---
 include/linux/page-flags.h |  5 +++++
 mm/util.c                  | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index b8c56672a588..e3d00c72f459 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h

@@ -767,6 +767,11 @@ PAGE_TYPE_OPS(Buddy, buddy)
  */
 PAGE_TYPE_OPS(Offline, offline)
 
+extern void page_offline_freeze(void);
+extern void page_offline_unfreeze(void);
+extern void page_offline_begin(void);
+extern void page_offline_end(void);
+
 /*
  * Marks pages in use as page tables.
  */

diff --git a/mm/util.c b/mm/util.c
index 54870226cea6..95395d4e4209 100644
--- a/mm/util.c
+++ b/mm/util.c

@@ -1013,3 +1013,41 @@ void mem_dump_obj(void *object)
 	}
 	pr_cont(" non-slab/vmalloc memory.\n");
 }
+
+/*
+ * A driver might set a page logically offline -- PageOffline() -- and
+ * turn the page inaccessible in the hypervisor; after that, access to page
+ * content can be fatal.
+ *
+ * Some special PFN walkers -- i.e., /proc/kcore -- read content of random
+ * pages after checking PageOffline(); however, these PFN walkers can race
+ * with drivers that set PageOffline().
+ *
+ * page_offline_freeze()/page_offline_unfreeze() allows for a subsystem to
+ * synchronize with such drivers, achieving that a page cannot be set
+ * PageOffline() while frozen.
+ *
+ * page_offline_begin()/page_offline_end() is used by drivers that care about
+ * such races when setting a page PageOffline().
+ */
+static DECLARE_RWSEM(page_offline_rwsem);
+
+void page_offline_freeze(void)
+{
+	down_read(&page_offline_rwsem);
+}
+
+void page_offline_unfreeze(void)
+{
+	up_read(&page_offline_rwsem);
+}
+
+void page_offline_begin(void)
+{
+	down_write(&page_offline_rwsem);
+}
+
+void page_offline_end(void)
+{
+	up_write(&page_offline_rwsem);
+}

-- 
2.30.2