From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755991Ab1HWTQv (ORCPT ); Tue, 23 Aug 2011 15:16:51 -0400 Received: from terminus.zytor.com ([198.137.202.10]:49371 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751791Ab1HWTQo (ORCPT ); Tue, 23 Aug 2011 15:16:44 -0400 Message-ID: <4E53FC6E.1030807@zytor.com> Date: Tue, 23 Aug 2011 12:15:58 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0 MIME-Version: 1.0 To: Borislav Petkov CC: Andrew Lutomirski , Linus Torvalds , Al Viro , Ingo Molnar , "user-mode-linux-devel@lists.sourceforge.net" , Richard Weinberger , "linux-kernel@vger.kernel.org" , "mingo@redhat.com" Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386) References: <20110823000314.GW2203@ZenIV.linux.org.uk> <4E52EF2A.8060608@zytor.com> <20110823010146.GY2203@ZenIV.linux.org.uk> <20110823011312.GZ2203@ZenIV.linux.org.uk> <20110823021717.GA2203@ZenIV.linux.org.uk> <20110823061531.GC2203@ZenIV.linux.org.uk> <20110823162251.GC13138@aftab> In-Reply-To: <20110823162251.GC13138@aftab> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/23/2011 09:22 AM, Borislav Petkov wrote: > On Tue, Aug 23, 2011 at 12:11:43PM -0400, Andrew Lutomirski wrote: >> In any case, this seems insanely overcomplicated. I'd be less afraid >> of something like my approach (which, I think, makes all of the >> SYSCALL weirdness pretty much transparent to ptrace users) or of just >> removing SYSCALL entirely from 32-bit code. > > I don't think that removing SYSCALL from 32-bit code just so that UML > trapped syscalls work is something we'd like since SYSCALL is much > cheaper than INT $0x80: > > "As a result, SYSCALL and SYSRET can take fewer than one-fourth the > number of internal clock cycles to complete than the legacy CALL and RET > instructions." > > http://support.amd.com/us/Processor_TechDocs/24593.pdf, p. 152. > > I know, it is 32-bit syscall on 64-bit kernel which should be pretty > rare but still... > Right, but if you had said the difference had disappeared on current AMD silicon it would be much less of an issue. That's why I wanted to find that bit out from you. -hpa