From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 12F7D277021; Tue, 6 May 2025 10:49:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746528600; cv=none; b=Nb1jMHncvzWVt2xQnwu0IvDM332Tl9Vx169ggQI8hFvBPsvYIfnYH8wWe3zhk6zf+Pi6kofpUH1oOHict/FniEtubqChHI7kSKwq8oMu4VIOOqPcI0wxRUHnovVMIo100xP3/pICgwAocf7mPFwsnTuoopKOyJVe6eo078+9vt4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746528600; c=relaxed/simple; bh=Yl8x0S4VxmXIn6uRpFGrPJ5DjxjPXmgnerWYsgAOvmQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jdiKJgJf2YlPn6zp+1SwiYpGS+Dvk2CRzer/CZEsODgf2mHNuvuwFrSp/et/MZ4nDi/pchixvWG29BbOBgAlGqmZn4ZpQGYuDbaq8LGlXQL5hoF4FPVpt8KxcrwVcTjKCorVB9Okb0dV2CYOMiRI9tRL4k6ajENcTnoPyUkg/oE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71191C4CEF0; Tue, 6 May 2025 10:49:56 +0000 (UTC) Date: Tue, 6 May 2025 11:49:54 +0100 From: Catalin Marinas To: Yeoreum Yun Cc: Ryan Roberts , Ard Biesheuvel , 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, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, stable@vger.kernel.org Subject: Re: [PATCH v2] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation Message-ID: References: <20250502180412.3774883-1-yeoreum.yun@arm.com> <174626735218.2189871.10298017577558632540.b4-ty@arm.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: On Tue, May 06, 2025 at 11:47:44AM +0100, Yeoreum Yun wrote: > > On 06/05/2025 10:41, Ard Biesheuvel wrote: > > > On Tue, 6 May 2025 at 10:16, Ryan Roberts wrote: > > >> > > >> 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. > > >> > > > > > > Indeed. > > > > > >> 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. > > >> > > > > > > The issue is that the store occurs via the ID map, which only consists > > > of one R-X and one RW- section. I'm not convinced that it's worth the > > > hassle to relax this. > > > > > > If moving the variable to .data works, then let's just do that. > > > > Yeah, fair enough. > > Thanks. > I've success to reproduce. and after check, Sending with this fix. No need to resend, I modified it locally. Thanks. -- Catalin