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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=G0RUjlJz3owlWeTlpPV8u3FIp5RuBGK/3NB7wbcP+UXQAmCYCXmS34xYdScxVlpRC 0bRxrex7ATIWiVwavRFx8SXG/TT09iNUF63YzL6JCoJZGGx+GkRwGDdjMbNE7EKjBK y4iGiJK1D0syrrUl+zvzYTCLcyhE/eREzIUSEcVU= Date: Wed, 15 Jul 2026 10:41:47 +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: <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> Precedence: bulk X-Mailing-List: linux-kernel@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: Hi Geert, > Hi Yeoreum, > > On Tue, 14 Jul 2026 at 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: > > > > On 7/14/26 04:40, Yeoreum Yun wrote: > > > > > @@ -254,22 +255,8 @@ static void effective_prot(struct ptdump_state *pt_st, int level, u64 val) > > > > > struct pg_state *st = container_of(pt_st, struct pg_state, ptdump); > > > > > pgprotval_t prot = val & PTE_FLAGS_MASK; > > > > > pgprotval_t effective; > > > > > - bool first_level = false; > > > > > > > > > > - /* Ignore folded levels ... */ > > > > > - if (((level == 0) && mm_p4d_folded(st->mm)) || > > > > > - ((level == 1) && mm_pud_folded(st->mm)) || > > > > > - ((level == 2) && mm_pmd_folded(st->mm))) > > > > > - return; > > > > > - > > > > > - /* ... and make the actual first level remember the protection. */ > > > > > - if (((level == 0)) || > > > > > - ((level == 1) && mm_p4d_folded(st->mm)) || > > > > > - ((level == 2) && mm_pud_folded(st->mm)) || > > > > > - ((level == 3) && mm_pmd_folded(st->mm))) > > > > > - first_level = true; > > > > > - > > > > > - if (!first_level) { > > > > > + if (first_level > st->first_level) { > > > > > pgprotval_t higher_prot = st->prot_levels[level - 1]; > > > > > > > > > > effective = (higher_prot & prot & (_PAGE_USER | _PAGE_RW)) | > > > > > @@ -471,6 +458,15 @@ bool ptdump_walk_pgd_level_core(struct seq_file *m, > > > > > .seq = m > > > > > }; > > > > > > > > > > + if (mm_pmd_folded (mm)) > > > > > + st->first_level = 3; > > > > > + else if (mm_pud_folded (mm)) > > > > > + st->first_level = 2; > > > > > + else if (mm_p4d_folded (mm)) > > > > > + st->first_level = 1; > > > > > + else > > > > > + st->first_level = 0; > > > > > + > > > > > ptdump_walk_pgd(&st.ptdump, mm, pgd); > > > > > > > > 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; > > + > > + 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. -- Sincerely, Yeoreum Yun