Re: [PATCHv2 02/29] asm-generic: introduce 5level-fixup.h

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On 12/27/2016 02:53 AM, Kirill A. Shutemov wrote:
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)

This...

 #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>

... plus this...

+
 #endif
diff --git a/include/asm-generic/5level-fixup.h b/include/asm-generic/5level-fixup.h
new file mode 100644
index 000000000000..b5ca82dc4175
--- /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))

... and this, makes me wonder if that broke pud_alloc() for architectures that use the 4level-fixup.h. Don't those need to continue having pud_alloc() as (pgd)?

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