[RFC V2 19/37] mm: gup_huge_pmd() for dmem huge pmd

[yulei . kernel]

From: Yulei Zhang <yuleixzhang@xxxxxxxxxxx>

Add pmd_special() check in gup_huge_pmd() to support dmem huge pmd.
GUP will return zero if enconter dmem page, and we could handle it
outside GUP routine.

Signed-off-by: Chen Zhuo <sagazchen@xxxxxxxxxxx>
Signed-off-by: Yulei Zhang <yuleixzhang@xxxxxxxxxxx>
---
 mm/gup.c      | 6 +++++-
 mm/pagewalk.c | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index ad1aede..47c8197 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2470,6 +2470,10 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
 		return 0;
 
+	/* Bypass dmem huge pmd. It will be handled in outside routine. */
+	if (pmd_special(orig))
+		return 0;
+
 	if (pmd_devmap(orig)) {
 		if (unlikely(flags & FOLL_LONGTERM))
 			return 0;
@@ -2572,7 +2576,7 @@ static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned lo
 			return 0;
 
 		if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) ||
-			     pmd_devmap(pmd))) {
+			     pmd_devmap(pmd) || pmd_special(pmd))) {
 			/*
 			 * NUMA hinting faults need to be handled in the GUP
 			 * slowpath for accounting purposes and so that they
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index e81640d..e7c4575 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -71,7 +71,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
 	do {
 again:
 		next = pmd_addr_end(addr, end);
-		if (pmd_none(*pmd) || (!walk->vma && !walk->no_vma)) {
+		if (pmd_none(*pmd) || (!walk->vma && !walk->no_vma) || pmd_special(*pmd)) {
 			if (ops->pte_hole)
 				err = ops->pte_hole(addr, next, depth, walk);
 			if (err)
-- 
1.8.3.1