+ mm-ksm-keep-soft-dirty-when-merging-a-page.patch added to mm-unstable branch

+ mm-ksm-keep-soft-dirty-when-merging-a-page.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/ksm: keep soft-dirty when merging a page
has been added to the -mm mm-unstable branch.  Its filename is
     mm-ksm-keep-soft-dirty-when-merging-a-page.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-ksm-keep-soft-dirty-when-merging-a-page.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Samarth Narang <samarth.colleges@gmail.com>
Subject: mm/ksm: keep soft-dirty when merging a page
Date: Wed, 21 Oct 2026 11:21:57 -0700

replace_page() maps the KSM page with a PTE built from scratch, so the
soft-dirty bit of the PTE it replaces is lost.  A page written since
"clear_refs 4" then no longer shows as soft-dirty once it is merged, and a
soft-dirty based dumper treats it as unchanged.

Copy the soft-dirty bit from the original PTE to the new PTE.

Link: https://lore.kernel.org/20261021182157.1873726-1-samarth.colleges@gmail.com
Fixes: 0f8975ec4db2 ("mm: soft-dirty bits for user memory changes tracking")
Signed-off-by: Samarth Narang <samarth.colleges@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Assisted-by: LLM
Cc: David Hildenbrand <david@kernel.org>
Cc: Xu Xin <xu.xin@linux.dev>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: <stable@vger.kernel.org>
---

 mm/ksm.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/ksm.c~mm-ksm-keep-soft-dirty-when-merging-a-page
+++ a/mm/ksm.c
@@ -1463,6 +1463,10 @@ static int replace_page(struct vm_area_s
 		dec_mm_counter(mm, MM_ANONPAGES);
 	}
 
+	/* Preserve soft-dirty when replacing the page. */
+	if (pte_soft_dirty(orig_pte))
+		newpte = pte_mksoft_dirty(newpte);
+
 	flush_cache_page(vma, addr, pte_pfn(ptep_get(ptep)));
 	/*
 	 * No need to notify as we are replacing a read only page with another
_

Patches currently in -mm which might be from samarth.colleges@gmail.com are

mm-ksm-keep-soft-dirty-when-merging-a-page.patch