mm/migrate: Add migrate_device_pfns

JIRA: https://issues.redhat.com/browse/RHEL-113204

commit a14fa8e
Author: Matthew Brost <matthew.brost@intel.com>
Date:   Wed Mar 5 17:26:27 2025 -0800

    mm/migrate: Add migrate_device_pfns

    Add migrate_device_pfns which prepares an array of pre-populated device
    pages for migration. This is needed for eviction of known set of
    non-contiguous devices pages to cpu pages which is a common case for SVM
    in DRM drivers using TTM.

    v2:
     - s/migrate_device_vma_range/migrate_device_prepopulated_range
     - Drop extra mmu invalidation (Vetter)
    v3:
     - s/migrate_device_prepopulated_range/migrate_device_pfns (Alistar)
     - Use helper to lock device pages (Alistar)
     - Update commit message with why this is required (Alistar)

    Cc: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Matthew Brost <matthew.brost@intel.com>
    Reviewed-by: Alistair Popple <apopple@nvidia.com>
    Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20250306012657.3505757-3-matthew.brost@intel.com

Signed-off-by: José Expósito <jexposit@redhat.com>

Author: jexposit

include/linux/migrate.h

@@ -222,6 +222,7 @@ void migrate_vma_pages(struct migrate_vma *migrate);
 void migrate_vma_finalize(struct migrate_vma *migrate);
 int migrate_device_range(unsigned long *src_pfns, unsigned long start,
 			unsigned long npages);
+int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages);
 void migrate_device_pages(unsigned long *src_pfns, unsigned long *dst_pfns,
 			unsigned long npages);
 void migrate_device_finalize(unsigned long *src_pfns,

mm/migrate_device.c

@@ -870,6 +870,22 @@ void migrate_vma_finalize(struct migrate_vma *migrate)
 }
 EXPORT_SYMBOL(migrate_vma_finalize);
 
+static unsigned long migrate_device_pfn_lock(unsigned long pfn)
+{
+	struct folio *folio;
+
+	folio = folio_get_nontail_page(pfn_to_page(pfn));
+	if (!folio)
+		return 0;
+
+	if (!folio_trylock(folio)) {
+		folio_put(folio);
+		return 0;
+	}
+
+	return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
+}
+
 /**
  * migrate_device_range() - migrate device private pfns to normal memory.
  * @src_pfns: array large enough to hold migrating source device private pfns.
@@ -894,29 +910,35 @@ int migrate_device_range(unsigned long *src_pfns, unsigned long start,
 {
 	unsigned long i, pfn;
 
-	for (pfn = start, i = 0; i < npages; pfn++, i++) {
-		struct folio *folio;
+	for (pfn = start, i = 0; i < npages; pfn++, i++)
+		src_pfns[i] = migrate_device_pfn_lock(pfn);
 
-		folio = folio_get_nontail_page(pfn_to_page(pfn));
-		if (!folio) {
-			src_pfns[i] = 0;
-			continue;
-		}
+	migrate_device_unmap(src_pfns, npages, NULL);
 
-		if (!folio_trylock(folio)) {
-			src_pfns[i] = 0;
-			folio_put(folio);
-			continue;
-		}
+	return 0;
+}
+EXPORT_SYMBOL(migrate_device_range);
 
-		src_pfns[i] = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
-	}
+/**
+ * migrate_device_pfns() - migrate device private pfns to normal memory.
+ * @src_pfns: pre-popluated array of source device private pfns to migrate.
+ * @npages: number of pages to migrate.
+ *
+ * Similar to migrate_device_range() but supports non-contiguous pre-popluated
+ * array of device pages to migrate.
+ */
+int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages)
+{
+	unsigned long i;
+
+	for (i = 0; i < npages; i++)
+		src_pfns[i] = migrate_device_pfn_lock(src_pfns[i]);
 
 	migrate_device_unmap(src_pfns, npages, NULL);
 
 	return 0;
 }
-EXPORT_SYMBOL(migrate_device_range);
+EXPORT_SYMBOL(migrate_device_pfns);
 
 /*
  * Migrate a device coherent folio back to normal memory. The caller should have