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b=bnBSYp007P3L0wbtoXgGfxFvsLp4tsGHwrC12gp4KjH6ljYnZ0RBjSDF5M5pnmvuO IQJ3Rx6RBpIm+JzkohNZdbqCP06ezF6UpF9zPwHoSJ1Xd6U4rZA/gMDAY2Jyzxidpm SZ1CXfJ1sjFaRFFkaGILplnO6B2e/EQs4RpQTDDK/p125mtmvZMGUUCctk6maQDOoq 2TEUViz+2i5GU5Vyz0mqub2TyjXhAVzJNdZS7MGgEre0oapyl/ENAR2FRfa1pDxghq Rn/FbvCnr5Ng8YtNdBVy8Q/nP/TGA4Wfj3GvdAxYMjX9e6ab7HmcnWA4c2XqyLdr/e fBzLU/vO1pLkw== Message-ID: <6007625e-c3f9-4ad6-99a8-61396bccbcec@kernel.org> Date: Mon, 13 Jul 2026 17:02:47 +0200 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: Dave Hansen , Yeoreum Yun , 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 Cc: 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: <20260713135614.1618183-1-yeoreum.yun@arm.com> <20260713135614.1618183-11-yeoreum.yun@arm.com> <710b7eb0-8e0c-4f07-991c-2285c77e1beb@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 X-Rspamd-Queue-Id: 53D2C4000A X-Rspam-User: X-Stat-Signature: hry9foxinn1mhi8jk856ii9z6zmgrzho X-Rspamd-Server: rspam03 X-HE-Tag: 1783954984-113254 X-HE-Meta: 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 Yvw33ut2 pvnYwFZ87vDQDzFkhxxhxOA6cgR1aMmIanxlezsow1UMp8sm4y6PYo8D4BVW7GCG8IzSGBsYizNl7Hf6Vryz4LwUuvQOAmiB9HsWndDiUTn953lAMAH8UzaBtRv7OtxsPyh0gkFeaBNaqVu50yepKq355uPveJ6U7jdX2T3UUZr4yBfmBaFCLxbu89NSDxozc5fwuzOxMFhYDscwgTjk2IyyHsPiXLOVUuVgQc2iNwoYydr6Q4aYWIYIeWGk2QDWza7CEheaE0OodNRqdcJRvJi1LykLM4YXa0E6oF9R7j7NlHVN9XjdDx4/+pmURHtwtDeqmw5LvBXl1jA7/EkBHyzdWZ+mpBulJWKwwiRjkJsa3Z7TD0bq83ytPPnra/YPwWcoO Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/13/26 16:55, Dave Hansen wrote: > On 7/13/26 07:41, David Hildenbrand (Arm) wrote: >> Essentially, we have to teach x86 code to ignore levels that are folded (e.g., >> pgd, p4d) and start collecting effective prots from the actual first non-folded >> level. > > I guess that's what the series really comes down to. > > The model is moving from (using 3-level PAE as an example): > > PGD => ...folding => PMD => PTE > > to > > ...folding => PUD => PMD => PTE > > Right? Not quite, because it's complicated: static inline int pgd_none(pgd_t pgd) { return 0; } static inline int pgd_bad(pgd_t pgd) { return 0; } static inline int pgd_present(pgd_t pgd) { return 1; } static inline void pgd_clear(pgd_t *pgd) { } #define p4d_ERROR(p4d) (pgd_ERROR((p4d).pgd)) #define pgd_populate(mm, pgd, p4d) do { } while (0) #define pgd_populate_safe(mm, pgd, p4d) do { } while (0) It's always been the latter: ...folding => PUD => PMD => PTE This series rather enforces that the latter is used consistently. (e.g., not working on pgds when they are actually always look like present page tables) We decided to go for strict BUILD_BUG() on set_pgd() etc. because otherwise it's just waiting for trouble once we change what pgpd_get() returns. -- Cheers, David