From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (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 D044A26B2AD; Wed, 29 Apr 2026 13:47:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.156.1 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777470449; cv=none; b=e5FjjanmsrenbIYTfiMnNVXJLTRjtgJV9KvEU8kHdeiGLP+vLxZIUy+8ZZl7+jAjsonRGK7cB/oFmymgfemxLHOrhYtTBAfGS+ACusuUBMoO9TXCZcWF/AHW8HE31gvnIk9yf6x4lD9FhuOHMLNIaTK/b70Yy+DPTT0QJMSUgi0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777470449; c=relaxed/simple; bh=JqGfCjKAkCjTRBfbPVov/coEyIxtNwMAwSwv+Nk9+2g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YmRgo7i7CgAtSvmWicJrZQvbH3Ba+QIVk7dRcPqRGhXCQ/MeTt3Lawaih7dMSjP+pM6c1/etmqR9894IoK5GDQ/E7Oak9zkp6yPDFfzUrMFISj3QcfL8IzdDTqConkaIw+OEB6dnuAeG4YKL2kv7u2DSEVgF7w7v8cg0rCEL5to= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=CNZ694g+; arc=none smtp.client-ip=148.163.156.1 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="CNZ694g+" Received: from pps.filterd (m0356517.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 63T4ZTsr1694171; Wed, 29 Apr 2026 13:47:21 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-type:date:from:in-reply-to:message-id:mime-version :references:subject:to; s=pp1; bh=rOMQ6tII+w8eM+1uscKo4u6a8wS/+Z JZoe0f7koUOJM=; b=CNZ694g+lx5Ew32q5FKyxrU3a3d0qvQt4rV+Ypd6d1X+q4 s2HHxrzNN0odYWHZreznFG0prK/1o2U2F0rxQudEGlQvvW7nn9l2TGUK11ASI9C7 YgZXkJ0gQXDEIT+TKhrjpFyhqqZmnOzPuxv1sAqgtQh06J6BlUZ4uJ3h1jD/hsGc e5zlCAdXO0aCAZluv5yZRjz2fpVPWdOgjIxJSRYKwUZuiq6r4tmqla7oAJdNpEaW Xjst4GMxaBcKtG0AZVXQJIo0zUdg5uzj3fxT1YKx1DKOi4BlcYxHX9InLRHptWnt KTc1cMI/MjetQ9OOPfq05+PPyk6IhQsPbdikwhwA== Received: from ppma12.dal12v.mail.ibm.com (dc.9e.1632.ip4.static.sl-reverse.com [50.22.158.220]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4drnb5arpb-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 29 Apr 2026 13:47:21 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 63TDdIjW030500; Wed, 29 Apr 2026 13:47:20 GMT Received: from smtprelay05.fra02v.mail.ibm.com ([9.218.2.225]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 4ds7xqemu7-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 29 Apr 2026 13:47:20 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 63TDlGYk35324172 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 29 Apr 2026 13:47:17 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DB56E20043; Wed, 29 Apr 2026 13:47:16 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id ABAC720040; Wed, 29 Apr 2026 13:47:16 +0000 (GMT) Received: from li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com (unknown [9.52.215.75]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTPS; Wed, 29 Apr 2026 13:47:16 +0000 (GMT) Date: Wed, 29 Apr 2026 15:47:15 +0200 From: Alexander Gordeev To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Lorenzo Stoakes , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_vma_mapped_walk: add missing pgtable entry accessors Message-ID: References: <20260427052000.196402-1-agordeev@linux.ibm.com> <69c4c12c-7cdc-4a17-9eb7-6fb1a61f9834@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69c4c12c-7cdc-4a17-9eb7-6fb1a61f9834@kernel.org> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=AqDeGu9P c=1 sm=1 tr=0 ts=69f20be9 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=kj9zAlcOel0A:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=j5aMtUXh0naQkGdsk6gA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDI5MDE0MCBTYWx0ZWRfXxTSLyxKf6Pf8 KNJ4rpP3Syi3oag+YKwk2Awq0cKPIrlvQRSHdzQTbeh8Q7+KoS2b+6HBEHa5H7lnQvExaY0Nrx0 uevRDFwpfxCIba8sG0GOWAgPBMRx6xMSD0lNsaf6BIrg9H/45oNt82xpQrzFf8KFTPtEP1AnK/V sCRL092IemCs/GOOUIP0XsCiubusBVz5L6NAK1+dAgkWAC7uPB/O8tsPT4IBhF+ugi63H97hCf1 IirZAWGGdvH7RW0veIlzaEdq0gN8CrRCNSu/FWoKPkXkfcatIQ3jif0uY4pixVvyZcB+5eha7e/ TVh3KwJiQ4mccDPASbBftAkKi44/MGwjNOrxJpITyVqjz/SJ4QTejhmU0RbU/cZ3YeKRNd7GW3I kRdRVtuMV+4zq5820dckDRlgBJf7IGzgLmgeewbRj4rGfSNNKZXmtPJuXC45/1uPEkQqR/3m2dw 23HZBNYyFad76jUnRAA== X-Proofpoint-GUID: yrv26ZzoKgHOt5QRWgP9HHSlaVzGQMv6 X-Proofpoint-ORIG-GUID: yrv26ZzoKgHOt5QRWgP9HHSlaVzGQMv6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-28_05,2026-04-28_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 phishscore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 spamscore=0 bulkscore=0 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2604290140 On Mon, Apr 27, 2026 at 11:02:50AM +0200, David Hildenbrand (Arm) wrote: > On 4/27/26 07:20, Alexander Gordeev wrote: > > Convert pgtable direct entry dereferences to the corresponding > > pXdp_get() accessors. Use ptep_get_lockless() variant for PTE > > reads when no lock is taken. > > > > Signed-off-by: Alexander Gordeev > > --- > > mm/page_vma_mapped.c | 12 ++++++------ > > 1 file changed, 6 insertions(+), 6 deletions(-) > > > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > > index b38a1d00c971..a4520bb10d2a 100644 > > --- a/mm/page_vma_mapped.c > > +++ b/mm/page_vma_mapped.c > > @@ -41,7 +41,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp, > > if (!pvmw->pte) > > return false; > > > > - ptent = ptep_get(pvmw->pte); > > + ptent = ptep_get_lockless(pvmw->pte); (*) > > if (pte_none(ptent)) { > > return false; > > @@ -219,17 +219,17 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > > restart: > > do { > > pgd = pgd_offset(mm, pvmw->address); > > - if (!pgd_present(*pgd)) { > > + if (!pgd_present(pgdp_get(pgd))) { > > step_forward(pvmw, PGDIR_SIZE); > > continue; > > } > > p4d = p4d_offset(pgd, pvmw->address); > > - if (!p4d_present(*p4d)) { > > + if (!p4d_present(p4dp_get(p4d))) { > > step_forward(pvmw, P4D_SIZE); > > continue; > > } > > pud = pud_offset(p4d, pvmw->address); > > - if (!pud_present(*pud)) { > > + if (!pud_present(pudp_get(pud))) { > > step_forward(pvmw, PUD_SIZE); > > continue; > > Wasn't there a problem with folded page tables, where we would no longer be able > to optimize out the folded page table accesses? Ok, that is a different topic. I actually tried to resolve the lockless issue(s) in (*) while the direct dereferences just seemed to be relevant to go along (similarly to the GUP patch). But I would rather resend ptep_get() => ptep_get_lockless() fixes for this patch. Would it work? > I thought we discussed ways to resolve that. Let me dig ... > > > -- > Cheers, > > David Thanks!