From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753601Ab1E0MLA (ORCPT ); Fri, 27 May 2011 08:11:00 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:33006 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753068Ab1E0MK5 convert rfc822-to-8bit (ORCPT ); Fri, 27 May 2011 08:10:57 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=K+L6ufMyytV+uaesck2xvW5bf7MZ9AO8DmKObvpikUUqa6teMy5aIp88fFABLGW5i1 wQUhC+v1uGCoQSIhBg2ze8jTsJx/jqHfW6GVHOgT/UOvDfe2qoIa9P25cZF/TTui9spu lxnk9G1jle6e0KBhg+VjA7taHBIIOTKWO+XLY= MIME-Version: 1.0 In-Reply-To: References: <4DDEC589.3010201@mit.edu> <20110527061208.GB9260@elte.hu> From: Andrew Lutomirski Date: Fri, 27 May 2011 08:10:37 -0400 X-Google-Sender-Auth: qD6yVe5DwPmmf2hoRvWcvmkP5Zo Message-ID: Subject: Re: [GIT pull] x86 vdso updates To: richard -rw- weinberger Cc: Ingo Molnar , Thomas Gleixner , Linus Torvalds , Andrew Morton , x86@kernel.org, LKML Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 27, 2011 at 7:59 AM, richard -rw- weinberger wrote: > On Fri, May 27, 2011 at 1:36 PM, Andrew Lutomirski wrote: >> 2. Remove the vsyscall64 sysctl.  That will reduce the number of >> vsyscalls that require the kernel's help to one.  (This is a bit >> unfortunate for UML users, but I'm not sure what to do about that. >> UML vgetcpu is already terminally broken.) > > Can you please be a bit more precise on that? > When there is anything I can do, let me know... glibc's implementation of time, sched_getcpu, and (for static binaries) gettimeofday calls a fixed address in kernel space which returns the answer. On UML, that address is presumably in *host* kernel space and the host will return what the host thinks the answer is. That's a bit unfortunate if the guest has a different idea of cpu numbering or what time it is. Right now, setting kernel.vsyscall64=0 will turn gettimeofday and time (but not sched_getcpu) into a real syscall. The problem is that I want to remove the vsyscall64 sysctl. If this is considered enough of a regression, then I guess we can leave vsyscall64 around for awhile, but it will require extra work in the soon-to-be syscall emulation hack to make sure that UML can still trap the syscall. The real solution is to fix glibc to use the vDSO which should avoid this problem entirely. --Andy > > -- > Thanks, > //richard >