From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f70.google.com (mail-lf0-f70.google.com [209.85.215.70]) by kanga.kvack.org (Postfix) with ESMTP id E87456B0005 for ; Sat, 10 Feb 2018 04:19:34 -0500 (EST) Received: by mail-lf0-f70.google.com with SMTP id p64so2980290lfe.12 for ; Sat, 10 Feb 2018 01:19:34 -0800 (PST) Received: from tartarus.angband.pl (tartarus.angband.pl. [89.206.35.136]) by mx.google.com with ESMTPS id l2si1470657ljb.252.2018.02.10.01.19.32 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 10 Feb 2018 01:19:33 -0800 (PST) Date: Sat, 10 Feb 2018 10:15:44 +0100 From: Adam Borowski Subject: Re: [PATCH 00/31 v2] PTI support for x86_32 Message-ID: <20180210091543.ynypx4y3koz44g7y@angband.pl> References: <1518168340-9392-1-git-send-email-joro@8bytes.org> <20180209191112.55zyjf4njum75brd@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180209191112.55zyjf4njum75brd@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Joerg Roedel Cc: Andy Lutomirski , Joerg Roedel , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , X86 ML , LKML , Linux-MM , Linus Torvalds , Dave Hansen , Josh Poimboeuf , Juergen Gross , Peter Zijlstra , Borislav Petkov , Jiri Kosina , Boris Ostrovsky , Brian Gerst , David Laight , Denys Vlasenko , Eduardo Valentin , Greg KH , Will Deacon , "Liguori, Anthony" , Daniel Gruss , Hugh Dickins , Kees Cook , Andrea Arcangeli , Waiman Long , Pavel Machek On Fri, Feb 09, 2018 at 08:11:12PM +0100, Joerg Roedel wrote: > On Fri, Feb 09, 2018 at 05:47:43PM +0000, Andy Lutomirski wrote: > > One thing worth noting is that performance of this whole series is > > going to be abysmal due to the complete lack of 32-bit PCID. Maybe > > any kernel built with this option set that runs on a CPU that has the > > PCID bit set in CPUID should print a big fat warning like "WARNING: > > you are using 32-bit PTI on a 64-bit PCID-capable CPU. Your > > performance will increase dramatically if you switch to a 64-bit > > kernel." > > Thanks for your review. I can add this warning, but I just hope that not > a lot of people will actually see it :) Alas, we got some data: https://popcon.debian.org/ says 20% of x86 users have i386 as their main ABI (current; people with popcon installed). Of those, 80% use 32-bit kernels: i686 881, x86_64 229, i586 14 (uname -m included in bug reports; data for 2016) -- and bug reporters tend to have more clue than the average user. There's no way so many folks still use pre-2004 computers. Thus, if you could include that big fat warning, distro developers would be thankful. Make it show fiery letters if you can. Preferably, we'd want a huge mallet reach out of the screen and bonk the user on the head, but with that impossible, a scary message would help. Let them use 32-bit userland, but if someone runs such a kernel on a modern machine, some kind of verbal abuse is warranted. Meow! -- ac?aGBP'a 3/4 a >>ac?aGBP|a ? aGBP 3/4 a ?ac?a ?a ?aGBP?a!? Vat kind uf sufficiently advanced technology iz dis!? ac?a!?a ?a .a ?a ?a ? -- Genghis Ht'rok'din a ?a 3aGBP?a ?a ?a ?a ? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org