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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Sy24kfg6zd8pNJNRop/ip6vK3z44QuvSe+ei7yBDMgOJ+AmuCVqSqQsYm6AbuGoqC lZJ+hB5IynonlF0Xd5xFhRT6j05I3fGK7eqV9iwp4S7UfNaW857WlXcvL4lT3vU6jA Qslx6H13Q5aAiK/4ThVrFPZNAc560M7EpnY0APes= Date: Tue, 14 Jul 2026 18:58:57 +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: <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> <7cff02d6-d3ce-4315-b667-34911fc6f321@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7cff02d6-d3ce-4315-b667-34911fc6f321@kernel.org> X-Rspamd-Queue-Id: 8066040003 X-Stat-Signature: 4xcufpbkg749h6384taag3rbe53f3wrc X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1784051951-296178 X-HE-Meta: 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 iGXS2mYU N/M0SlN6FKEftQ4DAr2pLTFo5TER3EzlpF5+Dt+3xuctfKjD6nToJ/fOdd5aIZnIsiymMxCq1Ui+CNJfUtmw7UEC0dtQ3Chbna3H2EFAA1Gud3abiba6bR1gHgdCqRvMtfkZT29Q+7tJCbLrS0NiQkZ7ibw+VdNMrRWzVIMWdp/ig8TWlRbXxsZIil2EwFm6mq75YK1ctxOwUg3rr7WBrJZujQOpm/jex45FK+2FQrkRF7YMKIy+N8Lp5kbH1B/pt1AT4YoelD0WYfTPaAl1mn/FsuDAB6+wkbHgGxV87NO+kXFXGn8xfY9bHD042QYrnTtrio7uphFqiOU6xbaFWL4ibAXnbEV/YT9N9u+2dY6X2S1Q= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 14, 2026 at 07:29:38PM +0200, David Hildenbrand (Arm) wrote: > 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 ? Yes. for the case of s390 use mm anyway for folded check. > > -- > Cheers, > > David -- Sincerely, Yeoreum Yun