x86/mm: Make PGDIR_SHIFT and PTRS_PER_P4D variable

For boot-time switching between 4- and 5-level paging we need to be able
to fold p4d page table level at runtime. It requires variable
PGDIR_SHIFT and PTRS_PER_P4D.

The change doesn't affect the kernel image size much:

   text	   data	    bss	    dec	    hex	filename
8628091	4734304	1368064	14730459	 e0c4db	vmlinux.before
8628393	4734340	1368064	14730797	 e0c62d	vmlinux.after

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180214111656.88514-7-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/dump_pagetables.c

@@ -428,14 +428,15 @@ static void walk_pud_level(struct seq_file *m, struct pg_state *st, p4d_t addr,
 #define p4d_none(a)  pud_none(__pud(p4d_val(a)))
 #endif
 
-#if PTRS_PER_P4D > 1
-
 static void walk_p4d_level(struct seq_file *m, struct pg_state *st, pgd_t addr, unsigned long P)
 {
 	int i;
 	p4d_t *start, *p4d_start;
 	pgprotval_t prot;
 
+	if (PTRS_PER_P4D == 1)
+		return walk_pud_level(m, st, __p4d(pgd_val(addr)), P);
+
 	p4d_start = start = (p4d_t *)pgd_page_vaddr(addr);
 
 	for (i = 0; i < PTRS_PER_P4D; i++) {
@@ -455,11 +456,8 @@ static void walk_p4d_level(struct seq_file *m, struct pg_state *st, pgd_t addr,
 	}
 }
 
-#else
-#define walk_p4d_level(m,s,a,p) walk_pud_level(m,s,__p4d(pgd_val(a)),p)
-#define pgd_large(a) p4d_large(__p4d(pgd_val(a)))
-#define pgd_none(a)  p4d_none(__p4d(pgd_val(a)))
-#endif
+#define pgd_large(a) (pgtable_l5_enabled ? pgd_large(a) : p4d_large(__p4d(pgd_val(a))))
+#define pgd_none(a)  (pgtable_l5_enabled ? pgd_none(a) : p4d_none(__p4d(pgd_val(a))))
 
 static inline bool is_hypervisor_range(int idx)
 {

arch/x86/mm/init_64.c

@@ -143,7 +143,7 @@ void sync_global_pgds(unsigned long start, unsigned long end)
 		 * With folded p4d, pgd_none() is always false, we need to
 		 * handle synchonization on p4d level.
 		 */
-		BUILD_BUG_ON(pgd_none(*pgd_ref));
+		MAYBE_BUILD_BUG_ON(pgd_none(*pgd_ref));
 		p4d_ref = p4d_offset(pgd_ref, addr);
 
 		if (p4d_none(*p4d_ref))

arch/x86/mm/kasan_init_64.c

@@ -19,7 +19,7 @@
 
 extern struct range pfn_mapped[E820_MAX_ENTRIES];
 
-static p4d_t tmp_p4d_table[PTRS_PER_P4D] __initdata __aligned(PAGE_SIZE);
+static p4d_t tmp_p4d_table[MAX_PTRS_PER_P4D] __initdata __aligned(PAGE_SIZE);
 
 static __init void *early_alloc(size_t size, int nid, bool panic)
 {