From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 462C226FDB2 for ; Mon, 29 Sep 2025 10:15:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759140957; cv=none; b=EpaWPGSC7efIURXBtEZCTDcU97HOnQGqJeDuYAmIlmg4EBy5jG5v50C7DbwbkoIS3q+0IZtunHfUjxIPPebRy9t+aJX27MmNfQcvrpAdSzGo7TciyaV9SYXFGJIAPlEiLmaMcOyebHeT0WH7Qvg0sFyO7Y86SWB0RrDnkiksHoY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759140957; c=relaxed/simple; bh=OlJqGE1Z97dkVyrN0caTtErA3Xa9MnJBfPFMdEyvW9w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oX2i4QpqNe5hmTvLFxvI/56cXrWQfBISQaPML+vFY6aJkiw2JVMyNwYfnV/KrYsN1uk9D8ozIVEP8Z9hUOU5bSvDZneWPtWBpwypmG2uo8O2uxR4bvzdothJtKhwW5FiKr+NJRXqfvgPgriR+if+FupIaim1jVAnzK/hPp5xxDg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=gzO39fAC; arc=none smtp.client-ip=95.215.58.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="gzO39fAC" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1759140943; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0lDTfGg/6Uyqwfi6NmuvIilfdfFny0fXjAuu0Bjee84=; b=gzO39fACECb42zPXJwdyj6Jv27mioHJsXOtNOgcfJ+jWFO9VImd3+gUNkHtBP/obtV3B7B pFJMjkkPJqkUu67chDrlvcIkKpsNMrW9Bn08O92QVgLhNIqIFhRQ4VYEvvxjJgrjLaQWri YMHMpUqryT0WsiiYzr+1JRdaCwrF8G8= Date: Mon, 29 Sep 2025 18:15:29 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 1/1] mm/rmap: fix soft-dirty bit loss when remapping zero-filled mTHP subpage to shared zeropage Content-Language: en-US To: Dev Jain 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, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, david@redhat.com References: <20250928044855.76359-1-lance.yang@linux.dev> <2065263d-a2c0-437e-a096-695c6d17f97a@arm.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <2065263d-a2c0-437e-a096-695c6d17f97a@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2025/9/29 12:44, Dev Jain wrote: > > 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. Good catch! Will do in v2, thanks.