[PATCH] tmp

[David Hildenbrand (Arm)]

Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
---
 mm/pagewalk.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index cb358558807c..779f6fa00ab7 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -96,6 +96,7 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
 			  struct mm_walk *walk)
 {
+	pud_t pudval = pudp_get(pud);
 	pmd_t *pmd;
 	unsigned long next;
 	const struct mm_walk_ops *ops = walk->ops;
@@ -104,6 +105,18 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
 	int err = 0;
 	int depth = real_depth(3);
 
+	/*
+	 * For PTE handling, pte_offset_map_lock() takes care of checking
+	 * whether there actually is a page table. But it also has to be
+	 * very careful about concurrent page table reclaim. If we spot a PMD
+	 * table, it cannot go away, so we can just walk it. However, if we find
+	 * something else, we have to retry.
+	 */
+	if (!pud_present(pudval) || pud_leaf(pudval)) {
+		walk->action = ACTION_AGAIN;
+		return 0;
+	}
+
 	pmd = pmd_offset(pud, addr);
 	do {
 again:
@@ -176,7 +189,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
 
 	pud = pud_offset(p4d, addr);
 	do {
- again:
+again:
 		next = pud_addr_end(addr, end);
 		if (pud_none(*pud)) {
 			if (has_install)
@@ -217,12 +230,13 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
 		else if (pud_leaf(*pud) || !pud_present(*pud))
 			continue; /* Nothing to do. */
 
-		if (pud_none(*pud))
-			goto again;
-
 		err = walk_pmd_range(pud, addr, next, walk);
 		if (err)
 			break;
+
+		if (walk->action == ACTION_AGAIN)
+			goto again;
+
 	} while (pud++, addr = next, addr != end);
 
 	return err;
-- 
2.43.0


-- 
Cheers,

David