From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B7B76466B77; Tue, 14 Jul 2026 13:03:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784034228; cv=none; b=YJ++smG2VoTohP2ebeFUjGhTj0Esg7de5Ky1PRR/Ez9posANDWI+Hj4RLOAL8lYvoyIw8Ph+isrXWMkQIqts63zPXzur1sw/3gafZj1V7cITauZG6/cWk9hEY8j799fmh1paaqtg4WLzzqV+hkvo6H8RNTN+UFoNoaGLL3p6+Kw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784034228; c=relaxed/simple; bh=d0IMXuHc42au3G7lJdtmyd1ldUbkbqxBPxZonTqjkcM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=p3bSmzd72/SQXiHYHSAWokNGdul2ZW1pxE64KOCmpA36YpR2Urh4enffPpmyhMCyfUTdxhNjeXxbwpa46FIPTk0KaXUjXeGdrSnABuO+lUJMIShamcm3JEMfQwtRLZpIc2nHZZqcuuCa5uWK24MsIxrABStT/WAJuChhSyzKOY4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ddGyknup; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ddGyknup" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 587281F000E9; Tue, 14 Jul 2026 13:03:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784034224; bh=jWi7hqyYTbzO1/N8hNuw+3aCqzWSHoGEXiSIX2DNwFo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ddGyknup29KvGfQGIfEwqFGZ1d4WWXQIGRtrE9OBzjxL9Xd5BK3gttkewgrGTwbiL NSk8Zcv3meMLAjy0eCgXXMtcGhvakuD2PtTuuiPL5xd9U6yhj3uWoReue0sc05+ZVV 9Fos/z1NtDQJGC2dZCMRTg7VozDKZqjrye+LSnwqd22EHIsaWMzAYs+Y9tZzTujqTb 3M2/1Ivgo4ZY0qHAHmGFoqX6ixQRbeLA6bIToa4Wm4Dh3db/n/585AZFwIigaeQFxN 3T3p1A92MU030ioQLguXyDW+g2niZAtU5QtzovFMDS2PpF0W/nHjlatlwL+SdrRFpk GKw2afA4K4BxA== Message-ID: <1d49594c-3549-482d-8c11-fdeb2051e952@kernel.org> Date: Tue, 14 Jul 2026 15:03:28 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 02/34] ARM: mm: make 2-level pgd_t a scalar To: David Laight , 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, 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> <20260713135614.1618183-3-yeoreum.yun@arm.com> <20260714133415.78e25654@pumpkin> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/14/26 14:34, David Laight wrote: > On Mon, 13 Jul 2026 14:55:41 +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(). > > If you use a two element structure the compiler/ABI might be able to > return that from a function in two registers. > That might make the entire mess more readable ... The patch description states: " 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. " Arnd replied on that in more detail. Maybe I should just go back to using bit shifts and handing endianess. -- Cheers, David