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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gQRl7YUQCBVoiNIinaXRRJ6iLdSG3Rzd0xV0hEu2lGo5w6z86vYyNhkSIYX9L3nd9 q4q4/O6JNDXm4XNPNif4MOp4E6vcDqWFBACswg6z3701KGFgiJeJvUAoj008c2kew8 5BJk9bAjoi8xDDesBwIO6jPMcRzOrdrOp8BTmyaQ= Date: Thu, 16 Jul 2026 08:49:47 +0100 From: Yeoreum Yun To: Geert Uytterhoeven Cc: Yeoreum Yun , Dave Hansen , "David Hildenbrand (Arm)" , 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, 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: <31988089-095a-4eed-b5e2-c677c70f79f6@kernel.org> <14e250db-1641-4085-8d13-02f819657d5f@intel.com> <6df814c9-405c-48d8-96ea-929c4b28949b@intel.com> Precedence: bulk X-Mailing-List: linux-arch@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: On Wed, Jul 15, 2026 at 12:34:29PM +0200, Geert Uytterhoeven wrote: > Hi Yeoreum, > > On Wed, 15 Jul 2026 at 11:42, Yeoreum Yun wrote: > > > On Tue, 14 Jul 2026 at 18:51, Yeoreum Yun wrote: > > > > --- 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; > > > > + > > > > + if (mm_pmd_folded(mm) && level == 3) > > > > + return true; > > > > + if (mm_pud_folded(mm) && level == 2) > > > > + return true; > > > > + if (mm_p4d_folded(mm) && level == 1) > > > > + return true; > > > > > > Is this order (... && level == ...) the optimal order? > > > On arm64, mm_pud_folded() and mm_p4d_folded() perform several checks. > > > > > > > + if (level == 0) > > > > + return true; > > > > + > > > > + return false; > > > > +} > > > > It is. since the purpose of ptdump_pt_level_first is designed to be used > > in the *callback* of pXd_entry(). IOW, if we check level 0 first, > > it always returns wrong return in folded case. > > I meant the order inside the if () conditions. > E.g. > "if (mm_pud_folded(mm) && level == 2)" does the expensive check first. > "if (level == 2 && mm_pud_folded(mm))" does the cheap check first. Ah. Yeap that would be better. Thanks! -- Sincerely, Yeoreum Yun