From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 40D5239CCFA; Tue, 14 Jul 2026 17:29:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784050196; cv=none; b=BF/8xydJILkAR/k6Z7+vGbXUZOoC5GL8LCTL5M1VFDiLv3PgXWBrw0aiCu8QYSXXOPAMcfNNk0cuZeGbKU0YV3ZIS9MCiW1wY5kqwa4N5gQsTrKnJJqanZMr3cvHYxPt37KOmnj+QLrFiBZNvyD2sZLFonVFobcIfFaD0rhb/+w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784050196; c=relaxed/simple; bh=tyBvsKgiolRX2x25K0xyzsGT+2C9trtefI8B7z5tDds=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=encAClfGtpAJG/FiUPJiUmnyTFBukyiDFWQnNAUeFMhuqHFSqGAb/R7FhVvqKnF+Bbmr+B8BSGRmNTD3Xeb/p0tOuGXym1fd5jsCBR9/PE9yTpoFiDie+4/FJuUbspha+AXEEws7iewNN4DAzL0f5Tr5DP2zGcooiijd3nhD/4Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oCpbhHVh; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oCpbhHVh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C79E81F00A3A; Tue, 14 Jul 2026 17:29:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784050194; bh=h6oib2F+Iwq8XkLAzZaDDtV/NgT4fqcpJDZGEXaDTLY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=oCpbhHVhU4YG1EeK5Mz8gwjp70/H/XZioXNfwY6KQGIV744BEsChOpGqBZ8hoQ5gf KfZRyQmXX8NMQ+6wq2bWCuxEbfMkdAWl5S64hnBs3vj8SqdX8gCSRQSlj9+WzEfggN XQsswnB1jtSaKMzPL/20kSHSl/doBxDOleyFt2lh54MYhxGEgV1Vywy2JN6ZizZ7nt G70zTfHbhplWuTD/b3sl/K0/E9dUT8DwrX+7QZ0fGydgHy2WeVb0ADFW2SvAk4L9Ok aLxx3ML9nCJtJpwMslU9iCwIvJBuqDr6bwEKGe5N1fdBmpsG/zbIgCK1/XhoOQNWC6 YzP+yqCn4XBBg== Message-ID: <7cff02d6-d3ce-4315-b667-34911fc6f321@kernel.org> Date: Tue, 14 Jul 2026 19:29:38 +0200 Precedence: bulk X-Mailing-List: linux-arch@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: Yeoreum Yun , Dave Hansen Cc: 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 References: <6007625e-c3f9-4ad6-99a8-61396bccbcec@kernel.org> <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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/14/26 18:51, Yeoreum Yun wrote: > On Tue, Jul 14, 2026 at 05:08:24PM +0100, Yeoreum Yun wrote: >> On Tue, Jul 14, 2026 at 07:35:19AM -0700, Dave Hansen wrote: >>> >>> This is indeed an improvement and a step in the right direction! Thanks >>> for looking at this. >>> >>> But one of my test for whether it's good x86 code is whether there's any >>> actually x86-specific logic in it. Isn't this basically a translation >>> between the integer level number and whether it is folded? >>> >>> That seems like a common helper that more than one arch could use. Could >>> this be stuck in a helper so that all arch/x86 has to do is: >>> >>> if (mm_pt_level_folded(mm, level)) >>> return; >> >> Yes. at least the level semantic in ptdump (pgd is level 0, >> p4d is level 1, ...) is same to all archs where use ptdump. >> So It seems reasonable to add this common helper in ptdump.c >> > > Furthermore, the effective_prot() need to require to identify whether > it's the first pgtable to prevent the inheriting from dummy value. > So I think it seems to make a ptdump_pt_level_first() like: > > diff --git a/mm/ptdump.c b/mm/ptdump.c > index 973020000096c..2ec5700e4be5e 100644 > --- a/mm/ptdump.c > +++ b/mm/ptdump.c > @@ -190,6 +190,23 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd) > st->note_page_flush(st); > } > > +bool pdtump_pt_level_first(struct mm_struct *mm, int level) > +{ > + if (!mm || level > CONFIG_PGTABLE_LEVELS) > + return false; Do we actually ever get !mm ? -- Cheers, David