1 files changed, 104 insertions, 0 deletions

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 7db4c812a2a6..8f73cebfc3f5 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -156,4 +156,108 @@ static inline int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 }
 #endif /* CONFIG_NUMA_BALANCING && CONFIG_TRANSPARENT_HUGEPAGE*/
 
+
+#ifdef CONFIG_MIGRATION
+
+#define MIGRATE_PFN_VALID       (1UL << 0)
+#define MIGRATE_PFN_MIGRATE     (1UL << 1)
+#define MIGRATE_PFN_LOCKED      (1UL << 2)
+#define MIGRATE_PFN_WRITE       (1UL << 3)
+#define MIGRATE_PFN_ERROR       (1UL << 4)
+#define MIGRATE_PFN_SHIFT       5
+
+static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
+{
+        if (!(mpfn & MIGRATE_PFN_VALID))
+                return NULL;
+        return pfn_to_page(mpfn >> MIGRATE_PFN_SHIFT);
+}
+
+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.
+ *
+ * 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);
+};
+
+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);
+
+#endif /* CONFIG_MIGRATION */
+
 #endif /* _LINUX_MIGRATE_H */