From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 35B6A34BA50; Mon, 29 Sep 2025 04:44:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759121065; cv=none; b=jVQ53MjRKRisBbEQSFSjD0uLoPQUGEC9B7G0jnGeBc04B9DT+F9onR0VTmx/Lgo9aN9QU9dTgKkQQlsQBvHR6dwqQ7ZIGC7UP0/9GkaVS7wvn3CJdGd25xFEXEnjQUuWFGMnGMl/0EWR5QqFiJUrilU5z3UA2hc3vzM0HceBUgc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759121065; c=relaxed/simple; bh=3ZXXQLU0QKxHT4JrTnlId2Pc9wqCYziE2zGHji+O02Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LCZeRvbGZ3hZ5SsVIfhflYrYpkB74460X7xZEQcwMOwI2A7WEkIgwBDZYzzX+DfHC8SYu8vJnNk9w/GJsTnIAFoRWuozsBZxP7a5bMxNYlJ95HP+ZPkvJhpgFkyi06bQg/2UmeFRqucf/PTU00pWWoKdKgjUlKNL2XbHhgbQpHk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2AA0C150C; Sun, 28 Sep 2025 21:44:14 -0700 (PDT) Received: from [10.164.18.53] (MacBook-Pro.blr.arm.com [10.164.18.53]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 37BD83F66E; Sun, 28 Sep 2025 21:44:13 -0700 (PDT) Message-ID: <2065263d-a2c0-437e-a096-695c6d17f97a@arm.com> Date: Mon, 29 Sep 2025 10:14:10 +0530 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/rmap: fix soft-dirty bit loss when remapping zero-filled mTHP subpage to shared zeropage To: Lance Yang , 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, 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 References: <20250928044855.76359-1-lance.yang@linux.dev> Content-Language: en-US From: Dev Jain In-Reply-To: <20250928044855.76359-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 28/09/25 10:18 am, Lance Yang wrote: > 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)); I think this should work. You can pass old_pte = ptep_get(pvmw->pte) to this function to avoid calling ptep_get() multiple times.