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 D5C7BC44501 for ; Mon, 13 Jul 2026 19:50:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8B1EA6B0005; Mon, 13 Jul 2026 15:49:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 83B906B0088; Mon, 13 Jul 2026 15:49:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6DEDA6B008A; Mon, 13 Jul 2026 15:49:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 273436B0005 for ; Mon, 13 Jul 2026 15:49:59 -0400 (EDT) Received: from smtpin16.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 6E733140160 for ; Mon, 13 Jul 2026 19:49:58 +0000 (UTC) X-FDA: 84984794076.16.A3E1860 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf10.hostedemail.com (Postfix) with ESMTP id AA4DFC0007 for ; Mon, 13 Jul 2026 19:49:56 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=LvSI84Kp; spf=pass (imf10.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783972196; 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:dkim-signature; bh=IZe9zYBUgL5Fku0tOf4jGfW4HRaI0/J5FQVtBy0Ve6I=; b=Ob87qK2am2+vLivuAbY2s5EFn8J38Qdtidpv4hNXzS9fAMMPturLrtn9/LslSFzOUXi0wV g0xEF0uWhSctGX/hpAK7o3ckVqS50DpX5s62XbOFK2HSYRafPU48FZgnSgFe2giCia+j+m FBAtpchQL83PGT5S+EGISTE4P2KDwr4= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=LvSI84Kp; spf=pass (imf10.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783972196; b=KF5OVGbAl6gEh31m9zdKZYVN5OuoJiDKSgyTuwjC/T68+C2tvQ96MQKH9s7rQ7UDsgDCly x+wd3QYa00DNQ3SpNzmTCiR1/d8s8gUmp11tJBAzB6WuTIUGb67W5MeOgH0mZNrGroTxiL ZjjlVASvaYC/4VXAlbJjXePRHnyuweE= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 0E94060103; Mon, 13 Jul 2026 19:49:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88C921F000E9; Mon, 13 Jul 2026 19:49:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783972195; bh=IZe9zYBUgL5Fku0tOf4jGfW4HRaI0/J5FQVtBy0Ve6I=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LvSI84KpyEW4PF6a7LNDng1GF+rwXXsJKi7/6liu+LAH2SvyPUp3Y3dazy85hfiJ2 8wmORaiWbxnT9QD4Gktp63fmyZHYGlJwN0LNqE9aW/GK3kqC9X/vUDxMT2Dh2t1JkM YdU53xX2zJldz/W8YkvqFYp3XZ6jIqIACguCJ9Paeh/RuCinRwhFichfxdD0IQw8AI uzF+0XEdW14nQUGG2j3iuaQeox3i/AnIlQp+tfHaGhsUjH1ROQ6M8kUvkdg6XHz0xG 0JTaMX5GR3Vnw/gkw8JisANxpqabirohlF5apD06wIS/ws1h48ypbW2+WJUaYP+JQn 0DyzG/pm3fC1Q== Message-ID: <3ea30f8a-bb29-4bf5-8400-1c4840d46a88@kernel.org> Date: Mon, 13 Jul 2026 21:49:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 10/34] x86: mm: carve out the generic compile-time folded pgtable case in effective_prot() To: Dave Hansen , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-arch@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, linux-csky@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-openrisc@vger.kernel.org Cc: linux@armlinux.org.uk, akpm@linux-foundation.org, ankur.a.arora@oracle.com, rppt@kernel.org, linmag7@gmail.com, chleroy@kernel.org, klarasmodin@gmail.com, chenhuacai@kernel.org, kernel@xen0n.name, kas@kernel.org, zhangtianyang@loongson.cn, wangyuli@aosc.io, tsbogend@alpha.franken.de, ljs@kernel.org, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, ryan.roberts@arm.com, pasha.tatashin@soleen.com, rmclure@linux.ibm.com, baolin.wang@linux.alibaba.com, tj@kernel.org, kevin.brodsky@arm.com, anup@brainfault.org, atish.patra@linux.dev, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, hannes@cmpxchg.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, ryabinin.a.a@gmail.com, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, anshuman.khandual@arm.com, yang@os.amperecomputing.com, chaitanyas.prakash@arm.com, ardb@kernel.org, guoren@kernel.org, yang.li85200@gmail.com, viro@zeniv.linux.org.uk, dinguyen@kernel.org, schuster.simon@siemens-energy.com, wangruikang@iscas.ac.cn, junhui.liu@pigmoral.tech, muchun.song@linux.dev, vishal.moola@gmail.com, namcao@linutronix.de, pavel@kernel.org, djbw@kernel.org, yu-cheng.yu@intel.com, baolu.lu@linux.intel.com, Jonathan.Cameron@huawei.com, coxu@redhat.com, andreas@gaisler.com, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, geert@linux-m68k.org, shorne@gmail.com, jonas@southpole.se, stefan.kristiansson@saunalahti.fi References: <20260713135614.1618183-1-yeoreum.yun@arm.com> <20260713135614.1618183-11-yeoreum.yun@arm.com> <710b7eb0-8e0c-4f07-991c-2285c77e1beb@intel.com> <6007625e-c3f9-4ad6-99a8-61396bccbcec@kernel.org> <32d459d1-ad19-4baf-bbb1-0565458001d2@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <32d459d1-ad19-4baf-bbb1-0565458001d2@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: AA4DFC0007 X-Stat-Signature: w4beauts9pqwcuba8n99i6bmth61kumf X-HE-Tag: 1783972196-417518 X-HE-Meta: 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 qycZLoaN ql6ueDl6sjjdTjtR+Gp3+pOob2Y56EOjiVpA0ljv7kbMIpYBV7DD7HTnRvPHysDtUlAPEyM8BpGnLUFsJZOmNJFS3Qs1QfjvPg98S3WxJNgBDfYz/Meex/+E+K0Jj/XbhQuuzY3Kp2BQ6/fqwCNZplNcrEI3SIRWtu8HOM/J9XMm3/KI549DBDRCwe7S5ecXg+Q/q2CKLloN/rkYCRF4hpqNjfloQuXXoOiPzYd5LuUk1ekyuQeOCRFFWUEr1yR6lrdk34GS/P+50m/MyyepoiwfknT3+jy2CSEvSRB/tuREA3mWoybt3+B3HJnV6ANhxWgj3O25d/MNFUiLNJR1NgNbFXIfY4Ks92iKhcnJ1JzVg2n2MSjG1xpd6fcLEx1FhlRtS Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/13/26 19:57, Dave Hansen wrote: > On 7/13/26 08:02, David Hildenbrand (Arm) wrote: >> It's always been the latter: >> >> ...folding => PUD => PMD => PTE > > This is kinda arguing semantics, and there are different ways to look at > it. But I'd argue it couldn't *possibly* have always been this way. > Linux hasn't always had a PUD or a PMD for that matter. The i386 only > had two levels. PAE support was added later. > > I think the pmd_t came with Alpha support (before my time) and pud_t > came later IIRC. I'm pretty sure Linux didn't have a pud_t when I first > started hacking on it circa 2001. Yes, I'm sure there is some horrible, horrible history to how we came to what we have today :) > > Second (and again this is my subjective opinion) a pgd_t* has always > been the "top" or "base" of the page tables. This is why there's an > mm->pgd and not an mm->pud. We've also talked *forever* about things > like a "special pgd" for the LDT remap. Or having two pgd pages for KPTI. Agreed. We always called it pgd, which is just an alias to p4d/pud etc really. > > My point is that the PGD hasn't itself ever been folded. It's the top > hardware level of the page tables and always has been. With the history in mind, yes. Looking at the current state it's more complicated. Because pgd_present() are really just dummy functions. And this series proposes to let also pgdp_get() be a dummy function and disallow something like set_pgd(pgdp_get()) Which is just asking for trouble. Similar with using pgd_page(pgdp_get()) on We could get away with catching that case similar to how we catch pgd_offset() abuse, but I'd rather try get rid of the wrapper functions set_pgd() / pgd_page() entirely. But if we feel like that is too much, we can look into that direction. > > I really do think this series is changing things, not keeping them the same. Looking at it from that angle, I tend do agree: it further moves into the direction that actually the p4d_present() carries value, and the previous pgd_present() is just a dummy. I can see that some more work is required to untangle the mess we already have. I don't know why pgd_present() was made a dummy function and not p4d_present(), but I'm sure there is a good reason to it. Changing that now ... omg. -- Cheers, David