Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754801AbbGJQfj (ORCPT ); Fri, 10 Jul 2015 12:35:39 -0400 Received: from mail-ie0-f181.google.com ([209.85.223.181]:34645 "EHLO mail-ie0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754662AbbGJQfe (ORCPT ); Fri, 10 Jul 2015 12:35:34 -0400 MIME-Version: 1.0 In-Reply-To: References: <23d4709cee2fe92c32d41b99c7a3c1823725925a.1436312944.git.luto@kernel.org> <559C8BFE.6050604@linux.intel.com> <87twtc14po.fsf@x220.int.ebiederm.org> Date: Fri, 10 Jul 2015 09:35:34 -0700 X-Google-Sender-Auth: 6PHPhVk-ItNQJP45XswT2DbMCTs Message-ID: Subject: Re: [PATCH] x86/kconfig/32: Mark CONFIG_VM86 as BROKEN From: Linus Torvalds To: Andy Lutomirski Cc: "Eric W. Biederman" , Arjan van de Ven , Andy Lutomirski , "the arch/x86 maintainers" , Linux Kernel Mailing List , Oleg Nesterov , Kees Cook , Peter Zijlstra , Borislav Petkov Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1408 Lines: 31 On Fri, Jul 10, 2015 at 7:37 AM, Andy Lutomirski wrote: > > Having just written a pile of tests for it, I don't think so, as long as none > of the syscall slow path stuff is in use :( It seems that you are thinking that people actually use vm86 mode as a real Linux mode, and do system calls from it etc. I'm sure that has happened in some crazy situation (people doing some random pseudo-BIOS etc), but it's not the common situation at all. The common situation is that you enter vm86 mode with vm86(), and that you exit it due to one of the (many) unhandled situations or a signal or whatever. Yeah,we handle a few sad instructions directly, but most vm86 exits just return to user mode. The system call paths just aren't an issue in reality, because they just aren't used. And I'm personally violently against Ingo's idea of emulating this with an instruction emulator. Hell no. That's what user mode does, and it's fine there. In the kernel, we either support the hardware vm86 mode, or we phase it out because we can show that nobody uses it any more. None of that "let's emulate it in software" crud. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/