This basically restores slightly modified version of original
sync_global_pgds() which we had before foldedl p4d was introduced.

The only modification is protection against 'address' overflow.

Signed-off-by: Kirill A. Shutemov <redacted>
---
 arch/x86/mm/init_64.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a991f5c4c2c4..d637893ac8c2 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c

@@ -92,6 +92,52 @@ __setup("noexec32=", nonx32_setup);
  * When memory was added/removed make sure all the processes MM have
  * suitable PGD entries in the local PGD level page.
  */
+#ifdef CONFIG_X86_5LEVEL
+void sync_global_pgds(unsigned long start, unsigned long end, int removed)
+{
+        unsigned long address;
+
+       for (address = start; address <= end && address >= start;
+                       address += PGDIR_SIZE) {
+                const pgd_t *pgd_ref = pgd_offset_k(address);
+                struct page *page;
+
+                /*
+                 * When it is called after memory hot remove, pgd_none()
+                 * returns true. In this case (removed == 1), we must clear
+                 * the PGD entries in the local PGD level page.
+                 */
+                if (pgd_none(*pgd_ref) && !removed)
+                        continue;