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Sat, 27 Sep 2025 21:49:20 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, ryan.roberts@arm.com, dev.jain@arm.com, npache@redhat.com, riel@surriel.com, Liam.Howlett@oracle.com, vbabka@suse.cz, harry.yoo@oracle.com, jannh@google.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, usamaarif642@gmail.com, yuzhao@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ioworker0@gmail.com, stable@vger.kernel.org, Lance Yang Subject: [PATCH 1/1] mm/rmap: fix soft-dirty bit loss when remapping zero-filled mTHP subpage to shared zeropage Date: Sun, 28 Sep 2025 12:48:55 +0800 Message-ID: <20250928044855.76359-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 877B3100009 X-Stat-Signature: ikidbi7sy191xjdqxq4ginh749d89qse X-Rspam-User: X-HE-Tag: 1759034962-697206 X-HE-Meta: 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 gGPWM+7H 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Lance Yang When splitting an mTHP and replacing a zero-filled subpage with the shared zeropage, try_to_map_unused_to_zeropage() currently drops the soft-dirty bit. For userspace tools like CRIU, which rely on the soft-dirty mechanism for incremental snapshots, losing this bit means modified pages are missed, leading to inconsistent memory state after restore. Preserve the soft-dirty bit from the old PTE when creating the zeropage mapping to ensure modified pages are correctly tracked. Cc: Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") Signed-off-by: Lance Yang --- mm/migrate.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/migrate.c b/mm/migrate.c index ce83c2c3c287..bf364ba07a3f 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -322,6 +322,10 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address), pvmw->vma->vm_page_prot)); + + if (pte_swp_soft_dirty(ptep_get(pvmw->pte))) + newpte = pte_mksoft_dirty(newpte); + set_pte_at(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, newpte); dec_mm_counter(pvmw->vma->vm_mm, mm_counter(folio)); -- 2.49.0