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

[yulei . kernel]

From: Yulei Zhang <yuleixzh...@tencent.com>

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 <sagazc...@tencent.com>
Signed-off-by: Yulei Zhang <yuleixzh...@tencent.com>
---
 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