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Tue, 14 Jul 2026 10:26:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id PH4iO9IOVmoNJQAAD6G6ig (envelope-from ); Tue, 14 Jul 2026 10:26:26 +0000 Date: Tue, 14 Jul 2026 11:26:20 +0100 From: Pedro Falcato To: Yeoreum Yun 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, david@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 02/34] ARM: mm: make 2-level pgd_t a scalar Message-ID: References: <20260713135614.1618183-1-yeoreum.yun@arm.com> <20260713135614.1618183-3-yeoreum.yun@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260713135614.1618183-3-yeoreum.yun@arm.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 95FD540007 X-Stat-Signature: mr7mt1g1ec8gsdda9dbtmh4q7aewm4rf X-HE-Tag: 1784024794-635686 X-HE-Meta: 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 cASRDm56 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 13, 2026 at 02:55:41PM +0100, Yeoreum Yun wrote: > From: "David Hildenbrand (Arm)" > > We don't want pgd_t to be an array, as it prohibits returning it from a > function, like pgdp_get(). > > So let's just use an u64, and extract the right 32bit value in > pgd_val(). > > Leave the STRICT_MM_TYPECHECKS case alone for now. I have to ask: is there a good reason for the STRICT_MM_TYPECHECKS ifdef? I see the compiler has an awkward time returning a u64 struct (see https://godbolt.org/z/qejbv6j9a), but if this doesn't work maybe we should get rid of the STRICT_MM_TYPECHECKS stuff? I seriously doubt anyone is purposefully toggling it on for testing from time to time. If STRICT_MM_TYPEDEFS's worse codegen doesn't matter then maybe we should permanently toggle it on. > > As an alternative, we could use the STRICT_MM_TYPECHECKS approach here > as well, but using an u64 looks conceptually cleaner, even though > pgd_val() gets a bit more involved. > > Signed-off-by: David Hildenbrand (Arm) > Signed-off-by: Yeoreum Yun > --- > arch/arm/include/asm/pgtable-2level-types.h | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/arch/arm/include/asm/pgtable-2level-types.h b/arch/arm/include/asm/pgtable-2level-types.h > index 650e793f41429..02052cef9437a 100644 > --- a/arch/arm/include/asm/pgtable-2level-types.h > +++ b/arch/arm/include/asm/pgtable-2level-types.h > @@ -25,7 +25,7 @@ typedef struct { pteval_t pgprot; } pgprot_t; > > #define pte_val(x) ((x).pte) > #define pmd_val(x) ((x).pmd) > -#define pgd_val(x) ((x).pgd[0]) > +#define pgd_val(x) ((x).pgd[0]) > #define pgprot_val(x) ((x).pgprot) > > #define __pte(x) ((pte_t) { (x) } ) > @@ -36,14 +36,21 @@ typedef struct { pteval_t pgprot; } pgprot_t; > /* > * .. while these make it easier on the compiler > */ > +typedef u64 pgdval_t; > + > typedef pteval_t pte_t; > typedef pmdval_t pmd_t; > -typedef pmdval_t pgd_t[2]; > +typedef pgdval_t pgd_t; > typedef pteval_t pgprot_t; > > #define pte_val(x) (x) > #define pmd_val(x) (x) > -#define pgd_val(x) ((x)[0]) > + > +static inline pmdval_t pgd_val(pgd_t pgd) > +{ > + return (*(pmdval_t (*)[2])&pgd)[0]; Ugh. This isn't correct C code. It only works because the kernel passes -fno-strict-aliasing. I would recommend either forcing a struct here, or using a u64 with bitmasks/shifts. -- Pedro