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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ECD09C433DB for ; Sun, 28 Mar 2021 06:19:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC2C661968 for ; Sun, 28 Mar 2021 06:19:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230487AbhC1GTU (ORCPT ); Sun, 28 Mar 2021 02:19:20 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:50928 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229577AbhC1GS4 (ORCPT ); Sun, 28 Mar 2021 02:18:56 -0400 Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 12S6IbCV022735; Sun, 28 Mar 2021 08:18:37 +0200 Date: Sun, 28 Mar 2021 08:18:37 +0200 From: Willy Tarreau To: Thomas Gleixner Cc: Mateusz Jonczyk , linux-kernel@vger.kernel.org Subject: Re: Testers wanted: Atom netbooks with x86_64 disabled by BIOS Message-ID: <20210328061837.GA22710@1wt.eu> References: <20210327203218.119372-1-mat.jonczyk@o2.pl> <20210327211322.121708-1-mat.jonczyk@o2.pl> <20210327232551.GA20783@1wt.eu> <87lfa8cchf.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87lfa8cchf.ffs@nanos.tec.linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thomas, On Sun, Mar 28, 2021 at 03:07:24AM +0200, Thomas Gleixner wrote: > On Sun, Mar 28 2021 at 00:25, Willy Tarreau wrote: > > On Sat, Mar 27, 2021 at 10:13:22PM +0100, Mateusz Jonczyk wrote: > > FWIW I tested on my ASUS 1025C which runs on an Atom N2600 forced to > > 32-bit. I had already tried in the past but wanted to give it a try > > again in case I'd have missed anything. Sadly it didn't work, I'm > > still getting the "requires an x86-64 CPU" message. > > > > Given these machines were really cheap, I've always suspected that they > > employ cheaper, low-grade CPUs, possibly having been subject to reduced > > tests where x86_64-specific parts were not even verified and might be > > defective. This may explain why they forcefully disable long mode there, > > but that's just speculation. > > There are some of these '32bit only' CPUs out there in the wild which > actually support long mode. Some of them even do not have the long mode > CPUID bit fused out. Yes, I'm aware of this as well. We might even have talked to the same "victim" :-) > But whether it works is a different story: > > - If the CPUID bit is on, then the chance is high, but it runs out of > spec (guarantee wise) > > - If it's off is still might work by some definition of work as they > might have fused off more or there are actual defects in some 64bit > only area which are irrelevant when in 32bit mode. > > Even if it could work perfectly fine, the BIOS/SMM/ucode can prevent > switching to long mode. > > It's a lost cause. I agree. While I bought this netbook to have a 64-bit CPU and was extremely disappointed, after seeing that it was not just a matter of "oops we forgot to enable LM", I concluded that it was pointless to try to go further, as I would never trust it anyway. Cheers, Willy