From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4CC3DC64ED8 for ; Mon, 27 Feb 2023 16:17:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Subject:Cc:To:From:Date:References: In-Reply-To:Message-Id:Mime-Version:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=p9CdqbaxTVJyA0BpCAsYizqf9VGCX2IT6lZqHPwsGMQ=; b=03WzCgj1YZlCBP KaYGuiax/dX4oxBqWKKQ+Hbixqr/+AyQac25hPQLSaJ1MX6c4FJNh24Sb6a2c3RJlGjtUu8XqgJdl Rx1S1JpPxAXpy1hg7QRoLWcBc2pE/9Sdd76UBX8RttPtntK0ElAg4D6ipdElVwFIYTWxgOR2FwX61 q1gZMb0Z/+rILgPQGy2Fjh+hYIJCppB9QWW7QSKrFSK7i0CGlrrFDrhTEfRcoi0Szjeya+6jm8c5p Jni2MFpTM+/Llrjgz0dsO5xBgXJLy3EutJKCjiCrkjnglud6K7DMh3y3vWbWUSRtkBxM1Xm44wDyQ r2fyI9Ijf7tPgSsAPHoA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pWgAw-00AJum-Bm; Mon, 27 Feb 2023 16:16:30 +0000 Received: from wout3-smtp.messagingengine.com ([64.147.123.19]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pWgAs-00AJsl-8P; Mon, 27 Feb 2023 16:16:27 +0000 Received: from compute6.internal (compute6.nyi.internal [10.202.2.47]) by mailout.west.internal (Postfix) with ESMTP id 3AA09320091D; Mon, 27 Feb 2023 11:16:20 -0500 (EST) Received: from imap51 ([10.202.2.101]) by compute6.internal (MEProxy); Mon, 27 Feb 2023 11:16:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arndb.de; h=cc :cc:content-type:date:date:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:sender:subject :subject:to:to; s=fm3; t=1677514579; x=1677600979; bh=gyEHnWGhDf Ft2Gu4gB/Bqdx54bxIG396QI5JbNzq7aU=; b=eRTtkeH3NgJCjy1to2Uusv6Qp/ Nygkb915sQzycJJtLrfWs6aOhC3aNr0tQYVmu4VTcEJYz4xTMSEApRwPXmOJ2lzA Sheu2vj4jyFJC/z3vb6aiI1KrLbs0/mJbAZbqmM/UgukR4Yn8OUDIi11yB0Ig7LW HcGL/LG+d5XmfYOnCAA23ZhaLYIbRyVJ/nGFjUcC1912Y7izj1FO1YTxvZ59YAWr TbwfowaTngAr9LHF2qNEAQmvPJpHLILqmo8HNtfbipUSzV2wVvozEiBhIN9Haebo zpbIKm8kvHKF4nYqdNX0KvQzl3xUlMfzyXEm8Djg5WiQTPQkJR3Bksn+dNkQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:date:date:feedback-id :feedback-id:from:from:in-reply-to:in-reply-to:message-id :mime-version:references:reply-to:sender:subject:subject:to:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm1; t=1677514579; x=1677600979; bh=gyEHnWGhDfFt2Gu4gB/Bqdx54bxI G396QI5JbNzq7aU=; b=svhAJi84rKRyvhhozMBsXMvg6qI/GYqiFTpIKRvDAqjw n98CxMFl7OYokOoyd3J6H9j/ZiH2VTbvVAWwPaP60Z+J+Vsq+C3OYp0jGBCUAYdE k4GMSwzvx37hEv7e1kkI/mZXxwMjCbAk/tLowT0QBE3+hCQLImqMTsVT6En+tkyU bt1lMWLKwJ5J0FL5WKQ4cVLfJewGfzhn9B13flGAl2J2A+L2LZgBQcyO1CbjbJaC CCpMiweOeRQjqNEJG+Rvuqb29mAaXx9mZB6Cez4JZToCw+K41uKdDXtURBt3Sygq wrscnQxhqetCXiw14qA9gAsY5GLg4eWWYQu9TaUXBw== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedrudeltddgkeefucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepofgfggfkjghffffhvfevufgtsehttdertderredtnecuhfhrohhmpedftehr nhguuceuvghrghhmrghnnhdfuceorghrnhgusegrrhhnuggsrdguvgeqnecuggftrfgrth htvghrnhepffehueegteeihfegtefhjefgtdeugfegjeelheejueethfefgeeghfektdek teffnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomheprg hrnhgusegrrhhnuggsrdguvg X-ME-Proxy: Feedback-ID: i56a14606:Fastmail Received: by mailuser.nyi.internal (Postfix, from userid 501) id DC7AAB60086; Mon, 27 Feb 2023 11:16:18 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.9.0-alpha0-183-gbf7d00f500-fm-20230220.001-gbf7d00f5 Mime-Version: 1.0 Message-Id: In-Reply-To: <20230227155100.hhl4yvkyfqfyoa6h@CAB-WSD-L081021> References: <20230222115020.55867-1-avromanov@sberdevices.ru> <8e5f9bfa-d612-cd43-d722-d04c40938c62@linaro.org> <20230227142809.kujmrraf3pcdhqyn@CAB-WSD-L081021> <20230227155100.hhl4yvkyfqfyoa6h@CAB-WSD-L081021> Date: Mon, 27 Feb 2023 17:15:58 +0100 From: "Arnd Bergmann" To: "Dmitry Rokosov" Cc: "Neil Armstrong" , "Alexey Romanov" , "Rob Herring" , krzysztof.kozlowski+dt@linaro.org, "Kevin Hilman" , jbrunet@baylibre.com, martin.blumenstingl@googlemail.com, "Linus Walleij" , devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org, kernel@sberdevices.ru Subject: Re: [PATCH v1 0/3] Meson A1 32-bit support X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230227_081626_348208_4A25E042 X-CRM114-Status: GOOD ( 16.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Feb 27, 2023, at 16:51, Dmitry Rokosov wrote: > On Mon, Feb 27, 2023 at 03:58:50PM +0100, Arnd Bergmann wrote: >> >> I would argue that is a problem with buildroot, and using a 32-bit >> kernel is not something we should encourage over fixing buildroot >> to do it right, or building the kernel separately from the rootfs. >> >> We do allow building support for a couple of ARMv8 SoCs in 32-bit >> mode, but that is usually because they ship with a 32-bit bootrom >> and cannot actually run a 64-bit kernel. > > To be honest, I didn't know about this principle. It looks like a very > rational approach "start from max supported bitness". > Based on overall maintainers opinion, we have to prepare a patch for > buildroot to support compat mode :) That would be great, thanks a lot! For what it's worth, the main arguments in favor of running a 64-bit kernel with compat user space over a 32-bit kernel are support for: - larger RAM sizes without highmem (most 32-bit kernels only support 768MB of lowmem, and highmem sucks) - larger virtual address space (4GB vs 3GB or less) - CPU specific errata workarounds (arch/arm/ only has those for 32-bit cpus) - mitigations for common attacks such as spectre - security hardening that depends on larger address space (KASLR, BTI, ptrauth, PAN, ...) - emulating instructions that were removed in Armv8 (setend, swp, ...) Most of these don't apply in userspace, so the incentive to run smaller 32-bit userland on systems with less than 1GB of RAM usually outweighs the benefits of 64-bit userspace. Arnd _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel