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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D240DC433EF for ; Sun, 24 Jul 2022 12:34:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236791AbiGXMbG (ORCPT ); Sun, 24 Jul 2022 08:31:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231669AbiGXMay (ORCPT ); Sun, 24 Jul 2022 08:30:54 -0400 Received: from tartarus.angband.pl (tartarus.angband.pl [51.83.246.204]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63E083885 for ; Sun, 24 Jul 2022 05:30:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=angband.pl; s=tartarus; h=In-Reply-To:Content-Transfer-Encoding:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=gwguV63Fi5fB1wTTDHlqLIZrWqWY7WfW5nfc8u5bpKE=; b=n+AHe5UDeDKrM/fd/enGiSzNMm /eDSjcjG1KNoElE0QsCBsi2ZIZPxdBi79IFCNycHaXAJRqFgTH3spmA5ukxnQPwDwBOyKgAas+pin 0mU1M377EDShpHU7eK76Ixx4WflY7lnO5Vt5yTZ0FVCun1PDlpQrJ0JcrrzXBn7DMhL8=; Received: from kilobyte by tartarus.angband.pl with local (Exim 4.94.2) (envelope-from ) id 1oFake-004e7X-9V; Sun, 24 Jul 2022 14:30:28 +0200 Date: Sun, 24 Jul 2022 14:30:28 +0200 From: Adam Borowski To: Jan Engelhardt Cc: Greg Kroah-Hartman , Naresh Kamboju , open list , X86 ML , lkft-triage@lists.linaro.org, Borislav Petkov , Pawan Gupta , Peter Zijlstra , Josh Poimboeuf Subject: Re: RETBleed: WARNING: Spectre v2 mitigation leaves CPU vulnerable to RETBleed attacks, data leaks possible! Message-ID: References: <3139s0q2-2o3s-4334-o670-n3p223o34ps9@vanv.qr> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3139s0q2-2o3s-4334-o670-n3p223o34ps9@vanv.qr> X-Junkbait: aaron@angband.pl, zzyx@angband.pl X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: kilobyte@angband.pl X-SA-Exim-Scanned: No (on tartarus.angband.pl); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 24, 2022 at 11:25:04AM +0200, Jan Engelhardt wrote: > On Saturday 2022-07-23 23:50, Adam Borowski wrote: > >> > We are booting the i386 kernel on an x86 machine. > > > >[..] And for quite some tasks, halved word > >size (thus ~2/3 memory usage) can overcome register starvation and win > >benchmarks. > > So how many benchmarks does a 32-bit userspace with a 32-bit kernel > win over 32-bit userspace with a 64-bit kernel? Likely none or almost none. What we want is for people to run 64-bit kernel, there are no real issues with userland. Valid uses to run 32-bit kernel: * ancient hardware (so much more prevalent than m68k we support!; non-hobbyists should upgrade to reduce power costs) * hardware to run that 100$k-1M ISA industrial control/medical imaging card (which, having ISA, is necessarily ancient too) * us devs testing the above Only the last case will have a modern CPU, thus requiring an explicit override won't hurt less educated users -- while telling the latter to grab a 64-bit kernel if their hardware isn't ancient would have other benefits for them beside just vulnerabilities. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ Aryans: split from other Indo-Europeans ~2900-2000BC → Ural → ⣾⠁⢠⠒⠀⣿⡁ Bactria → settled 2000-1000BC in northwest India. ⢿⡄⠘⠷⠚⠋⠀ Gypsies: came ~1000AD from northern India; aryan. ⠈⠳⣄⠀⠀⠀⠀ Germans: IE people who came ~2800BC to Scandinavia; not aryan.