mm, x86: add support for PUD-sized transparent hugepages

The current transparent hugepage code only supports PMDs.  This patch adds
support for transparent use of PUDs with DAX.  It does not include support
for anonymous pages.  x86 support code also added.

Most of this patch simply parallels the work that was done for huge PMDs.
The only major difference is how the new ->pud_entry method in mm_walk
works.  The ->pmd_entry method replaces the ->pte_entry method, whereas
the ->pud_entry method works along with either ->pmd_entry or ->pte_entry.
The pagewalk code takes care of locking the PUD before calling
->pud_walk, so handlers do not need to worry whether the PUD is stable.

Link: http://lkml.kernel.org/r/148545059381.17912.8602162635537598445.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jan Kara <jack@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Nilesh Choudhury <nilesh.choudhury@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 19 insertions, 1 deletions

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 207244489a68..03761577ae86 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -78,14 +78,32 @@ static int walk_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end,
 
 	pud = pud_offset(pgd, addr);
 	do {
+ again:
 		next = pud_addr_end(addr, end);
-		if (pud_none_or_clear_bad(pud)) {
+		if (pud_none(*pud) || !walk->vma) {
 			if (walk->pte_hole)
 				err = walk->pte_hole(addr, next, walk);
 			if (err)
 				break;
 			continue;
 		}
+
+		if (walk->pud_entry) {
+			spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
+
+			if (ptl) {
+				err = walk->pud_entry(pud, addr, next, walk);
+				spin_unlock(ptl);
+				if (err)
+					break;
+				continue;
+			}
+		}
+
+		split_huge_pud(walk->vma, pud, addr);
+		if (pud_none(*pud))
+			goto again;
+
 		if (walk->pmd_entry || walk->pte_entry)
 			err = walk_pmd_range(pud, addr, next, walk);
 		if (err)