From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 21064CAC5B0 for ; Mon, 29 Sep 2025 04:44:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 09DEE8E0003; Mon, 29 Sep 2025 00:44:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0766D8E0002; Mon, 29 Sep 2025 00:44:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EF5458E0003; Mon, 29 Sep 2025 00:44:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id DC18F8E0002 for ; Mon, 29 Sep 2025 00:44:25 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 4FA3B84724 for ; Mon, 29 Sep 2025 04:44:25 +0000 (UTC) X-FDA: 83941046490.30.F1C2024 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf09.hostedemail.com (Postfix) with ESMTP id 3D4E6140002 for ; Mon, 29 Sep 2025 04:44:23 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=none; spf=pass (imf09.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1759121063; h=from:from:sender: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=9km3TTOsFYsfDyai+3IcmTkqC5YN4/2Z0p8DX5JCU2k=; b=aIby1RtztHPc55CPan87IOqJrjEvAkHcjlZCPdD5Czu6bdK6DoDLcG375d2oieANZoax2k N9tEq5O094hbfDUB/FV5Xcb3W/pjJwKVbQ6s4KioSInQ45yvXmgqnw23Rpjsvnf5gtdu2B EFoMY1ywtUoKbE4gCVOUCBD7Zivl8yw= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1759121063; a=rsa-sha256; cv=none; b=tN3vky4993q8dH4mhGewvNIcpgq+6msLqh4QuKs3DZ+b0eyMCPSGLBxilyObWYFUktXFNv KEr7wzFDxAbuo6TZqBeZMW9qNDMLw+KjBRD79E/1NFfEUHIVt3UcsOzQViSY1TbfpEE5c0 04Y/FLH0VcKmcrJC7LjHxIn1eES1UHk= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=none; spf=pass (imf09.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=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 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 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3D4E6140002 X-Stat-Signature: mk86tj5fdjsx56aikh75owrfjooo4w4k X-Rspam-User: X-HE-Tag: 1759121063-747084 X-HE-Meta: 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 Fygs1LeD tmhugu2XSy5TagLj5+IxSvmNZIVguWpu3UE4UD4rZpmw6p+6QnOnkGu68HLewq3NBlB4k8EMwqgoexQuCIMqVauMAobXQy1LhnAYIIix8GePIZ0tclkD/Dvzrs+yK9mkyXzGod0ImwwDVjeFiorVsiX0qJ7cAYX2fUiCX7irK+XpQXj8l7jkrywwgA48ElyIzUjpy06RWrxe7DfrxU4gUhyuNkIZC5X2gTmoIZIiHiQ1hb/E= 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: 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.