From e5ad581c7f1c32d309ae4e895eea0cd1a3d9f363 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd@google.com>
Date: Thu, 8 Jun 2023 18:20:04 -0700
Subject: [PATCH] mm/vmwgfx: simplify pmd & pud mapping dirty helpers
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wp_clean_pmd_entry() need not check pmd_trans_unstable() or pmd_none(),
wp_clean_pud_entry() need not check pud_trans_unstable() or pud_none():
it's just the ACTION_CONTINUE when trans_huge or devmap that's needed to
prevent splitting, and we're hoping to remove pmd_trans_unstable().  Is
that PUD #ifdef necessary?  Maybe some configs are missing a stub.

Link: https://lkml.kernel.org/r/d3379c7-65db-26d3-1764-8e866490925f@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/mapping_dirty_helpers.c | 34 +++++++++-------------------------
 1 file changed, 9 insertions(+), 25 deletions(-)

diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c
index e1eb33f..87b4bee 100644
--- a/mm/mapping_dirty_helpers.c
+++ b/mm/mapping_dirty_helpers.c
@@ -128,19 +128,11 @@ static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 {
 	pmd_t pmdval = pmdp_get_lockless(pmd);
 
-	if (!pmd_trans_unstable(&pmdval))
-		return 0;
-
-	if (pmd_none(pmdval)) {
-		walk->action = ACTION_AGAIN;
-		return 0;
-	}
-
-	/* Huge pmd, present or migrated */
-	walk->action = ACTION_CONTINUE;
-	if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
+	/* Do not split a huge pmd, present or migrated */
+	if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval)) {
 		WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
-
+		walk->action = ACTION_CONTINUE;
+	}
 	return 0;
 }
 
@@ -156,23 +148,15 @@ static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
 			      struct mm_walk *walk)
 {
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 	pud_t pudval = READ_ONCE(*pud);
 
-	if (!pud_trans_unstable(&pudval))
-		return 0;
-
-	if (pud_none(pudval)) {
-		walk->action = ACTION_AGAIN;
-		return 0;
-	}
-
-#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
-	/* Huge pud */
-	walk->action = ACTION_CONTINUE;
-	if (pud_trans_huge(pudval) || pud_devmap(pudval))
+	/* Do not split a huge pud */
+	if (pud_trans_huge(pudval) || pud_devmap(pudval)) {
 		WARN_ON(pud_write(pudval) || pud_dirty(pudval));
+		walk->action = ACTION_CONTINUE;
+	}
 #endif
-
 	return 0;
 }
 
-- 
2.7.4