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X-CSE-ConnectionGUID: XtW/+JJGTneGoJG61DRHqQ== X-CSE-MsgGUID: bJzR+3kcRyqIcUJfHpWLAw== X-IronPort-AV: E=McAfee;i="6800,10657,11841"; a="84459204" X-IronPort-AV: E=Sophos;i="6.25,154,1779174000"; d="scan'208";a="84459204" Received: from orviesa008.jf.intel.com ([10.64.159.148]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Jul 2026 10:57:18 -0700 X-CSE-ConnectionGUID: pKvhLf9LTu+eHV+HNZK7iA== X-CSE-MsgGUID: BWtH56OzTBSLHcmLMAMQ4w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,154,1779174000"; d="scan'208";a="255108504" Received: from smithj1-mobl2.amr.corp.intel.com (HELO [10.125.108.83]) ([10.125.108.83]) by orviesa008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Jul 2026 10:57:16 -0700 Message-ID: <32d459d1-ad19-4baf-bbb1-0565458001d2@intel.com> Date: Mon, 13 Jul 2026 10:57:18 -0700 Precedence: bulk X-Mailing-List: linux-mips@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: "David Hildenbrand (Arm)" , 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> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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. 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. 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. I really do think this series is changing things, not keeping them the same.