From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D05952F7EF2 for ; Tue, 14 Jul 2026 18:29:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784053751; cv=none; b=Z79FbCgLCneGN+T6qt1sWY2YgbPGnwM9kQvPPLdDzPCnFYeV8AIhy8Eno80+TvqkYd9fsm5mAkr5XeAYIyljrJXUIXDnlXyvWCaHiAsUWQlv0ieFAXVe1T872jrwjaQP0hwfqRjY1nNQdE+xjRVTV4zAttksjxuqKKoDl/jidAU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784053751; c=relaxed/simple; bh=Q1RaqZFJWDyzCpzM1YydwuIkdx6+prWZv8uRlRqjdPI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Zdz+GkH3ONs/ics7G0RP/NrhsM3l7m7B4A6IwD+sw04brI6m8Cp2KLcYJVHE3Wr4FnPo7i0oSbz3GJe0y8f5yhoDhCnIhfUlBGiAuQT/L3uDvunxec0bxzcnIL5QzoEnGFAPLQ/bMx+DqPjmIsDqGTsdsmwWFpZSxyv6jDT9S+M= ARC-Authentication-Results:i=1; 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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qQBkYOYvll6kV7ChEqyEs9q4KbHl0/kv64+7ai5nhYymyDIN8BvOvG1HzfhI1sCcI qnEtCqga3FrW8+7FXBrXN5emMU1ez24iSDr20rEKRSLvtMZ9oCz/5VlGhBuCnHlKFi ME8BD+bOTZVCgK3PWVNAk87A3Vsa2vT+e5mfIs0s= Date: Tue, 14 Jul 2026 19:28:56 +0100 From: Yeoreum Yun To: "David Hildenbrand (Arm)" Cc: Yeoreum Yun , Dave Hansen , 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, 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 Subject: Re: [RFC PATCH 10/34] x86: mm: carve out the generic compile-time folded pgtable case in effective_prot() Message-ID: References: <32d459d1-ad19-4baf-bbb1-0565458001d2@intel.com> <3ea30f8a-bb29-4bf5-8400-1c4840d46a88@kernel.org> <7e84b200-25eb-43a6-b5e2-5f27f2d82a77@intel.com> <31988089-095a-4eed-b5e2-c677c70f79f6@kernel.org> <14e250db-1641-4085-8d13-02f819657d5f@intel.com> <6df814c9-405c-48d8-96ea-929c4b28949b@intel.com> <2d51a1ad-85be-46bf-ac36-18eca199b449@kernel.org> Precedence: bulk X-Mailing-List: linux-m68k@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: <2d51a1ad-85be-46bf-ac36-18eca199b449@kernel.org> On Tue, Jul 14, 2026 at 06:31:22PM +0200, David Hildenbrand (Arm) wrote: > > >> This makes a *ton* of sense in effective_prot() especially. Its entire > >> job is mirroring the hardware's job of inheriting permissions from > >> higher levels of the page tables and enforcing them on lower level leaf > >> entries. If a higher level is folded, there's nothing to inherit. > >> > >> I also think it's worth taking a brief pause on the coding to think > >> about what kind of design would actually be nice here. If the design > >> really is that the pgd is folded, the 'struct mm_walk_ops' code would > >> ideally not even call ->pgd_entry(). It would just (for example) *start* > >> at ->pud_entry() for a 3-level hardware page table. > >> > >> If there are no pgds, why bother calling ->pgd_entry()? It couldn't be > >> done transparently to mm_walk users of course but it could be done > >> incrementally where users move one at a time over to a new scheme. > > > > Agree. Calling a pXd_entry() about folded one seems meaningless. > > But seems enough to check mm_pXd_folded() before calling pXd_entry() > > in each walk_pXd_range(). > > Needs some double-checking that callers can handle it (like effective_prot() > would currently not), but certainly something to look into! Most of mm_walk_ops *implicitly* handles the folded pgtable case (e.x) pXd_none() / pXd_present() and other can handle explicitly in its own handler. But, IMHO, It would be better to skip calling pXd_entry() in the walk_pXd_range() by checking the folded and this is clearer conceptually. For this, it requires the rewrite the walk_mm() where use only *p4d_entry()* to gather the leaf/non-leaf information for MGLRU. -- Sincerely, Yeoreum Yun