
-}
-#endif /* IS_ENABLED(CONFIG_MIGRATE_VMA_HELPER) */
+int migrate_vma_setup(struct migrate_vma *args);
+void migrate_vma_pages(struct migrate_vma *migrate);
+void migrate_vma_finalize(struct migrate_vma *migrate);
 
 #endif /* CONFIG_MIGRATION */
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 8992741f10aa..e2565374d330 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2118,16 +2118,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct
*mm,
 #endif /* CONFIG_NUMA */
 
 #if defined(CONFIG_MIGRATE_VMA_HELPER)
-struct migrate_vma {
-	struct vm_area_struct	*vma;
-	unsigned long		*dst;
-	unsigned long		*src;
-	unsigned long		cpages;
-	unsigned long		npages;
-	unsigned long		start;
-	unsigned long		end;
-};
-
 static int migrate_vma_collect_hole(unsigned long start,
 				    unsigned long end,
 				    struct mm_walk *walk)
@@ -2578,6 +2568,110 @@ static void migrate_vma_unmap(struct migrate_vma
*migrate)
 	}
 }
 
+/**
+ * migrate_vma_setup() - prepare to migrate a range of memory
+ * @args: contains the vma, start, and and pfns arrays for the migration
+ *
+ * Returns: negative errno on failures, 0 when 0 or more pages were migrated
+ * without an error.
+ *
+ * Prepare to migrate a range of memory virtual address range by collecting all
+ * the pages backing each virtual address in the range, saving them inside the
+ * src array.  Then lock those pages and unmap them. Once the pages are locked
+ * and unmapped, check whether each page is pinned or not.  Pages that
aren't
+ * pinned have the MIGRATE_PFN_MIGRATE flag set (by this function) in the
+ * corresponding src array entry.  Then restores any pages that are pinned, by
+ * remapping and unlocking those pages.
+ *
+ * The caller should then allocate destination memory and copy source memory to
+ * it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
+ * flag set).  Once these are allocated and copied, the caller must update each
+ * corresponding entry in the dst array with the pfn value of the destination
+ * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_LOCKED flags set
+ * (destination pages must have their struct pages locked, via lock_page()).
+ *
+ * Note that the caller does not have to migrate all the pages that are marked
+ * with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from
+ * device memory to system memory.  If the caller cannot migrate a device page
+ * back to system memory, then it must return VM_FAULT_SIGBUS, which has severe
+ * consequences for the userspace process, so it must be avoided if at all
+ * possible.
+ *
+ * For empty entries inside CPU page table (pte_none() or pmd_none() is true)
we
+ * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
+ * allowing the caller to allocate device memory for those unback virtual
+ * address.  For this the caller simply has to allocate device memory and
+ * properly set the destination entry like for regular migration.  Note that
+ * this can still fails and thus inside the device driver must check if the
+ * migration was successful for those entries after calling migrate_vma_pages()
+ * just like for regular migration.
+ *
+ * After that, the callers must call migrate_vma_pages() to go over each entry
+ * in the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
+ * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
+ * then migrate_vma_pages() to migrate struct page information from the source
+ * struct page to the destination struct page.  If it fails to migrate the
+ * struct page information, then it clears the MIGRATE_PFN_MIGRATE flag in the
+ * src array.
+ *
+ * At this point all successfully migrated pages have an entry in the src
+ * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
+ * array entry with MIGRATE_PFN_VALID flag set.
+ *
+ * Once migrate_vma_pages() returns the caller may inspect which pages were
+ * successfully migrated, and which were not.  Successfully migrated pages will
+ * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
+ *
+ * It is safe to update device page table from within the finalize_and_map()
+ * callback because both destination and source page are still locked, and the
+ * mmap_sem is held in read mode (hence no one can unmap the range being
+ * migrated).
+ *
+ * Once the caller is done cleaning up things and updating its page table (if
it
+ * chose to do so, this is not an obligation) it finally calls
+ * migrate_vma_finalize() to update the CPU page table to point to new pages
+ * for successfully migrated pages or otherwise restore the CPU page table to
+ * point to the original source pages.
+ */
+int migrate_vma_setup(struct migrate_vma *args)
+{
+	long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
+
+	args->start &= PAGE_MASK;
+	args->end &= PAGE_MASK;
+	if (!args->vma || is_vm_hugetlb_page(args->vma) ||
+	    (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
+		return -EINVAL;
+	if (nr_pages <= 0)
+		return -EINVAL;
+	if (args->start < args->vma->vm_start ||
+	    args->start >= args->vma->vm_end)
+		return -EINVAL;
+	if (args->end <= args->vma->vm_start || args->end >
args->vma->vm_end)
+		return -EINVAL;
+	if (!args->src || !args->dst)
+		return -EINVAL;
+
+	memset(args->src, 0, sizeof(*args->src) * nr_pages);
+	args->cpages = 0;
+	args->npages = 0;
+
+	migrate_vma_collect(args);
+	if (args->cpages)
+		migrate_vma_prepare(args);
+	if (args->cpages)
+		migrate_vma_unmap(args);
+
+	/*
+	 * At this point pages are locked and unmapped, and thus they have
+	 * stable content and can safely be copied to destination memory that
+	 * is allocated by the drivers.
+	 */
+	return 0;
+
+}
+EXPORT_SYMBOL(migrate_vma_setup);
+
 static void migrate_vma_insert_page(struct migrate_vma *migrate,
 				    unsigned long addr,
 				    struct page *page,
@@ -2709,7 +2803,7 @@ static void migrate_vma_insert_page(struct migrate_vma
*migrate,
 	*src &= ~MIGRATE_PFN_MIGRATE;
 }
 
-/*
+/**
  * migrate_vma_pages() - migrate meta-data from src page to dst page
  * @migrate: migrate struct containing all migration information
  *
@@ -2717,7 +2811,7 @@ static void migrate_vma_insert_page(struct migrate_vma
*migrate,
  * struct page. This effectively finishes the migration from source page to the
  * destination page.
  */
-static void migrate_vma_pages(struct migrate_vma *migrate)
+void migrate_vma_pages(struct migrate_vma *migrate)
 {
 	const unsigned long npages = migrate->npages;
 	const unsigned long start = migrate->start;
@@ -2791,8 +2885,9 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
 	if (notified)
 		mmu_notifier_invalidate_range_only_end(&range);
 }
+EXPORT_SYMBOL(migrate_vma_pages);
 
-/*
+/**
  * migrate_vma_finalize() - restore CPU page table entry
  * @migrate: migrate struct containing all migration information
  *
@@ -2803,7 +2898,7 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
  * This also unlocks the pages and puts them back on the lru, or drops the
extra
  * refcount, for device pages.
  */
-static void migrate_vma_finalize(struct migrate_vma *migrate)
+void migrate_vma_finalize(struct migrate_vma *migrate)
 {
 	const unsigned long npages = migrate->npages;
 	unsigned long i;
@@ -2846,124 +2941,5 @@ static void migrate_vma_finalize(struct migrate_vma
*migrate)
 		}
 	}
 }
-
-/*
- * migrate_vma() - migrate a range of memory inside vma
- *
- * @ops: migration callback for allocating destination memory and copying
- * @vma: virtual memory area containing the range to be migrated
- * @start: start address of the range to migrate (inclusive)
- * @end: end address of the range to migrate (exclusive)
- * @src: array of hmm_pfn_t containing source pfns
- * @dst: array of hmm_pfn_t containing destination pfns
- * @private: pointer passed back to each of the callback
- * Returns: 0 on success, error code otherwise
- *
- * This function tries to migrate a range of memory virtual address range,
using
- * callbacks to allocate and copy memory from source to destination. First it
- * collects all the pages backing each virtual address in the range, saving
this
- * inside the src array. Then it locks those pages and unmaps them. Once the
pages
- * are locked and unmapped, it checks whether each page is pinned or not. Pages
- * that aren't pinned have the MIGRATE_PFN_MIGRATE flag set (by this
function)
- * in the corresponding src array entry. It then restores any pages that are
- * pinned, by remapping and unlocking those pages.
- *
- * At this point it calls the alloc_and_copy() callback. For documentation on
- * what is expected from that callback, see struct migrate_vma_ops comments in
- * include/linux/migrate.h
- *
- * After the alloc_and_copy() callback, this function goes over each entry in
- * the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
- * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
- * then the function tries to migrate struct page information from the source
- * struct page to the destination struct page. If it fails to migrate the
struct
- * page information, then it clears the MIGRATE_PFN_MIGRATE flag in the src
- * array.
- *
- * At this point all successfully migrated pages have an entry in the src
- * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
- * array entry with MIGRATE_PFN_VALID flag set.
- *
- * It then calls the finalize_and_map() callback. See comments for "struct
- * migrate_vma_ops", in include/linux/migrate.h for details about
- * finalize_and_map() behavior.
- *
- * After the finalize_and_map() callback, for successfully migrated pages, this
- * function updates the CPU page table to point to new pages, otherwise it
- * restores the CPU page table to point to the original source pages.
- *
- * Function returns 0 after the above steps, even if no pages were migrated
- * (The function only returns an error if any of the arguments are invalid.)
- *
- * Both src and dst array must be big enough for (end - start) >>
PAGE_SHIFT
- * unsigned long entries.
- */
-int migrate_vma(const struct migrate_vma_ops *ops,
-		struct vm_area_struct *vma,
-		unsigned long start,
-		unsigned long end,
-		unsigned long *src,
-		unsigned long *dst,
-		void *private)
-{
-	struct migrate_vma migrate;
-
-	/* Sanity check the arguments */
-	start &= PAGE_MASK;
-	end &= PAGE_MASK;
-	if (!vma || is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
-			vma_is_dax(vma))
-		return -EINVAL;
-	if (start < vma->vm_start || start >= vma->vm_end)
-		return -EINVAL;
-	if (end <= vma->vm_start || end > vma->vm_end)
-		return -EINVAL;
-	if (!ops || !src || !dst || start >= end)
-		return -EINVAL;
-
-	memset(src, 0, sizeof(*src) * ((end - start) >> PAGE_SHIFT));
-	migrate.src = src;
-	migrate.dst = dst;
-	migrate.start = start;
-	migrate.npages = 0;
-	migrate.cpages = 0;
-	migrate.end = end;
-	migrate.vma = vma;
-
-	/* Collect, and try to unmap source pages */
-	migrate_vma_collect(&migrate);
-	if (!migrate.cpages)
-		return 0;
-
-	/* Lock and isolate page */
-	migrate_vma_prepare(&migrate);
-	if (!migrate.cpages)
-		return 0;
-
-	/* Unmap pages */
-	migrate_vma_unmap(&migrate);
-	if (!migrate.cpages)
-		return 0;
-
-	/*
-	 * At this point pages are locked and unmapped, and thus they have
-	 * stable content and can safely be copied to destination memory that
-	 * is allocated by the callback.
-	 *
-	 * Note that migration can fail in migrate_vma_struct_page() for each
-	 * individual page.
-	 */
-	ops->alloc_and_copy(vma, src, dst, start, end, private);
-
-	/* This does the real migration of struct page */
-	migrate_vma_pages(&migrate);
-
-	ops->finalize_and_map(vma, src, dst, start, end, private);
-
-	/* Unlock and remap pages */
-	migrate_vma_finalize(&migrate);
-
-	return 0;
-}
-EXPORT_SYMBOL(migrate_vma);
+EXPORT_SYMBOL(migrate_vma_finalize);
 #endif /* defined(MIGRATE_VMA_HELPER) */
-- 
2.20.1

When we start a new batch of dma_map operations we need to reset dma_nr,
as we start filling a newly allocated array.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 38416798abd4..e696157f771e 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -682,6 +682,7 @@ nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct
*vma,
 	migrate->dma = kmalloc(sizeof(*migrate->dma) * npages, GFP_KERNEL);
 	if (!migrate->dma)
 		goto error;
+	migrate->dma_nr = 0;
 
 	/* Copy things over */
 	copy = drm->dmem->migrate.copy_func;
-- 
2.20.1

Factor out the repeated device memory address calculation into
a helper.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 42 +++++++++++---------------
 1 file changed, 17 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index e696157f771e..d469bc334438 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -102,6 +102,14 @@ struct nouveau_migrate {
 	unsigned long dma_nr;
 };
 
+static unsigned long nouveau_dmem_page_addr(struct page *page)
+{
+	struct nouveau_dmem_chunk *chunk = page->zone_device_data;
+	unsigned long idx = page_to_pfn(page) - chunk->pfn_first;
+
+	return (idx << PAGE_SHIFT) + chunk->bo->bo.offset;
+}
+
 static void nouveau_dmem_page_free(struct page *page)
 {
 	struct nouveau_dmem_chunk *chunk = page->zone_device_data;
@@ -169,9 +177,7 @@ nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct
*vma,
 	/* Copy things over */
 	copy = drm->dmem->migrate.copy_func;
 	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, i++) {
-		struct nouveau_dmem_chunk *chunk;
 		struct page *spage, *dpage;
-		u64 src_addr, dst_addr;
 
 		dpage = migrate_pfn_to_page(dst_pfns[i]);
 		if (!dpage || dst_pfns[i] == MIGRATE_PFN_ERROR)
@@ -194,14 +200,10 @@ nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct
*vma,
 			continue;
 		}
 
-		dst_addr = fault->dma[fault->npages++];
-
-		chunk = spage->zone_device_data;
-		src_addr = page_to_pfn(spage) - chunk->pfn_first;
-		src_addr = (src_addr << PAGE_SHIFT) + chunk->bo->bo.offset;
-
-		ret = copy(drm, 1, NOUVEAU_APER_HOST, dst_addr,
-				   NOUVEAU_APER_VRAM, src_addr);
+		ret = copy(drm, 1, NOUVEAU_APER_HOST,
+				fault->dma[fault->npages++],
+				NOUVEAU_APER_VRAM,
+				nouveau_dmem_page_addr(spage));
 		if (ret) {
 			dst_pfns[i] = MIGRATE_PFN_ERROR;
 			__free_page(dpage);
@@ -687,18 +689,12 @@ nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct
*vma,
 	/* Copy things over */
 	copy = drm->dmem->migrate.copy_func;
 	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, i++) {
-		struct nouveau_dmem_chunk *chunk;
 		struct page *spage, *dpage;
-		u64 src_addr, dst_addr;
 
 		dpage = migrate_pfn_to_page(dst_pfns[i]);
 		if (!dpage || dst_pfns[i] == MIGRATE_PFN_ERROR)
 			continue;
 
-		chunk = dpage->zone_device_data;
-		dst_addr = page_to_pfn(dpage) - chunk->pfn_first;
-		dst_addr = (dst_addr << PAGE_SHIFT) + chunk->bo->bo.offset;
-
 		spage = migrate_pfn_to_page(src_pfns[i]);
 		if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE)) {
 			nouveau_dmem_page_free_locked(drm, dpage);
@@ -716,10 +712,10 @@ nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct
*vma,
 			continue;
 		}
 
-		src_addr = migrate->dma[migrate->dma_nr++];
-
-		ret = copy(drm, 1, NOUVEAU_APER_VRAM, dst_addr,
-				   NOUVEAU_APER_HOST, src_addr);
+		ret = copy(drm, 1, NOUVEAU_APER_VRAM,
+				nouveau_dmem_page_addr(dpage),
+				NOUVEAU_APER_HOST,
+				migrate->dma[migrate->dma_nr++]);
 		if (ret) {
 			nouveau_dmem_page_free_locked(drm, dpage);
 			dst_pfns[i] = 0;
@@ -846,7 +842,6 @@ nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
 
 	npages = (range->end - range->start) >> PAGE_SHIFT;
 	for (i = 0; i < npages; ++i) {
-		struct nouveau_dmem_chunk *chunk;
 		struct page *page;
 		uint64_t addr;
 
@@ -864,10 +859,7 @@ nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
 			continue;
 		}
 
-		chunk = page->zone_device_data;
-		addr = page_to_pfn(page) - chunk->pfn_first;
-		addr = (addr + chunk->bo->bo.mem.start) << PAGE_SHIFT;
-
+		addr = nouveau_dmem_page_addr(page);
 		range->pfns[i] &= ((1UL << range->pfn_shift) - 1);
 		range->pfns[i] |= (addr >> PAGE_SHIFT) << range->pfn_shift;
 	}
-- 
2.20.1

Factor out the end of fencing logic from the two migration routines.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 33 ++++++++++++--------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index d469bc334438..21052a4aaf69 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -133,6 +133,19 @@ static void nouveau_dmem_page_free(struct page *page)
 	spin_unlock(&chunk->lock);
 }
 
+static void nouveau_dmem_fence_done(struct nouveau_fence **fence)
+{
+	if (fence) {
+		nouveau_fence_wait(*fence, true, false);
+		nouveau_fence_unref(fence);
+	} else {
+		/*
+		 * FIXME wait for channel to be IDLE before calling finalizing
+		 * the hmem object.
+		 */
+	}
+}
+
 static void
 nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct *vma,
 				  const unsigned long *src_pfns,
@@ -236,15 +249,7 @@ nouveau_dmem_fault_finalize_and_map(struct
nouveau_dmem_fault *fault)
 {
 	struct nouveau_drm *drm = fault->drm;
 
-	if (fault->fence) {
-		nouveau_fence_wait(fault->fence, true, false);
-		nouveau_fence_unref(&fault->fence);
-	} else {
-		/*
-		 * FIXME wait for channel to be IDLE before calling finalizing
-		 * the hmem object below (nouveau_migrate_hmem_fini()).
-		 */
-	}
+	nouveau_dmem_fence_done(&fault->fence);
 
 	while (fault->npages--) {
 		dma_unmap_page(drm->dev->dev, fault->dma[fault->npages],
@@ -748,15 +753,7 @@ nouveau_dmem_migrate_finalize_and_map(struct
nouveau_migrate *migrate)
 {
 	struct nouveau_drm *drm = migrate->drm;
 
-	if (migrate->fence) {
-		nouveau_fence_wait(migrate->fence, true, false);
-		nouveau_fence_unref(&migrate->fence);
-	} else {
-		/*
-		 * FIXME wait for channel to be IDLE before finalizing
-		 * the hmem object below (nouveau_migrate_hmem_fini()) ?
-		 */
-	}
+	nouveau_dmem_fence_done(&migrate->fence);
 
 	while (migrate->dma_nr--) {
 		dma_unmap_page(drm->dev->dev, migrate->dma[migrate->dma_nr],
-- 
2.20.1

nouveau_dmem_migrate_vma and nouveau_dmem_convert_pfn are only called
when CONFIG_DRM_NOUVEAU_SVM is enabled, so there is no need to provide
!CONFIG_DRM_NOUVEAU_SVM stubs for them.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.h | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.h
b/drivers/gpu/drm/nouveau/nouveau_dmem.h
index 9d97d756fb7d..92394be5d649 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.h
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.h
@@ -45,16 +45,5 @@ static inline void nouveau_dmem_init(struct nouveau_drm *drm)
{}
 static inline void nouveau_dmem_fini(struct nouveau_drm *drm) {}
 static inline void nouveau_dmem_suspend(struct nouveau_drm *drm) {}
 static inline void nouveau_dmem_resume(struct nouveau_drm *drm) {}
-
-static inline int nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
-					   struct vm_area_struct *vma,
-					   unsigned long start,
-					   unsigned long end)
-{
-	return 0;
-}
-
-static inline void nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
-					    struct hmm_range *range) {}
 #endif /* IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM) */
 #endif
-- 
2.20.1

Factor the main copy page to ram routine out into a helper that acts on
a single page and which doesn't require the nouveau_dmem_fault
structure for argument passing.  Also remove the loop over multiple
pages as we only handle one at the moment, although the structure of
the main worker function makes it relatively easy to add multi page
support back if needed in the future.  But at least for now this avoid
the needed to dynamically allocate memory for the dma addresses in
what is essentially the page fault path.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 161 ++++++-------------------
 1 file changed, 40 insertions(+), 121 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 21052a4aaf69..7dded864022c 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -86,13 +86,6 @@ static inline struct nouveau_dmem *page_to_dmem(struct page
*page)
 	return container_of(page->pgmap, struct nouveau_dmem, pagemap);
 }
 
-struct nouveau_dmem_fault {
-	struct nouveau_drm *drm;
-	struct nouveau_fence *fence;
-	dma_addr_t *dma;
-	unsigned long npages;
-};
-
 struct nouveau_migrate {
 	struct vm_area_struct *vma;
 	struct nouveau_drm *drm;
@@ -146,130 +139,55 @@ static void nouveau_dmem_fence_done(struct nouveau_fence
**fence)
 	}
 }
 
-static void
-nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct *vma,
-				  const unsigned long *src_pfns,
-				  unsigned long *dst_pfns,
-				  unsigned long start,
-				  unsigned long end,
-				  struct nouveau_dmem_fault *fault)
+static vm_fault_t nouveau_dmem_fault_copy_one(struct nouveau_drm *drm,
+		struct vm_fault *vmf, struct migrate_vma *args,
+		dma_addr_t *dma_addr)
 {
-	struct nouveau_drm *drm = fault->drm;
 	struct device *dev = drm->dev->dev;
-	unsigned long addr, i, npages = 0;
-	nouveau_migrate_copy_t copy;
-	int ret;
-
-
-	/* First allocate new memory */
-	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, i++) {
-		struct page *dpage, *spage;
-
-		dst_pfns[i] = 0;
-		spage = migrate_pfn_to_page(src_pfns[i]);
-		if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE))
-			continue;
-
-		dpage = alloc_page_vma(GFP_HIGHUSER, vma, addr);
-		if (!dpage) {
-			dst_pfns[i] = MIGRATE_PFN_ERROR;
-			continue;
-		}
-		lock_page(dpage);
-
-		dst_pfns[i] = migrate_pfn(page_to_pfn(dpage)) |
-			      MIGRATE_PFN_LOCKED;
-		npages++;
-	}
-
-	/* Allocate storage for DMA addresses, so we can unmap later. */
-	fault->dma = kmalloc(sizeof(*fault->dma) * npages, GFP_KERNEL);
-	if (!fault->dma)
-		goto error;
-
-	/* Copy things over */
-	copy = drm->dmem->migrate.copy_func;
-	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, i++) {
-		struct page *spage, *dpage;
-
-		dpage = migrate_pfn_to_page(dst_pfns[i]);
-		if (!dpage || dst_pfns[i] == MIGRATE_PFN_ERROR)
-			continue;
-
-		spage = migrate_pfn_to_page(src_pfns[i]);
-		if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE)) {
-			dst_pfns[i] = MIGRATE_PFN_ERROR;
-			__free_page(dpage);
-			continue;
-		}
+	struct page *dpage, *spage;
 
-		fault->dma[fault->npages] -			dma_map_page_attrs(dev, dpage, 0,
PAGE_SIZE,
-					   PCI_DMA_BIDIRECTIONAL,
-					   DMA_ATTR_SKIP_CPU_SYNC);
-		if (dma_mapping_error(dev, fault->dma[fault->npages])) {
-			dst_pfns[i] = MIGRATE_PFN_ERROR;
-			__free_page(dpage);
-			continue;
-		}
-
-		ret = copy(drm, 1, NOUVEAU_APER_HOST,
-				fault->dma[fault->npages++],
-				NOUVEAU_APER_VRAM,
-				nouveau_dmem_page_addr(spage));
-		if (ret) {
-			dst_pfns[i] = MIGRATE_PFN_ERROR;
-			__free_page(dpage);
-			continue;
-		}
-	}
-
-	nouveau_fence_new(drm->dmem->migrate.chan, false, &fault->fence);
-
-	return;
-
-error:
-	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, ++i) {
-		struct page *page;
-
-		if (!dst_pfns[i] || dst_pfns[i] == MIGRATE_PFN_ERROR)
-			continue;
+	spage = migrate_pfn_to_page(args->src[0]);
+	if (!spage || !(args->src[0] & MIGRATE_PFN_MIGRATE))
+		return 0;
 
-		page = migrate_pfn_to_page(dst_pfns[i]);
-		dst_pfns[i] = MIGRATE_PFN_ERROR;
-		if (page == NULL)
-			continue;
+	dpage = alloc_page_vma(GFP_HIGHUSER, vmf->vma, vmf->address);
+	if (!dpage)
+		return VM_FAULT_SIGBUS;
+	lock_page(dpage);
 
-		__free_page(page);
-	}
-}
+	*dma_addr = dma_map_page(dev, dpage, 0, PAGE_SIZE, DMA_BIDIRECTIONAL);
+	if (dma_mapping_error(dev, *dma_addr))
+		goto error_free_page;
 
-static void
-nouveau_dmem_fault_finalize_and_map(struct nouveau_dmem_fault *fault)
-{
-	struct nouveau_drm *drm = fault->drm;
+	if (drm->dmem->migrate.copy_func(drm, 1, NOUVEAU_APER_HOST, *dma_addr,
+			NOUVEAU_APER_VRAM, nouveau_dmem_page_addr(spage)))
+		goto error_dma_unmap;
 
-	nouveau_dmem_fence_done(&fault->fence);
+	args->dst[0] = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
+	return 0;
 
-	while (fault->npages--) {
-		dma_unmap_page(drm->dev->dev, fault->dma[fault->npages],
-			       PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
-	}
-	kfree(fault->dma);
+error_dma_unmap:
+	dma_unmap_page(dev, *dma_addr, PAGE_SIZE, DMA_BIDIRECTIONAL);
+error_free_page:
+	__free_page(dpage);
+	return VM_FAULT_SIGBUS;
 }
 
 static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
 {
 	struct nouveau_dmem *dmem = page_to_dmem(vmf->page);
-	unsigned long src[1] = {0}, dst[1] = {0};
+	struct nouveau_drm *drm = dmem->drm;
+	struct nouveau_fence *fence;
+	unsigned long src = 0, dst = 0;
+	dma_addr_t dma_addr = 0;
+	vm_fault_t ret;
 	struct migrate_vma args = {
 		.vma		= vmf->vma,
 		.start		= vmf->address,
 		.end		= vmf->address + PAGE_SIZE,
-		.src		= src,
-		.dst		= dst,
+		.src		= &src,
+		.dst		= &dst,
 	};
-	struct nouveau_dmem_fault fault = { .drm = dmem->drm };
 
 	/*
 	 * FIXME what we really want is to find some heuristic to migrate more
@@ -281,16 +199,17 @@ static vm_fault_t nouveau_dmem_migrate_to_ram(struct
vm_fault *vmf)
 	if (!args.cpages)
 		return 0;
 
-	nouveau_dmem_fault_alloc_and_copy(args.vma, src, dst, args.start,
-			args.end, &fault);
-	migrate_vma_pages(&args);
-	nouveau_dmem_fault_finalize_and_map(&fault);
+	ret = nouveau_dmem_fault_copy_one(drm, vmf, &args, &dma_addr);
+	if (ret || dst == 0)
+		goto done;
 
+	nouveau_fence_new(dmem->migrate.chan, false, &fence);
+	migrate_vma_pages(&args);
+	nouveau_dmem_fence_done(&fence);
+	dma_unmap_page(drm->dev->dev, dma_addr, PAGE_SIZE, DMA_BIDIRECTIONAL);
+done:
 	migrate_vma_finalize(&args);
-	if (dst[0] == MIGRATE_PFN_ERROR)
-		return VM_FAULT_SIGBUS;
-
-	return 0;
+	return ret;
 }
 
 static const struct dev_pagemap_ops nouveau_dmem_pagemap_ops = {
-- 
2.20.1

Factor the main copy page to vram routine out into a helper that acts
on a single page and which doesn't require the nouveau_dmem_migrate
structure for argument passing.  As an added benefit the new version
only allocates the dma address array once and reuses it for each
subsequent chunk of work.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 184 ++++++++-----------------
 1 file changed, 55 insertions(+), 129 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 7dded864022c..d96b987b9982 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -44,8 +44,6 @@
 #define DMEM_CHUNK_SIZE (2UL << 20)
 #define DMEM_CHUNK_NPAGES (DMEM_CHUNK_SIZE >> PAGE_SHIFT)
 
-struct nouveau_migrate;
-
 enum nouveau_aper {
 	NOUVEAU_APER_VIRT,
 	NOUVEAU_APER_VRAM,
@@ -86,15 +84,6 @@ static inline struct nouveau_dmem *page_to_dmem(struct page
*page)
 	return container_of(page->pgmap, struct nouveau_dmem, pagemap);
 }
 
-struct nouveau_migrate {
-	struct vm_area_struct *vma;
-	struct nouveau_drm *drm;
-	struct nouveau_fence *fence;
-	unsigned long npages;
-	dma_addr_t *dma;
-	unsigned long dma_nr;
-};
-
 static unsigned long nouveau_dmem_page_addr(struct page *page)
 {
 	struct nouveau_dmem_chunk *chunk = page->zone_device_data;
@@ -568,131 +557,66 @@ nouveau_dmem_init(struct nouveau_drm *drm)
 	drm->dmem = NULL;
 }
 
-static void
-nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct *vma,
-				    const unsigned long *src_pfns,
-				    unsigned long *dst_pfns,
-				    unsigned long start,
-				    unsigned long end,
-				    struct nouveau_migrate *migrate)
+static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
+		unsigned long src, dma_addr_t *dma_addr)
 {
-	struct nouveau_drm *drm = migrate->drm;
 	struct device *dev = drm->dev->dev;
-	unsigned long addr, i, npages = 0;
-	nouveau_migrate_copy_t copy;
-	int ret;
-
-	/* First allocate new memory */
-	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, i++) {
-		struct page *dpage, *spage;
-
-		dst_pfns[i] = 0;
-		spage = migrate_pfn_to_page(src_pfns[i]);
-		if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE))
-			continue;
-
-		dpage = nouveau_dmem_page_alloc_locked(drm);
-		if (!dpage)
-			continue;
-
-		dst_pfns[i] = migrate_pfn(page_to_pfn(dpage)) |
-			      MIGRATE_PFN_LOCKED |
-			      MIGRATE_PFN_DEVICE;
-		npages++;
-	}
-
-	if (!npages)
-		return;
-
-	/* Allocate storage for DMA addresses, so we can unmap later. */
-	migrate->dma = kmalloc(sizeof(*migrate->dma) * npages, GFP_KERNEL);
-	if (!migrate->dma)
-		goto error;
-	migrate->dma_nr = 0;
-
-	/* Copy things over */
-	copy = drm->dmem->migrate.copy_func;
-	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, i++) {
-		struct page *spage, *dpage;
-
-		dpage = migrate_pfn_to_page(dst_pfns[i]);
-		if (!dpage || dst_pfns[i] == MIGRATE_PFN_ERROR)
-			continue;
-
-		spage = migrate_pfn_to_page(src_pfns[i]);
-		if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE)) {
-			nouveau_dmem_page_free_locked(drm, dpage);
-			dst_pfns[i] = 0;
-			continue;
-		}
-
-		migrate->dma[migrate->dma_nr] -			dma_map_page_attrs(dev, spage, 0,
PAGE_SIZE,
-					   PCI_DMA_BIDIRECTIONAL,
-					   DMA_ATTR_SKIP_CPU_SYNC);
-		if (dma_mapping_error(dev, migrate->dma[migrate->dma_nr])) {
-			nouveau_dmem_page_free_locked(drm, dpage);
-			dst_pfns[i] = 0;
-			continue;
-		}
-
-		ret = copy(drm, 1, NOUVEAU_APER_VRAM,
-				nouveau_dmem_page_addr(dpage),
-				NOUVEAU_APER_HOST,
-				migrate->dma[migrate->dma_nr++]);
-		if (ret) {
-			nouveau_dmem_page_free_locked(drm, dpage);
-			dst_pfns[i] = 0;
-			continue;
-		}
-	}
+	struct page *dpage, *spage;
 
-	nouveau_fence_new(drm->dmem->migrate.chan, false,
&migrate->fence);
+	spage = migrate_pfn_to_page(src);
+	if (!spage || !(src & MIGRATE_PFN_MIGRATE))
+		goto out;
 
-	return;
+	dpage = nouveau_dmem_page_alloc_locked(drm);
+	if (!dpage)
+		return 0;
 
-error:
-	for (addr = start, i = 0; addr < end; addr += PAGE_SIZE, ++i) {
-		struct page *page;
+	*dma_addr = dma_map_page(dev, spage, 0, PAGE_SIZE, DMA_BIDIRECTIONAL);
+	if (dma_mapping_error(dev, *dma_addr))
+		goto out_free_page;
 
-		if (!dst_pfns[i] || dst_pfns[i] == MIGRATE_PFN_ERROR)
-			continue;
+	if (drm->dmem->migrate.copy_func(drm, 1, NOUVEAU_APER_VRAM,
+			nouveau_dmem_page_addr(dpage), NOUVEAU_APER_HOST,
+			*dma_addr))
+		goto out_dma_unmap;
 
-		page = migrate_pfn_to_page(dst_pfns[i]);
-		dst_pfns[i] = MIGRATE_PFN_ERROR;
-		if (page == NULL)
-			continue;
+	return migrate_pfn(page_to_pfn(dpage)) |
+		MIGRATE_PFN_LOCKED | MIGRATE_PFN_DEVICE;
 
-		__free_page(page);
-	}
+out_dma_unmap:
+	dma_unmap_page(dev, *dma_addr, PAGE_SIZE, DMA_BIDIRECTIONAL);
+out_free_page:
+	nouveau_dmem_page_free_locked(drm, dpage);
+out:
+	return 0;
 }
 
-static void
-nouveau_dmem_migrate_finalize_and_map(struct nouveau_migrate *migrate)
+static void nouveau_dmem_migrate_chunk(struct nouveau_drm *drm,
+		struct migrate_vma *args, dma_addr_t *dma_addrs)
 {
-	struct nouveau_drm *drm = migrate->drm;
+	struct nouveau_fence *fence;
+	unsigned long addr = args->start, nr_dma = 0, i;
+
+	for (i = 0; addr < args->end; i++) {
+		args->dst[i] = nouveau_dmem_migrate_copy_one(drm, args->src[i],
+				dma_addrs + nr_dma);
+		if (args->dst[i])
+			nr_dma++;
+		addr += PAGE_SIZE;
+	}
 
-	nouveau_dmem_fence_done(&migrate->fence);
+	nouveau_fence_new(drm->dmem->migrate.chan, false, &fence);
+	migrate_vma_pages(args);
+	nouveau_dmem_fence_done(&fence);
 
-	while (migrate->dma_nr--) {
-		dma_unmap_page(drm->dev->dev, migrate->dma[migrate->dma_nr],
-			       PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
+	while (nr_dma--) {
+		dma_unmap_page(drm->dev->dev, dma_addrs[nr_dma], PAGE_SIZE,
+				DMA_BIDIRECTIONAL);
 	}
-	kfree(migrate->dma);
-
 	/*
-	 * FIXME optimization: update GPU page table to point to newly
-	 * migrated memory.
+	 * FIXME optimization: update GPU page table to point to newly migrated
+	 * memory.
 	 */
-}
-
-static void nouveau_dmem_migrate_chunk(struct migrate_vma *args,
-		struct nouveau_migrate *migrate)
-{
-	nouveau_dmem_migrate_alloc_and_copy(args->vma, args->src, args->dst,
-			args->start, args->end, migrate);
-	migrate_vma_pages(args);
-	nouveau_dmem_migrate_finalize_and_map(migrate);
 	migrate_vma_finalize(args);
 }
 
@@ -704,38 +628,40 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 {
 	unsigned long npages = (end - start) >> PAGE_SHIFT;
 	unsigned long max = min(SG_MAX_SINGLE_ALLOC, npages);
+	dma_addr_t *dma_addrs;
 	struct migrate_vma args = {
 		.vma		= vma,
 		.start		= start,
 	};
-	struct nouveau_migrate migrate = {
-		.drm		= drm,
-		.vma		= vma,
-		.npages		= npages,
-	};
 	unsigned long c, i;
 	int ret = -ENOMEM;
 
-	args.src = kzalloc(sizeof(long) * max, GFP_KERNEL);
+	args.src = kcalloc(max, sizeof(args.src), GFP_KERNEL);
 	if (!args.src)
 		goto out;
-	args.dst = kzalloc(sizeof(long) * max, GFP_KERNEL);
+	args.dst = kcalloc(max, sizeof(args.dst), GFP_KERNEL);
 	if (!args.dst)
 		goto out_free_src;
 
+	dma_addrs = kmalloc_array(max, sizeof(*dma_addrs), GFP_KERNEL);
+	if (!dma_addrs)
+		goto out_free_dst;
+
 	for (i = 0; i < npages; i += c) {
 		c = min(SG_MAX_SINGLE_ALLOC, npages);
 		args.end = start + (c << PAGE_SHIFT);
 		ret = migrate_vma_setup(&args);
 		if (ret)
-			goto out_free_dst;
+			goto out_free_dma;
 
 		if (args.cpages)
-			nouveau_dmem_migrate_chunk(&args, &migrate);
+			nouveau_dmem_migrate_chunk(drm, &args, dma_addrs);
 		args.start = args.end;
 	}
 
 	ret = 0;
+out_free_dma:
+	kfree(dma_addrs);
 out_free_dst:
 	kfree(args.dst);
 out_free_src:
-- 
2.20.1

Now that we can rely errors in the normal control flow there is no
need for this flag, remove it.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 include/linux/migrate.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 18156d379ebf..1e67dcfd318f 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -167,7 +167,6 @@ static inline int migrate_misplaced_transhuge_page(struct
mm_struct *mm,
 #define MIGRATE_PFN_LOCKED	(1UL << 2)
 #define MIGRATE_PFN_WRITE	(1UL << 3)
 #define MIGRATE_PFN_DEVICE	(1UL << 4)
-#define MIGRATE_PFN_ERROR	(1UL << 5)
 #define MIGRATE_PFN_SHIFT	6
 
 static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
-- 
2.20.1

No one ever checks this flag, and we could easily get that information
from the page if needed.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 3 +--
 include/linux/migrate.h                | 1 -
 mm/migrate.c                           | 4 ++--
 3 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index d96b987b9982..fa1439941596 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -580,8 +580,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct
nouveau_drm *drm,
 			*dma_addr))
 		goto out_dma_unmap;
 
-	return migrate_pfn(page_to_pfn(dpage)) |
-		MIGRATE_PFN_LOCKED | MIGRATE_PFN_DEVICE;
+	return migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
 
 out_dma_unmap:
 	dma_unmap_page(dev, *dma_addr, PAGE_SIZE, DMA_BIDIRECTIONAL);
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 1e67dcfd318f..72120061b7d4 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -166,7 +166,6 @@ static inline int migrate_misplaced_transhuge_page(struct
mm_struct *mm,
 #define MIGRATE_PFN_MIGRATE	(1UL << 1)
 #define MIGRATE_PFN_LOCKED	(1UL << 2)
 #define MIGRATE_PFN_WRITE	(1UL << 3)
-#define MIGRATE_PFN_DEVICE	(1UL << 4)
 #define MIGRATE_PFN_SHIFT	6
 
 static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
diff --git a/mm/migrate.c b/mm/migrate.c
index e2565374d330..33e063c28c1b 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2237,8 +2237,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 				goto next;
 
 			page = device_private_entry_to_page(entry);
-			mpfn = migrate_pfn(page_to_pfn(page))|
-				MIGRATE_PFN_DEVICE | MIGRATE_PFN_MIGRATE;
+			mpfn = migrate_pfn(page_to_pfn(page)) |
+					MIGRATE_PFN_MIGRATE;
 			if (is_write_device_private_entry(entry))
 				mpfn |= MIGRATE_PFN_WRITE;
 		} else {
-- 
2.20.1

CONFIG_MIGRATE_VMA_HELPER guards helpers that are required for proper
devic private memory support.  Remove the option and just check for
CONFIG_DEVICE_PRIVATE instead.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/gpu/drm/nouveau/Kconfig | 1 -
 mm/Kconfig                      | 3 ---
 mm/migrate.c                    | 4 ++--
 3 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/Kconfig b/drivers/gpu/drm/nouveau/Kconfig
index df4352c279ba..3558df043592 100644
--- a/drivers/gpu/drm/nouveau/Kconfig
+++ b/drivers/gpu/drm/nouveau/Kconfig
@@ -89,7 +89,6 @@ config DRM_NOUVEAU_SVM
 	depends on MMU
 	depends on STAGING
 	select HMM_MIRROR
-	select MIGRATE_VMA_HELPER
 	select MMU_NOTIFIER
 	default n
 	help
diff --git a/mm/Kconfig b/mm/Kconfig
index 563436dc1f24..2fe4902ad755 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -669,9 +669,6 @@ config ZONE_DEVICE
 
 	  If FS_DAX is enabled, then say Y.
 
-config MIGRATE_VMA_HELPER
-	bool
-
 config DEV_PAGEMAP_OPS
 	bool
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 33e063c28c1b..993386cb5335 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2117,7 +2117,7 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 
 #endif /* CONFIG_NUMA */
 
-#if defined(CONFIG_MIGRATE_VMA_HELPER)
+#ifdef CONFIG_DEVICE_PRIVATE
 static int migrate_vma_collect_hole(unsigned long start,
 				    unsigned long end,
 				    struct mm_walk *walk)
@@ -2942,4 +2942,4 @@ void migrate_vma_finalize(struct migrate_vma *migrate)
 	}
 }
 EXPORT_SYMBOL(migrate_vma_finalize);
-#endif /* defined(MIGRATE_VMA_HELPER) */
+#endif /* CONFIG_DEVICE_PRIVATE */
-- 
2.20.1

On 8/14/19 2:59 AM, Christoph Hellwig wrote:
> There isn't any good reason to pass callbacks to migrate_vma.  Instead
> we can just export the three steps done by this function to drivers and
> let them sequence the operation without callbacks.  This removes a lot
> of boilerplate code as-is, and will allow the drivers to drastically
> improve code flow and error handling further on.
>
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
> ---
>   Documentation/vm/hmm.rst               |  55 +-----
>   drivers/gpu/drm/nouveau/nouveau_dmem.c | 122 +++++++------
>   include/linux/migrate.h                | 118 ++----------
>   mm/migrate.c                           | 244 +++++++++++--------------
>   4 files changed, 195 insertions(+), 344 deletions(-)
>
> diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
> index e63c11f7e0e0..4f81c77059e3 100644
> --- a/Documentation/vm/hmm.rst
> +++ b/Documentation/vm/hmm.rst
> @@ -339,58 +339,9 @@ Migration to and from device memory
>   ==================================>   
>   Because the CPU cannot access device memory, migration must use the
device DMA
> -engine to perform copy from and to device memory. For this we need a new
> -migration helper::
> -
> - int migrate_vma(const struct migrate_vma_ops *ops,
> -                 struct vm_area_struct *vma,
> -                 unsigned long mentries,
> -                 unsigned long start,
> -                 unsigned long end,
> -                 unsigned long *src,
> -                 unsigned long *dst,
> -                 void *private);
> -
> -Unlike other migration functions it works on a range of virtual address,
there
> -are two reasons for that. First, device DMA copy has a high setup overhead
cost
> -and thus batching multiple pages is needed as otherwise the migration
overhead
> -makes the whole exercise pointless. The second reason is because the
> -migration might be for a range of addresses the device is actively
accessing.
> -
> -The migrate_vma_ops struct defines two callbacks. First one
(alloc_and_copy())
> -controls destination memory allocation and copy operation. Second one is
there
> -to allow the device driver to perform cleanup operations after migration::
> -
> - struct migrate_vma_ops {
> -     void (*alloc_and_copy)(struct vm_area_struct *vma,
> -                            const unsigned long *src,
> -                            unsigned long *dst,
> -                            unsigned long start,
> -                            unsigned long end,
> -                            void *private);
> -     void (*finalize_and_map)(struct vm_area_struct *vma,
> -                              const unsigned long *src,
> -                              const unsigned long *dst,
> -                              unsigned long start,
> -                              unsigned long end,
> -                              void *private);
> - };
> -
> -It is important to stress that these migration helpers allow for holes in
the
> -virtual address range. Some pages in the range might not be migrated for
all
> -the usual reasons (page is pinned, page is locked, ...). This helper does
not
> -fail but just skips over those pages.
> -
> -The alloc_and_copy() might decide to not migrate all pages in the
> -range (for reasons under the callback control). For those, the callback
just
> -has to leave the corresponding dst entry empty.
> -
> -Finally, the migration of the struct page might fail (for file backed
page) for
> -various reasons (failure to freeze reference, or update page cache, ...).
If
> -that happens, then the finalize_and_map() can catch any pages that were
not
> -migrated. Note those pages were still copied to a new page and thus we
wasted
> -bandwidth but this is considered as a rare event and a price that we are
> -willing to pay to keep all the code simpler.
> +engine to perform copy from and to device memory. For this we need a new
to
s/we need a new to/we need to/ ?
> +use migrate_vma_setup(), migrate_vma_pages(), and migrate_vma_finalize()
> +helpers.
>   
>   
>   Memory cgroup (memcg) and rss accounting
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 345c63cb752a..38416798abd4 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -131,9 +131,8 @@ nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct
*vma,
>   				  unsigned long *dst_pfns,
>   				  unsigned long start,
>   				  unsigned long end,
> -				  void *private)
> +				  struct nouveau_dmem_fault *fault)
>   {
> -	struct nouveau_dmem_fault *fault = private;
>   	struct nouveau_drm *drm = fault->drm;
>   	struct device *dev = drm->dev->dev;
>   	unsigned long addr, i, npages = 0;
> @@ -230,14 +229,9 @@ nouveau_dmem_fault_alloc_and_copy(struct
vm_area_struct *vma,
>   	}
>   }
>   
> -void nouveau_dmem_fault_finalize_and_map(struct vm_area_struct *vma,
> -					 const unsigned long *src_pfns,
> -					 const unsigned long *dst_pfns,
> -					 unsigned long start,
> -					 unsigned long end,
> -					 void *private)
> +static void
> +nouveau_dmem_fault_finalize_and_map(struct nouveau_dmem_fault *fault)
>   {
> -	struct nouveau_dmem_fault *fault = private;
>   	struct nouveau_drm *drm = fault->drm;
>   
>   	if (fault->fence) {
> @@ -257,29 +251,35 @@ void nouveau_dmem_fault_finalize_and_map(struct
vm_area_struct *vma,
>   	kfree(fault->dma);
>   }
>   
> -static const struct migrate_vma_ops nouveau_dmem_fault_migrate_ops = {
> -	.alloc_and_copy		= nouveau_dmem_fault_alloc_and_copy,
> -	.finalize_and_map	= nouveau_dmem_fault_finalize_and_map,
> -};
> -
>   static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
>   {
>   	struct nouveau_dmem *dmem = page_to_dmem(vmf->page);
>   	unsigned long src[1] = {0}, dst[1] = {0};
> +	struct migrate_vma args = {
> +		.vma		= vmf->vma,
> +		.start		= vmf->address,
> +		.end		= vmf->address + PAGE_SIZE,
> +		.src		= src,
> +		.dst		= dst,
> +	};
>   	struct nouveau_dmem_fault fault = { .drm = dmem->drm };
> -	int ret;
>   
>   	/*
>   	 * FIXME what we really want is to find some heuristic to migrate more
>   	 * than just one page on CPU fault. When such fault happens it is very
>   	 * likely that more surrounding page will CPU fault too.
>   	 */
> -	ret = migrate_vma(&nouveau_dmem_fault_migrate_ops, vmf->vma,
> -			vmf->address, vmf->address + PAGE_SIZE,
> -			src, dst, &fault);
> -	if (ret)
> +	if (migrate_vma_setup(&args) < 0)
>   		return VM_FAULT_SIGBUS;
> +	if (!args.cpages)
> +		return 0;
> +
> +	nouveau_dmem_fault_alloc_and_copy(args.vma, src, dst, args.start,
> +			args.end, &fault);
> +	migrate_vma_pages(&args);
> +	nouveau_dmem_fault_finalize_and_map(&fault);
>   
> +	migrate_vma_finalize(&args);
>   	if (dst[0] == MIGRATE_PFN_ERROR)
>   		return VM_FAULT_SIGBUS;
>   
> @@ -648,9 +648,8 @@ nouveau_dmem_migrate_alloc_and_copy(struct
vm_area_struct *vma,
>   				    unsigned long *dst_pfns,
>   				    unsigned long start,
>   				    unsigned long end,
> -				    void *private)
> +				    struct nouveau_migrate *migrate)
>   {
> -	struct nouveau_migrate *migrate = private;
>   	struct nouveau_drm *drm = migrate->drm;
>   	struct device *dev = drm->dev->dev;
>   	unsigned long addr, i, npages = 0;
> @@ -747,14 +746,9 @@ nouveau_dmem_migrate_alloc_and_copy(struct
vm_area_struct *vma,
>   	}
>   }
>   
> -void nouveau_dmem_migrate_finalize_and_map(struct vm_area_struct *vma,
> -					   const unsigned long *src_pfns,
> -					   const unsigned long *dst_pfns,
> -					   unsigned long start,
> -					   unsigned long end,
> -					   void *private)
> +static void
> +nouveau_dmem_migrate_finalize_and_map(struct nouveau_migrate *migrate)
>   {
> -	struct nouveau_migrate *migrate = private;
>   	struct nouveau_drm *drm = migrate->drm;
>   
>   	if (migrate->fence) {
> @@ -779,10 +773,15 @@ void nouveau_dmem_migrate_finalize_and_map(struct
vm_area_struct *vma,
>   	 */
>   }
>   
> -static const struct migrate_vma_ops nouveau_dmem_migrate_ops = {
> -	.alloc_and_copy		= nouveau_dmem_migrate_alloc_and_copy,
> -	.finalize_and_map	= nouveau_dmem_migrate_finalize_and_map,
> -};
> +static void nouveau_dmem_migrate_chunk(struct migrate_vma *args,
> +		struct nouveau_migrate *migrate)
> +{
> +	nouveau_dmem_migrate_alloc_and_copy(args->vma, args->src,
args->dst,
> +			args->start, args->end, migrate);
> +	migrate_vma_pages(args);
> +	nouveau_dmem_migrate_finalize_and_map(migrate);
> +	migrate_vma_finalize(args);
> +}
>   
>   int
>   nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
> @@ -790,40 +789,45 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
>   			 unsigned long start,
>   			 unsigned long end)
>   {
> -	unsigned long *src_pfns, *dst_pfns, npages;
> -	struct nouveau_migrate migrate = {0};
> -	unsigned long i, c, max;
> -	int ret = 0;
> -
> -	npages = (end - start) >> PAGE_SHIFT;
> -	max = min(SG_MAX_SINGLE_ALLOC, npages);
> -	src_pfns = kzalloc(sizeof(long) * max, GFP_KERNEL);
> -	if (src_pfns == NULL)
> -		return -ENOMEM;
> -	dst_pfns = kzalloc(sizeof(long) * max, GFP_KERNEL);
> -	if (dst_pfns == NULL) {
> -		kfree(src_pfns);
> -		return -ENOMEM;
> -	}
> +	unsigned long npages = (end - start) >> PAGE_SHIFT;
> +	unsigned long max = min(SG_MAX_SINGLE_ALLOC, npages);
> +	struct migrate_vma args = {
> +		.vma		= vma,
> +		.start		= start,
> +	};
> +	struct nouveau_migrate migrate = {
> +		.drm		= drm,
> +		.vma		= vma,
> +		.npages		= npages,
> +	};
> +	unsigned long c, i;
> +	int ret = -ENOMEM;
> +
> +	args.src = kzalloc(sizeof(long) * max, GFP_KERNEL);
> +	if (!args.src)
> +		goto out;
> +	args.dst = kzalloc(sizeof(long) * max, GFP_KERNEL);
> +	if (!args.dst)
> +		goto out_free_src;
>   
> -	migrate.drm = drm;
> -	migrate.vma = vma;
> -	migrate.npages = npages;
>   	for (i = 0; i < npages; i += c) {
> -		unsigned long next;
> -
>   		c = min(SG_MAX_SINGLE_ALLOC, npages);
> -		next = start + (c << PAGE_SHIFT);
> -		ret = migrate_vma(&nouveau_dmem_migrate_ops, vma, start,
> -				  next, src_pfns, dst_pfns, &migrate);
> +		args.end = start + (c << PAGE_SHIFT);
> +		ret = migrate_vma_setup(&args);
>   		if (ret)
> -			goto out;
> -		start = next;
> +			goto out_free_dst;
> +
> +		if (args.cpages)
> +			nouveau_dmem_migrate_chunk(&args, &migrate);
> +		args.start = args.end;
>   	}
>   
> +	ret = 0;
> +out_free_dst:
> +	kfree(args.dst);
> +out_free_src:
> +	kfree(args.src);
>   out:
> -	kfree(dst_pfns);
> -	kfree(src_pfns);
>   	return ret;
>   }
>   
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 7f04754c7f2b..18156d379ebf 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -182,107 +182,27 @@ static inline unsigned long migrate_pfn(unsigned
long pfn)
>   	return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID;
>   }
>   
> -/*
> - * struct migrate_vma_ops - migrate operation callback
> - *
> - * @alloc_and_copy: alloc destination memory and copy source memory to it
> - * @finalize_and_map: allow caller to map the successfully migrated pages
> - *
> - *
> - * The alloc_and_copy() callback happens once all source pages have been
locked,
> - * unmapped and checked (checked whether pinned or not). All pages that
can be
> - * migrated will have an entry in the src array set with the pfn value of
the
> - * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set
(other
> - * flags might be set but should be ignored by the callback).
> - *
> - * The alloc_and_copy() callback can then allocate destination memory and
copy
> - * source memory to it for all those entries (ie with MIGRATE_PFN_VALID
and
> - * MIGRATE_PFN_MIGRATE flag set). Once these are allocated and copied, the
> - * callback must update each corresponding entry in the dst array with the
pfn
> - * value of the destination page and with the MIGRATE_PFN_VALID and
> - * MIGRATE_PFN_LOCKED flags set (destination pages must have their struct
pages
> - * locked, via lock_page()).
> - *
> - * At this point the alloc_and_copy() callback is done and returns.
> - *
> - * Note that the callback does not have to migrate all the pages that are
> - * marked with MIGRATE_PFN_MIGRATE flag in src array unless this is a
migration
> - * from device memory to system memory (ie the MIGRATE_PFN_DEVICE flag is
also
> - * set in the src array entry). If the device driver cannot migrate a
device
> - * page back to system memory, then it must set the corresponding dst
array
> - * entry to MIGRATE_PFN_ERROR. This will trigger a SIGBUS if CPU tries to
> - * access any of the virtual addresses originally backed by this page.
Because
> - * a SIGBUS is such a severe result for the userspace process, the device
> - * driver should avoid setting MIGRATE_PFN_ERROR unless it is really in an
> - * unrecoverable state.
> - *
> - * For empty entry inside CPU page table (pte_none() or pmd_none() is
true) we
> - * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array
thus
> - * allowing device driver to allocate device memory for those unback
virtual
> - * address. For this the device driver simply have to allocate device
memory
> - * and properly set the destination entry like for regular migration. Note
that
> - * this can still fails and thus inside the device driver must check if
the
> - * migration was successful for those entry inside the finalize_and_map()
> - * callback just like for regular migration.
> - *
> - * THE alloc_and_copy() CALLBACK MUST NOT CHANGE ANY OF THE SRC ARRAY
ENTRIES
> - * OR BAD THINGS WILL HAPPEN !
> - *
> - *
> - * The finalize_and_map() callback happens after struct page migration
from
> - * source to destination (destination struct pages are the struct pages
for the
> - * memory allocated by the alloc_and_copy() callback).  Migration can
fail, and
> - * thus the finalize_and_map() allows the driver to inspect which pages
were
> - * successfully migrated, and which were not. Successfully migrated pages
will
> - * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
> - *
> - * It is safe to update device page table from within the
finalize_and_map()
> - * callback because both destination and source page are still locked, and
the
> - * mmap_sem is held in read mode (hence no one can unmap the range being
> - * migrated).
> - *
> - * Once callback is done cleaning up things and updating its page table
(if it
> - * chose to do so, this is not an obligation) then it returns. At this
point,
> - * the HMM core will finish up the final steps, and the migration is
complete.
> - *
> - * THE finalize_and_map() CALLBACK MUST NOT CHANGE ANY OF THE SRC OR DST
ARRAY
> - * ENTRIES OR BAD THINGS WILL HAPPEN !
> - */
> -struct migrate_vma_ops {
> -	void (*alloc_and_copy)(struct vm_area_struct *vma,
> -			       const unsigned long *src,
> -			       unsigned long *dst,
> -			       unsigned long start,
> -			       unsigned long end,
> -			       void *private);
> -	void (*finalize_and_map)(struct vm_area_struct *vma,
> -				 const unsigned long *src,
> -				 const unsigned long *dst,
> -				 unsigned long start,
> -				 unsigned long end,
> -				 void *private);
> +struct migrate_vma {
> +	struct vm_area_struct	*vma;
> +	/*
> +	 * Both src and dst array must be big enough for
> +	 * (end - start) >> PAGE_SHIFT entries.
> +	 *
> +	 * The src array must not be modified by the caller after
> +	 * migrate_vma_setup(), and must not change the dst array after
> +	 * migrate_vma_pages() returns.
> +	 */
> +	unsigned long		*dst;
> +	unsigned long		*src;
> +	unsigned long		cpages;
> +	unsigned long		npages;
> +	unsigned long		start;
> +	unsigned long		end;
>   };
>   
> -#if defined(CONFIG_MIGRATE_VMA_HELPER)
> -int migrate_vma(const struct migrate_vma_ops *ops,
> -		struct vm_area_struct *vma,
> -		unsigned long start,
> -		unsigned long end,
> -		unsigned long *src,
> -		unsigned long *dst,
> -		void *private);
> -#else
> -static inline int migrate_vma(const struct migrate_vma_ops *ops,
> -			      struct vm_area_struct *vma,
> -			      unsigned long start,
> -			      unsigned long end,
> -			      unsigned long *src,
> -			      unsigned long *dst,
> -			      void *private)
> -{
> -	return -EINVAL;
> -}
> -#endif /* IS_ENABLED(CONFIG_MIGRATE_VMA_HELPER) */
> +int migrate_vma_setup(struct migrate_vma *args);
> +void migrate_vma_pages(struct migrate_vma *migrate);
> +void migrate_vma_finalize(struct migrate_vma *migrate);
>   
>   #endif /* CONFIG_MIGRATION */
>   
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 8992741f10aa..e2565374d330 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2118,16 +2118,6 @@ int migrate_misplaced_transhuge_page(struct
mm_struct *mm,
>   #endif /* CONFIG_NUMA */
>   
>   #if defined(CONFIG_MIGRATE_VMA_HELPER)
> -struct migrate_vma {
> -	struct vm_area_struct	*vma;
> -	unsigned long		*dst;
> -	unsigned long		*src;
> -	unsigned long		cpages;
> -	unsigned long		npages;
> -	unsigned long		start;
> -	unsigned long		end;
> -};
> -
>   static int migrate_vma_collect_hole(unsigned long start,
>   				    unsigned long end,
>   				    struct mm_walk *walk)
> @@ -2578,6 +2568,110 @@ static void migrate_vma_unmap(struct migrate_vma
*migrate)
>   	}
>   }
>   
> +/**
> + * migrate_vma_setup() - prepare to migrate a range of memory
> + * @args: contains the vma, start, and and pfns arrays for the migration
> + *
> + * Returns: negative errno on failures, 0 when 0 or more pages were
migrated
> + * without an error.
> + *
> + * Prepare to migrate a range of memory virtual address range by
collecting all
> + * the pages backing each virtual address in the range, saving them inside
the
> + * src array.  Then lock those pages and unmap them. Once the pages are
locked
> + * and unmapped, check whether each page is pinned or not.  Pages that
aren't
> + * pinned have the MIGRATE_PFN_MIGRATE flag set (by this function) in the
> + * corresponding src array entry.  Then restores any pages that are
pinned, by
> + * remapping and unlocking those pages.
> + *
> + * The caller should then allocate destination memory and copy source
memory to
> + * it for all those entries (ie with MIGRATE_PFN_VALID and
MIGRATE_PFN_MIGRATE
> + * flag set).  Once these are allocated and copied, the caller must update
each
> + * corresponding entry in the dst array with the pfn value of the
destination
> + * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_LOCKED flags set
> + * (destination pages must have their struct pages locked, via
lock_page()).
> + *
> + * Note that the caller does not have to migrate all the pages that are
marked
> + * with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration
from
> + * device memory to system memory.  If the caller cannot migrate a device
page
> + * back to system memory, then it must return VM_FAULT_SIGBUS, which has
severe
> + * consequences for the userspace process, so it must be avoided if at all
> + * possible.
> + *
> + * For empty entries inside CPU page table (pte_none() or pmd_none() is
true) we
> + * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array
thus
> + * allowing the caller to allocate device memory for those unback virtual
> + * address.  For this the caller simply has to allocate device memory and
> + * properly set the destination entry like for regular migration.  Note
that
> + * this can still fails and thus inside the device driver must check if
the
> + * migration was successful for those entries after calling
migrate_vma_pages()
> + * just like for regular migration.
> + *
> + * After that, the callers must call migrate_vma_pages() to go over each
entry
> + * in the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
flag
> + * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag
set,
> + * then migrate_vma_pages() to migrate struct page information from the
source
> + * struct page to the destination struct page.  If it fails to migrate the
> + * struct page information, then it clears the MIGRATE_PFN_MIGRATE flag in
the
> + * src array.
> + *
> + * At this point all successfully migrated pages have an entry in the src
> + * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the
dst
> + * array entry with MIGRATE_PFN_VALID flag set.
> + *
> + * Once migrate_vma_pages() returns the caller may inspect which pages
were
> + * successfully migrated, and which were not.  Successfully migrated pages
will
> + * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
> + *
> + * It is safe to update device page table from within the
finalize_and_map()
> + * callback because both destination and source page are still locked, and
the
> + * mmap_sem is held in read mode (hence no one can unmap the range being
> + * migrated).
> + *
> + * Once the caller is done cleaning up things and updating its page table
(if it
> + * chose to do so, this is not an obligation) it finally calls
> + * migrate_vma_finalize() to update the CPU page table to point to new
pages
> + * for successfully migrated pages or otherwise restore the CPU page table
to
> + * point to the original source pages.
> + */
> +int migrate_vma_setup(struct migrate_vma *args)
> +{
> +	long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
> +
> +	args->start &= PAGE_MASK;
> +	args->end &= PAGE_MASK;
> +	if (!args->vma || is_vm_hugetlb_page(args->vma) ||
> +	    (args->vma->vm_flags & VM_SPECIAL) ||
vma_is_dax(args->vma))
> +		return -EINVAL;
> +	if (nr_pages <= 0)
> +		return -EINVAL;
> +	if (args->start < args->vma->vm_start ||
> +	    args->start >= args->vma->vm_end)
> +		return -EINVAL;
> +	if (args->end <= args->vma->vm_start || args->end >
args->vma->vm_end)
> +		return -EINVAL;
> +	if (!args->src || !args->dst)
> +		return -EINVAL;
> +
> +	memset(args->src, 0, sizeof(*args->src) * nr_pages);
> +	args->cpages = 0;
> +	args->npages = 0;
> +
> +	migrate_vma_collect(args);
> +	if (args->cpages)
> +		migrate_vma_prepare(args);
> +	if (args->cpages)
> +		migrate_vma_unmap(args);
> +
> +	/*
> +	 * At this point pages are locked and unmapped, and thus they have
> +	 * stable content and can safely be copied to destination memory that
> +	 * is allocated by the drivers.
> +	 */
> +	return 0;
> +
> +}
> +EXPORT_SYMBOL(migrate_vma_setup);
> +
>   static void migrate_vma_insert_page(struct migrate_vma *migrate,
>   				    unsigned long addr,
>   				    struct page *page,
> @@ -2709,7 +2803,7 @@ static void migrate_vma_insert_page(struct
migrate_vma *migrate,
>   	*src &= ~MIGRATE_PFN_MIGRATE;
>   }
>   
> -/*
> +/**
>    * migrate_vma_pages() - migrate meta-data from src page to dst page
>    * @migrate: migrate struct containing all migration information
>    *
> @@ -2717,7 +2811,7 @@ static void migrate_vma_insert_page(struct
migrate_vma *migrate,
>    * struct page. This effectively finishes the migration from source page
to the
>    * destination page.
>    */
> -static void migrate_vma_pages(struct migrate_vma *migrate)
> +void migrate_vma_pages(struct migrate_vma *migrate)
>   {
>   	const unsigned long npages = migrate->npages;
>   	const unsigned long start = migrate->start;
> @@ -2791,8 +2885,9 @@ static void migrate_vma_pages(struct migrate_vma
*migrate)
>   	if (notified)
>   		mmu_notifier_invalidate_range_only_end(&range);
>   }
> +EXPORT_SYMBOL(migrate_vma_pages);
>   
> -/*
> +/**
>    * migrate_vma_finalize() - restore CPU page table entry
>    * @migrate: migrate struct containing all migration information
>    *
> @@ -2803,7 +2898,7 @@ static void migrate_vma_pages(struct migrate_vma
*migrate)
>    * This also unlocks the pages and puts them back on the lru, or drops
the extra
>    * refcount, for device pages.
>    */
> -static void migrate_vma_finalize(struct migrate_vma *migrate)
> +void migrate_vma_finalize(struct migrate_vma *migrate)
>   {
>   	const unsigned long npages = migrate->npages;
>   	unsigned long i;
> @@ -2846,124 +2941,5 @@ static void migrate_vma_finalize(struct migrate_vma
*migrate)
>   		}
>   	}
>   }
> -
> -/*
> - * migrate_vma() - migrate a range of memory inside vma
> - *
> - * @ops: migration callback for allocating destination memory and copying
> - * @vma: virtual memory area containing the range to be migrated
> - * @start: start address of the range to migrate (inclusive)
> - * @end: end address of the range to migrate (exclusive)
> - * @src: array of hmm_pfn_t containing source pfns
> - * @dst: array of hmm_pfn_t containing destination pfns
> - * @private: pointer passed back to each of the callback
> - * Returns: 0 on success, error code otherwise
> - *
> - * This function tries to migrate a range of memory virtual address range,
using
> - * callbacks to allocate and copy memory from source to destination. First
it
> - * collects all the pages backing each virtual address in the range,
saving this
> - * inside the src array. Then it locks those pages and unmaps them. Once
the pages
> - * are locked and unmapped, it checks whether each page is pinned or not.
Pages
> - * that aren't pinned have the MIGRATE_PFN_MIGRATE flag set (by this
function)
> - * in the corresponding src array entry. It then restores any pages that
are
> - * pinned, by remapping and unlocking those pages.
> - *
> - * At this point it calls the alloc_and_copy() callback. For documentation
on
> - * what is expected from that callback, see struct migrate_vma_ops
comments in
> - * include/linux/migrate.h
> - *
> - * After the alloc_and_copy() callback, this function goes over each entry
in
> - * the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
flag
> - * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag
set,
> - * then the function tries to migrate struct page information from the
source
> - * struct page to the destination struct page. If it fails to migrate the
struct
> - * page information, then it clears the MIGRATE_PFN_MIGRATE flag in the
src
> - * array.
> - *
> - * At this point all successfully migrated pages have an entry in the src
> - * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the
dst
> - * array entry with MIGRATE_PFN_VALID flag set.
> - *
> - * It then calls the finalize_and_map() callback. See comments for
"struct
> - * migrate_vma_ops", in include/linux/migrate.h for details about
> - * finalize_and_map() behavior.
> - *
> - * After the finalize_and_map() callback, for successfully migrated pages,
this
> - * function updates the CPU page table to point to new pages, otherwise it
> - * restores the CPU page table to point to the original source pages.
> - *
> - * Function returns 0 after the above steps, even if no pages were
migrated
> - * (The function only returns an error if any of the arguments are
invalid.)
> - *
> - * Both src and dst array must be big enough for (end - start) >>
PAGE_SHIFT
> - * unsigned long entries.
> - */
> -int migrate_vma(const struct migrate_vma_ops *ops,
> -		struct vm_area_struct *vma,
> -		unsigned long start,
> -		unsigned long end,
> -		unsigned long *src,
> -		unsigned long *dst,
> -		void *private)
> -{
> -	struct migrate_vma migrate;
> -
> -	/* Sanity check the arguments */
> -	start &= PAGE_MASK;
> -	end &= PAGE_MASK;
> -	if (!vma || is_vm_hugetlb_page(vma) || (vma->vm_flags &
VM_SPECIAL) ||
> -			vma_is_dax(vma))
> -		return -EINVAL;
> -	if (start < vma->vm_start || start >= vma->vm_end)
> -		return -EINVAL;
> -	if (end <= vma->vm_start || end > vma->vm_end)
> -		return -EINVAL;
> -	if (!ops || !src || !dst || start >= end)
> -		return -EINVAL;
> -
> -	memset(src, 0, sizeof(*src) * ((end - start) >> PAGE_SHIFT));
> -	migrate.src = src;
> -	migrate.dst = dst;
> -	migrate.start = start;
> -	migrate.npages = 0;
> -	migrate.cpages = 0;
> -	migrate.end = end;
> -	migrate.vma = vma;
> -
> -	/* Collect, and try to unmap source pages */
> -	migrate_vma_collect(&migrate);
> -	if (!migrate.cpages)
> -		return 0;
> -
> -	/* Lock and isolate page */
> -	migrate_vma_prepare(&migrate);
> -	if (!migrate.cpages)
> -		return 0;
> -
> -	/* Unmap pages */
> -	migrate_vma_unmap(&migrate);
> -	if (!migrate.cpages)
> -		return 0;
> -
> -	/*
> -	 * At this point pages are locked and unmapped, and thus they have
> -	 * stable content and can safely be copied to destination memory that
> -	 * is allocated by the callback.
> -	 *
> -	 * Note that migration can fail in migrate_vma_struct_page() for each
> -	 * individual page.
> -	 */
> -	ops->alloc_and_copy(vma, src, dst, start, end, private);
> -
> -	/* This does the real migration of struct page */
> -	migrate_vma_pages(&migrate);
> -
> -	ops->finalize_and_map(vma, src, dst, start, end, private);
> -
> -	/* Unlock and remap pages */
> -	migrate_vma_finalize(&migrate);
> -
> -	return 0;
> -}
> -EXPORT_SYMBOL(migrate_vma);
> +EXPORT_SYMBOL(migrate_vma_finalize);
>   #endif /* defined(MIGRATE_VMA_HELPER) */

On 8/14/19 12:59 AM, Christoph Hellwig wrote:
> Hi Jérôme, Ben and Jason,
> 
> below is a series against the hmm tree which starts revamping the
> migrate_vma functionality.  The prime idea is to export three slightly
> lower level functions and thus avoid the need for migrate_vma_ops
> callbacks.
> 
> Diffstat:
> 
>      7 files changed, 282 insertions(+), 614 deletions(-)
> 
> A git tree is also available at:
> 
>      git://git.infradead.org/users/hch/misc.git migrate_vma-cleanup.3
> 
> Gitweb:
> 
>     
http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/migrate_vma-cleanup.3
> 
> 
> Changes since v2:
>   - don't unmap pages when returning 0 from nouveau_dmem_migrate_to_ram
>   - minor style fixes
>   - add a new patch to remove CONFIG_MIGRATE_VMA_HELPER
> 
> Changes since v1:
>   - fix a few whitespace issues
>   - drop the patch to remove MIGRATE_PFN_WRITE for now
>   - various spelling fixes
>   - clear cpages and npages in migrate_vma_setup
>   - fix the nouveau_dmem_fault_copy_one return value
>   - minor improvements to some nouveau internal calling conventions
> 
Some of the patches seem to have been mangled in the mail.
I was able to edit them and apply to Jason's tree
https://github.com/jgunthorpe/linux.git mmu_notifier branch.
So for the series you can add:

Tested-by: Ralph Campbell <rcampbell at nvidia.com>

On Wed, Aug 14, 2019 at 05:09:54PM -0700, Ralph Campbell
wrote:
> Some of the patches seem to have been mangled in the mail.
Weird, I never had such a an issue with git-send-email.

But to be covered for such weird cases I also posted a git url
for exactly the tree I've been working on.
> I was able to edit them and apply to Jason's tree
> https://github.com/jgunthorpe/linux.git mmu_notifier branch.
> So for the series you can add:
>
> Tested-by: Ralph Campbell <rcampbell at nvidia.com>
Thanks!

Jason,

are you going to look into picking this up?  Unfortunately there is
a hole pile in this area still pending, including the kvmppc secure
memory driver from Bharata that depends on the work.

mm folks:  migrate.c is mostly a classic MM file except for the hmm
additions.  Do you want to also look over this or just let it pass?

On Fri, Aug 16, 2019 at 08:51:41AM +0200, Christoph Hellwig
wrote:
> Jason,
> 
> are you going to look into picking this up?  Unfortunately there is
> a hole pile in this area still pending, including the kvmppc secure
> memory driver from Bharata that depends on the work.
> 
> mm folks:  migrate.c is mostly a classic MM file except for the hmm
> additions.  Do you want to also look over this or just let it pass?
Yes, after you explained the functions were hmm ones, it seems OK to
go to hmm.git.

I was waiting for the dust to settle, I see Ralph tested-by, are we
good now?

Jason

On Wed, Aug 14, 2019 at 09:59:28AM +0200, Christoph Hellwig
wrote:
> CONFIG_MIGRATE_VMA_HELPER guards helpers that are required for proper
> devic private memory support.  Remove the option and just check for
> CONFIG_DEVICE_PRIVATE instead.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  drivers/gpu/drm/nouveau/Kconfig | 1 -
>  mm/Kconfig                      | 3 ---
>  mm/migrate.c                    | 4 ++--
>  3 files changed, 2 insertions(+), 6 deletions(-)
Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>

Aside from it making sense, I checked no other driver enables
DEVICE_PRIVATE, so no change in kernel build.

Jason

On Wed, Aug 14, 2019 at 09:59:27AM +0200, Christoph Hellwig
wrote:
> No one ever checks this flag, and we could easily get that information
> from the page if needed.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_dmem.c | 3 +--
>  include/linux/migrate.h                | 1 -
>  mm/migrate.c                           | 4 ++--
>  3 files changed, 3 insertions(+), 5 deletions(-)
Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>

Jason

On Wed, Aug 14, 2019 at 09:59:19AM +0200, Christoph Hellwig
wrote:
> There isn't any good reason to pass callbacks to migrate_vma.  Instead
> we can just export the three steps done by this function to drivers and
> let them sequence the operation without callbacks.  This removes a lot
> of boilerplate code as-is, and will allow the drivers to drastically
> improve code flow and error handling further on.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
> ---
>  Documentation/vm/hmm.rst               |  55 +-----
>  drivers/gpu/drm/nouveau/nouveau_dmem.c | 122 +++++++------
>  include/linux/migrate.h                | 118 ++----------
>  mm/migrate.c                           | 244 +++++++++++--------------
>  4 files changed, 195 insertions(+), 344 deletions(-)
The mechanical transformation looks OK, I squashed the below nits in,
let me know if I got it wrong

Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 4f81c77059e305..0a5960beccf76d 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -339,9 +339,8 @@ Migration to and from device memory
 ================================== 
 Because the CPU cannot access device memory, migration must use the device DMA
-engine to perform copy from and to device memory. For this we need a new to
-use migrate_vma_setup(), migrate_vma_pages(), and migrate_vma_finalize()
-helpers.
+engine to perform copy from and to device memory. For this we need to use
+migrate_vma_setup(), migrate_vma_pages(), and migrate_vma_finalize() helpers.
 
 
 Memory cgroup (memcg) and rss accounting
diff --git a/mm/migrate.c b/mm/migrate.c
index 993386cb53358d..0e78ebd720c0e4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2622,10 +2622,9 @@ static void migrate_vma_unmap(struct migrate_vma
*migrate)
  * successfully migrated, and which were not.  Successfully migrated pages will
  * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
  *
- * It is safe to update device page table from within the finalize_and_map()
- * callback because both destination and source page are still locked, and the
- * mmap_sem is held in read mode (hence no one can unmap the range being
- * migrated).
+ * It is safe to update device page table after migrate_vma_pages() because
+ * both destination and source page are still locked, and the mmap_sem is held
+ * in read mode (hence no one can unmap the range being migrated).
  *
  * Once the caller is done cleaning up things and updating its page table (if
it
  * chose to do so, this is not an obligation) it finally calls
@@ -2657,10 +2656,11 @@ int migrate_vma_setup(struct migrate_vma *args)
 	args->npages = 0;
 
 	migrate_vma_collect(args);
-	if (args->cpages)
-		migrate_vma_prepare(args);
-	if (args->cpages)
-		migrate_vma_unmap(args);
+	if (!args->cpages)
+		return 0;
+
+	migrate_vma_prepare(args);
+	migrate_vma_unmap(args);
 
 	/*
 	 * At this point pages are locked and unmapped, and thus they have

On Wed, Aug 14, 2019 at 09:59:18AM +0200, Christoph Hellwig
wrote:
> Hi Jérôme, Ben and Jason,
> 
> below is a series against the hmm tree which starts revamping the
> migrate_vma functionality.  The prime idea is to export three slightly
> lower level functions and thus avoid the need for migrate_vma_ops
> callbacks.
> 
> Diffstat:
> 
>     7 files changed, 282 insertions(+), 614 deletions(-)
Yay, another big wack of code gone
 
Applied to hmm.git

Thanks,
Jason

On Fri, Aug 16, 2019 at 08:51:41AM +0200, Christoph Hellwig
wrote:
> Jason,
> 
> are you going to look into picking this up?  Unfortunately there is
> a hole pile in this area still pending, including the kvmppc secure
> memory driver from Bharata that depends on the work.
Done,

Lets see if Dan will comment on the pagemap part (looks
straightforward to me), and then after we grab that I will declare
hmm.git non-rebasing and Bharata can build his series upon it.

As a reminder, please do not send hmm.git inside another pull request
to Linus without making it very clear in that cover letter and Cc'ing
me. Thanks.

Regards,
Jason