linux-kernel - [PATCH] fixup! mm/pagewalk: Check pfnmap for folio_walk

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Message-ID: <20240829202237.2640288-1-peterx@redhat.com>
Date: Thu, 29 Aug 2024 16:22:37 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: peterx@...hat.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jason Gunthorpe <jgg@...dia.com>,
	David Hildenbrand <david@...hat.com>
Subject: [PATCH] fixup! mm/pagewalk: Check pfnmap for folio_walk_start()

Per David's suggestion, remove some stale comment in vm_normal_page_pmd()
as we start to have special bit in pmd too.  Meanwhile move the
pmd_special() check here from folio_walk_start().

Signed-off-by: Peter Xu <peterx@...hat.com>
---

Andrew, would you consider squashing this patch into the commit
"mm/pagewalk: Check pfnmap for folio_walk_start()" in mm-unstable?  This is
so far the only thing I plan to update on the huge pfnmap series, thanks.
---
 mm/memory.c   | 9 ++++-----
 mm/pagewalk.c | 2 +-
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 06b42db8a2db..b95fce7d190f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -672,11 +672,10 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
 {
 	unsigned long pfn = pmd_pfn(pmd);
 
-	/*
-	 * There is no pmd_special() but there may be special pmds, e.g.
-	 * in a direct-access (dax) mapping, so let's just replicate the
-	 * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here.
-	 */
+	/* Currently it's only used for huge pfnmaps */
+	if (unlikely(pmd_special(pmd)))
+		return NULL;
+
 	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
 		if (vma->vm_flags & VM_MIXEDMAP) {
 			if (!pfn_valid(pfn))
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 12be5222d70e..461ea3bbd8d9 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -783,7 +783,7 @@ struct folio *folio_walk_start(struct folio_walk *fw,
 		fw->pmdp = pmdp;
 		fw->pmd = pmd;
 
-		if (pmd_none(pmd) || pmd_special(pmd)) {
+		if (pmd_none(pmd)) {
 			spin_unlock(ptl);
 			goto not_found;
 		} else if (!pmd_leaf(pmd)) {
-- 
2.45.0