[RFC, PATCHv1 01/28] asm-generic: introduce 5level-fixup.h

[Kirill A. Shutemov]

We are going to switch core MM to 5-level paging abstraction.

This is preparation step which adds <asm-generic/5level-fixup.h>
As with 4level-fixup.h, the new header allows quickly make all
architectures compatible with 5-level paging in core MM.

In long run we would like to switch architectures to properly folded p4d
level by using <asm-generic/pgtable-nop4d.h>, but it requires more
changes to arch-specific code.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 include/asm-generic/4level-fixup.h |  3 ++-
 include/asm-generic/5level-fixup.h | 41 ++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h                 |  3 +++
 3 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 include/asm-generic/5level-fixup.h

diff --git a/include/asm-generic/4level-fixup.h b/include/asm-generic/4level-fixup.h
index 5bdab6bffd23..928fd66b1271 100644
--- a/include/asm-generic/4level-fixup.h
+++ b/include/asm-generic/4level-fixup.h
@@ -15,7 +15,6 @@
 	((unlikely(pgd_none(*(pud))) && __pmd_alloc(mm, pud, address))? \
  		NULL: pmd_offset(pud, address))
 
-#define pud_alloc(mm, pgd, address)	(pgd)
 #define pud_offset(pgd, start)		(pgd)
 #define pud_none(pud)			0
 #define pud_bad(pud)			0
@@ -35,4 +34,6 @@
 #undef  pud_addr_end
 #define pud_addr_end(addr, end)		(end)
 
+#include <asm-generic/5level-fixup.h>
+
 #endif
diff --git a/include/asm-generic/5level-fixup.h b/include/asm-generic/5level-fixup.h
new file mode 100644
index 000000000000..02a71804d9fa
--- /dev/null
+++ b/include/asm-generic/5level-fixup.h
@@ -0,0 +1,41 @@
+#ifndef _5LEVEL_FIXUP_H
+#define _5LEVEL_FIXUP_H
+
+#define __ARCH_HAS_5LEVEL_HACK
+#define __PAGETABLE_P4D_FOLDED
+
+#define P4D_SHIFT			PGDIR_SHIFT
+#define P4D_SIZE			PGDIR_SIZE
+#define P4D_MASK			PGDIR_MASK
+#define PTRS_PER_P4D			1
+
+#define p4d_t				pgd_t
+
+#define pud_alloc(mm, p4d, address) \
+	((unlikely(pgd_none(*(p4d))) && __pud_alloc(mm, p4d, address))? \
+		NULL: pud_offset(p4d, address))
+
+#define p4d_alloc(mm, pgd, address)	(pgd)
+#define p4d_offset(pgd, start)		(pgd)
+#define p4d_none(p4d)			0
+#define p4d_bad(p4d)			0
+#define p4d_present(p4d)		1
+#define p4d_ERROR(p4d)			do { } while (0)
+#define p4d_clear(p4d)			pgd_clear(p4d)
+#define p4d_val(p4d)			pgd_val(p4d)
+#define p4d_populate(mm, p4d, pud)	pgd_populate(mm, p4d, pud)
+#define p4d_page(p4d)			pgd_page(p4d)
+#define p4d_page_vaddr(p4d)		pgd_page_vaddr(p4d)
+
+#define __p4d(x)			__pgd(x)
+#define set_p4d(p4dp, p4d)		set_pgd(p4dp, p4d)
+
+#undef p4d_free_tlb
+#define p4d_free_tlb(tlb, x, addr)	do { } while (0)
+#define p4d_free(mm, x)			do { } while (0)
+#define __p4d_free_tlb(tlb, x, addr)	do { } while (0)
+
+#undef  p4d_addr_end
+#define p4d_addr_end(addr, end)		(end)
+
+#endif
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ef815b9cd426..9a4dfd7c3515 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1600,11 +1600,14 @@ int __pte_alloc_kernel(pmd_t *pmd, unsigned long address);
  * Remove it when 4level-fixup.h has been removed.
  */
 #if defined(CONFIG_MMU) && !defined(__ARCH_HAS_4LEVEL_HACK)
+
+#ifndef __ARCH_HAS_5LEVEL_HACK
 static inline pud_t *pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
 {
 	return (unlikely(pgd_none(*pgd)) && __pud_alloc(mm, pgd, address))?
 		NULL: pud_offset(pgd, address);
 }
+#endif /* !__ARCH_HAS_5LEVEL_HACK */
 
 static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 {
-- 
2.10.2