kaiser: allocate pgd with order 0 when pti=off

The 4.9.77 version of "x86/pti/efi: broken conversion from efi to kernel
page table" looked nicer than the 4.4.112 version, but was suboptimal on
machines booted with "pti=off" (or on AMD machines): it allocated pgd
with an order 1 page whatever the setting of kaiser_enabled.

Fix that by moving the definition of PGD_ALLOCATION_ORDER from
asm/pgalloc.h to asm/pgtable.h, which already defines kaiser_enabled.

Fixes: 1b92c48a ("x86/pti/efi: broken conversion from efi to kernel page table")
Reviewed-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Steven Sistare <steven.sistare@oracle.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/pgalloc.h

@@ -27,17 +27,6 @@ static inline void paravirt_release_pud(unsigned long pfn) {}
  */
 extern gfp_t __userpte_alloc_gfp;
 
-#ifdef CONFIG_PAGE_TABLE_ISOLATION
-/*
- * Instead of one PGD, we acquire two PGDs.  Being order-1, it is
- * both 8k in size and 8k-aligned.  That lets us just flip bit 12
- * in a pointer to swap between the two 4k halves.
- */
-#define PGD_ALLOCATION_ORDER 1
-#else
-#define PGD_ALLOCATION_ORDER 0
-#endif
-
 /*
  * Allocate and free page tables.
  */

arch/x86/include/asm/pgtable.h

@@ -20,9 +20,15 @@
 
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
 extern int kaiser_enabled;
+/*
+ * Instead of one PGD, we acquire two PGDs.  Being order-1, it is
+ * both 8k in size and 8k-aligned.  That lets us just flip bit 12
+ * in a pointer to swap between the two 4k halves.
+ */
 #else
 #define kaiser_enabled 0
 #endif
+#define PGD_ALLOCATION_ORDER kaiser_enabled
 
 void ptdump_walk_pgd_level(struct seq_file *m, pgd_t *pgd);
 void ptdump_walk_pgd_level_checkwx(void);