From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752850AbXCEURz (ORCPT ); Mon, 5 Mar 2007 15:17:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752851AbXCEURy (ORCPT ); Mon, 5 Mar 2007 15:17:54 -0500 Received: from cantor2.suse.de ([195.135.220.15]:50074 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752850AbXCEURy (ORCPT ); Mon, 5 Mar 2007 15:17:54 -0500 From: Andi Kleen Organization: SUSE Linux Products GmbH, Nuernberg, GF: Markus Rex, HRB 16746 (AG Nuernberg) To: Zachary Amsden Subject: Re: [patch] paravirt: VDSO page is essential Date: Mon, 5 Mar 2007 21:16:42 +0100 User-Agent: KMail/1.9.5 Cc: Rusty Russell , Ingo Molnar , Andrew Morton , linux-kernel@vger.kernel.org, Roland McGrath , virtualization References: <20070305120631.GA14105@elte.hu> <20070305143437.GF22829@bingen.suse.de> <45EC796D.5050705@vmware.com> In-Reply-To: <45EC796D.5050705@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200703052116.42807.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org We are not concerned so much > with supporting legacy user land deployments, I am concerned about that. I won't merge any patches that break compatibility by default. > > What would probably work is to somehow decide at runtime if a hypervisor > > is there or not and then set vdso default based on that. I guess that > > detection would be hypervisor specific though and probably would > > need paravirt ops extensions. > > > > What we really need to do is to be able to detect an old user land and > drop VDSO support when that is found. Rusty implemented that, but it was widely considered too ugly (and it was not 100% reliable e.g. with chroots) > But since we can't do that, the > next best thing is to allow the hypervisor to choose whatever workaround > it wants when it moves the fixmap and compat_vdso was enabled. In our > case, the workaround we will want is a boot option to disable VDSO for > old user land, The boot option is already there, but boot options for is not my idea of user friendly binary compatibility. > and a printk warning if you take #GPs and kill the init > proc, because for us, this is not an expected support scenario. We > would much rather support the VDSO by default in paravirt kernels even > with COMPAT_VDSO turned on. But you can't have it at the compatible fixed address, right? -Andi