From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (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 435F147ACC8; Wed, 29 Jul 2026 11:51:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785325920; cv=none; b=L5YchBNK8CvO188zxIUaaWTaNRUFyCQS7mFtXuSGt0JObL/nt+AXNDP5MP74+B7CGGAMLyCn19a8BSxCycLZqpBMevmgTeb9QlIaOhFEZIT328cqPsvOVQbYCjMEvPOEdeN4a0zsR30NoiX6Ig0yUxg2jAAGiThwMPzjc0diwbg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785325920; c=relaxed/simple; bh=ZO5VxVQKFuSsO1hmvDMPvMAMSsW2f8aJh3n5wjdxgXM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VRY24MYAngxQDe9f/YZ91bbywjKWeRmzTEgFazcfWAH4q+WyplzDglvpYbYrCjKqpmLcl86IitTxUn78rC/QbEk952i8zkBCl7pT6dwK+wqHEwTiX7KcPrk1rDElDove4Vo/d3+BpswmyzK0xR0hS6g/IWIrPLvKuj/UL4eJtd8= 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=szQcOSDi; arc=none smtp.client-ip=148.163.158.5 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="szQcOSDi" Received: from pps.filterd (m0360072.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 66TBI9Rp4077212; Wed, 29 Jul 2026 11:44:24 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=V/Gc5b6Kanb7gJZ6LuCqbHgIfbcHiL UID8lNDkmdkBk=; b=szQcOSDicNI1Fn0H7xW/dMFikndq57iS0AEADbTHurKpEJ rd11kf+v/K4k3OaPX2DwPIScg0o+GL2hoyX8zqoHbYXdT0lSMDdG2vUgrwbDAvmS GAkXnnb9JBVhPcfVoGJY1DSA/6xfq5K9WNKizak7KaKjt/Dc2/+JfX8nFAp5plmo u0a4AxRt+xdBtl/2NsNsMcf1ZDG6Qjqw5xDVM5TyjGqcQsLSIksGXsQcQlaj/plp JuFSfwIB5TVS6mlK0Oz0clytfcFfXgk9OoMJ2+E1DEvmvdCalj6j+Xxe5b2oQCY7 x4RvKe8ts/TDSPuLOoLmIyWAmZfVZWIqbDTv23XQ== Received: from ppma13.dal12v.mail.ibm.com (dd.9e.1632.ip4.static.sl-reverse.com [50.22.158.221]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4fmuwd1p2u-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 29 Jul 2026 11:44:23 +0000 (GMT) Received: from pps.filterd (ppma13.dal12v.mail.ibm.com [127.0.0.1]) by ppma13.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 66TBfHNq029357; Wed, 29 Jul 2026 11:44:22 GMT Received: from smtprelay03.fra02v.mail.ibm.com ([9.218.2.224]) by ppma13.dal12v.mail.ibm.com (PPS) with ESMTPS id 4fn9pgeadd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 29 Jul 2026 11:44:22 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (smtpav04.fra02v.mail.ibm.com [10.20.54.103]) by smtprelay03.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 66TBiKQM31916432 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 29 Jul 2026 11:44:20 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 992952004B; Wed, 29 Jul 2026 11:44:20 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 288E620043; Wed, 29 Jul 2026 11:44:19 +0000 (GMT) Received: from li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com (unknown [9.224.92.206]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTPS; Wed, 29 Jul 2026 11:44:19 +0000 (GMT) Date: Wed, 29 Jul 2026 13:44:17 +0200 From: Alexander Gordeev To: "David Hildenbrand (Arm)" Cc: Muhammad Usama Anjum , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter , Dimitri Sivanich , Arnd Bergmann , Greg Kroah-Hartman , "James E.J. Bottomley" , Helge Deller , Juergen Gross , Stefano Stabellini , Muchun Song , Oscar Salvador , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Andrey Ryabinin , Pasha Tatashin , Chris Li , Kairui Song , Uladzislau Rezki , Steven Rostedt , Masami Hiramatsu , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , SJ Park , "Matthew Wilcox (Oracle)" , Jan Kara , Jason Gunthorpe , Leon Romanovsky , Miaohe Lin , Dennis Zhou , Tejun Heo , Christoph Lameter , Mike Rapoport , Johannes Weiner , ziy@nvidia.com, pfalcato@suse.de, ryan.roberts@arm.com, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-parisc@vger.kernel.org, xen-devel@lists.xenproject.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, kasan-dev@googlegroups.com, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, damon@lists.linux.dev Subject: Re: [PATCH RFC 00/11] mm: distinguish PTE table storage from PTE values Message-ID: References: <20260727164715.2866609-1-usama.anjum@arm.com> <2c19247e-bee6-45f4-a353-2fcc60db26e6@kernel.org> <7813b5fe-e767-442c-a356-afc1a5c567ad-agordeev@linux.ibm.com> <6db0a8c0-b500-4364-be3d-d3a537c61258@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: <6db0a8c0-b500-4364-be3d-d3a537c61258@kernel.org> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Dax4K8SnTqgr3j-xLBjPIG8yJ9gcxvKF X-Proofpoint-Spam-Info: AW1haW4tMjYwNzI5MDA5MyBTYWx0ZWRfX/ftZ3NJRCmkt ZT14DTCChPW4KALpaDbSLe6kNr0LuWq5PiRiSqf5YTIEutfQ2Tac4sdllF74vXnFZSICYrQE0fL ZL/O65SEZjU3i6ZYCyIL5FE+JISdSFU= X-Authority-Analysis: v=2.4 cv=E/z9Y6dl c=1 sm=1 tr=0 ts=6a69e797 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=yGtF1kJb5LocEaEl6I8A:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzI5MDA5MyBTYWx0ZWRfX/jm6YIwwiR1F lZXlePH3tA598H7Fb31vSIvPJoutJ+iSssAlIclxpQnCFqgsl/QXciOAhzwZ7FFazWWtvRVdlZ9 TvRnRR/LIbBRyOBs37OfIHHcuSChvKVhl07RqZv9bpaqy+fPsLibBtb0+CX8Q1amoqeREdzT7LS 45c/SPprx12OPqL4uwkj2S+LtICeW20WUFSc3OlbdqoEpxGRA12dmOFjaryENCnKW/xK1Jay/U1 kC8ReZf28BJ12s4AmwDEQcWLd+44QFBJkS+P1wHLIwJa5nPrgSvB7j/BZoiN3neZKSKOtDNSj09 Q6tFnfgRJpTk6CRkd5peVrkT93tDejNz3zvCXWL/dWWwVW8rI18kBZ3iQaIoQ6o8M4YCglsfenJ wdrKMTl/qwP8vRTkJCoONCRiVYcB8Qwu+P574F7wJpa5ktjFD5+6hw8BDY0mBPrkdR2pGPZzU/d eAJCrvqHF5YRoCZPBfw== X-Proofpoint-GUID: Dax4K8SnTqgr3j-xLBjPIG8yJ9gcxvKF X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-29_04,2026-07-28_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 spamscore=0 clxscore=1015 phishscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607290093 On Wed, Jul 29, 2026 at 01:05:35PM +0200, David Hildenbrand (Arm) wrote: > On 7/29/26 12:13, Alexander Gordeev wrote: > > On Tue, Jul 28, 2026 at 09:26:06PM +0200, David Hildenbrand (Arm) wrote: > >>> The generic definition aliases hw_pte_t to pte_t, so this series preserves > >>> the representation and behaviour of every architecture. ptep_get() keeps > >>> its existing READ_ONCE() semantics and converts the stored element through > >>> __pte_from_hw(). An architecture can later define a distinct hw_pte_t and > >>> convert its PTE interfaces to make the distinction compiler-enforced. > >>> Architecture PTE implementations and most architecture code are > >>> deliberately left for those later opt-in conversions. > > ... > >> Do you have a pointer at the arm64 part, so people can get a feeling for how an > >> actual hw_pte_t implementation can look like. > > > > May be we need the generic hw_pte_t implementation as { pte_t pte; } > > right away? > > Indeed, that makes sense. We just need a way for the architecture to opt-in that > it did the conversion. > > > > > Also, can you envision a case when sizeof(pte_t) != sizeof(hw_pte_t)? > > If not, the compile-time check is worth adding. > > That wouldn't work as is. We'd have to intercept ptep++ and instead have a > helper to advance the ptep pointer. I think I am missing the point. That is my takeaway from your previous mail: https://lore.kernel.org/lkml/31d36023-d728-4eee-90f8-158c7066f565@kernel.org/ > { > page_table_check_ptes_set(mm, addr, ptep, pte, nr); > for (;;) { > set_pte(ptep, pte); > if (--nr == 0) > break; > - ptep++; > + ptep = hw_pte_next(ptep); We should really just let ptep++ work as before. > pte = pte_next_pfn(pte); > } > } So are we going after hw_pte_next(ptep) or ptep++? > One idea for that would be to let the compiler catch that by marking hw_pte_t an > undefined struct (unknown size), such that the compiler would indicate any usage > of ptep++ properly. What is the purpose of that? I mean when pte_t vs hw_pte_t uses are sorted out what is the benefit of preventing hw_ptep++? > That can be done when it would actually required, so as a first step having a > generic hw_pte_t would just work. > > -- > Cheers, > > David Thanks!