From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 5A50B23F42D for ; Tue, 6 May 2025 08:15:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746519357; cv=none; b=PJ7fSeM9gLL3JJ6wPP6Kqn4Z4DR+pFR/zLAIPJvrSM81h1KafyxaJiQ0R49LYmUkjiQ3cnx6tv3eSHCs1gQRzcHaAwkej4lczKm9WxCQO/LZ5XNJSBGekVSclTtmvJUeCvK/DiJ9/lW99nXWlzAyzeQiUbu7UBhcffSKDQWPMwg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746519357; c=relaxed/simple; bh=CfZVKeYNbfhVnlmmFxZfDkwiP+Fo3N99MhQ1aFcsCG4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GikHHqKcZmkqXmHANcMGKRlH6t0tXPfe/aUE0Of27SshujKq/IKfdqmyyFSBHOSdb6WOWwYIccF512lsN4ObjkRdAi3X2iFQfyc3lxb3vcCpoTBFr2VqBXUiO0LgRIG8y2gbCMB353xVA6i5LM4pB0Ik5z9A7QLNFOZHNg3+2pw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CCE39113E; Tue, 6 May 2025 01:15:44 -0700 (PDT) Received: from [10.57.93.118] (unknown [10.57.93.118]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 338A43F673; Tue, 6 May 2025 01:15:50 -0700 (PDT) Message-ID: Date: Tue, 6 May 2025 09:15:48 +0100 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation Content-Language: en-GB To: Yeoreum Yun , Catalin Marinas Cc: will@kernel.org, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, morbo@google.com, justinstitt@google.com, broonie@kernel.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, shameerali.kolothum.thodi@huawei.com, james.morse@arm.com, hardevsinh.palaniya@siliconsignals.io, ardb@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, stable@vger.kernel.org References: <20250502180412.3774883-1-yeoreum.yun@arm.com> <174626735218.2189871.10298017577558632540.b4-ty@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 06/05/2025 09:09, Yeoreum Yun wrote: > Hi Catalin, > >> On Sat, May 03, 2025 at 09:23:27PM +0100, Yeoreum Yun wrote: >>> Hi Catalin, >>> >>>> On Sat, May 03, 2025 at 11:16:12AM +0100, Catalin Marinas wrote: >>>>> On Fri, 02 May 2025 19:04:12 +0100, Yeoreum Yun wrote: >>>>>> create_init_idmap() could be called before .bss section initialization >>>>>> which is done in early_map_kernel(). >>>>>> Therefore, data/test_prot could be set incorrectly by PTE_MAYBE_NG macro. >>>>>> >>>>>> PTE_MAYBE_NG macro set NG bit according to value of "arm64_use_ng_mappings". >>>>>> and this variable places in .bss section. >>>>>> >>>>>> [...] >>>>> >>>>> Applied to arm64 (for-next/fixes), with some slight tweaking of the >>>>> comment, thanks! >>>>> >>>>> [1/1] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation >>>>> https://git.kernel.org/arm64/c/12657bcd1835 >>>> >>>> I'm going to drop this for now. The kernel compiled with a clang 19.1.5 >>>> version I have around (Debian sid) fails to boot, gets stuck early on: >>>> >>>> $ clang --version >>>> Debian clang version 19.1.5 (1) >>>> Target: aarch64-unknown-linux-gnu >>>> Thread model: posix >>>> InstalledDir: /usr/lib/llvm-19/bin >>>> >>>> I didn't have time to investigate, disassemble etc. I'll have a look >>>> next week. >>> >>> Just for your information. >>> When I see the debian package, clang 19.1.5-1 doesn't supply anymore: >>> - https://ftp.debian.org/debian/pool/main/l/llvm-toolchain-19/ >>> >>> and the default version for sid is below: >>> >>> $ clang-19 --version >>> Debian clang version 19.1.7 (3) >>> Target: aarch64-unknown-linux-gnu >>> Thread model: posix >>> InstalledDir: /usr/lib/llvm-19/bin >>> >>> When I tested with above version with arm64-linux's for-next/fixes >>> including this patch. it works well. >> >> It doesn't seem to be toolchain related. It fails with gcc as well from >> Debian stable but you'd need some older CPU (even if emulated, e.g. >> qemu). It fails with Cortex-A72 (guest on Raspberry Pi 4) but not >> Neoverse-N2. Also changing the annotation from __ro_after_init to >> __read_mostly also works. I think this is likely because __ro_after_init is also "ro before init" - i.e. if you try to write to it in the PI code an exception is generated due to it being mapped RO. Looks like early_map_kernel() is writiing to it. I've noticed a similar problem in the past and it would be nice to fix it so that PI code maps __ro_after_init RW. Thanks, Ryan > > Thanks to let me know. But still I've failed to reproduce this > on Cortex-a72 and any older cpu on qeum. > If you don't mind, would you share your Kconfig? > >> I haven't debugged it yet but I wonder whether something wants to write >> this variable after it was made read-only (well, I couldn't find any by >> grep'ing the code, so it needs some step-by-step debugging). >> > [...] > > Thanks! > > -- > Sincerely, > Yeoreum Yun