From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752776AbXCEMtY (ORCPT ); Mon, 5 Mar 2007 07:49:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932344AbXCEMtX (ORCPT ); Mon, 5 Mar 2007 07:49:23 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:45785 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752773AbXCEMtX (ORCPT ); Mon, 5 Mar 2007 07:49:23 -0500 Date: Mon, 5 Mar 2007 13:40:24 +0100 From: Ingo Molnar To: Avi Kivity Cc: Andrew Morton , Linus Torvalds , linux-kernel@vger.kernel.org, Roland McGrath , Andi Kleen , Rusty Russell Subject: Re: [patch] paravirt: VDSO page is essential Message-ID: <20070305124024.GA19338@elte.hu> References: <20070305120631.GA14105@elte.hu> <45EC0EB7.7080300@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45EC0EB7.7080300@qumranet.com> User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.0.3 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Avi Kivity wrote: > >-#ifdef CONFIG_PARAVIRT > >-unsigned int __read_mostly vdso_enabled = 0; > >-#else > > unsigned int __read_mostly vdso_enabled = 1; > >-#endif > Can't paravirt patch the syscall instruction like it does the rest of > the kernel? we want to keep the guest as simple and unmodified as possible. And all this #ifdef jungle /will/ bite back. Especially if the change goes in with zero explanation like it did: [PATCH] paravirt: Disable vdso by default when CONFIG_PARAVIRT is enabled They don't work together and this way even glibc still works. i rather want an experimental feature (CONFIG_PARAVIRT) broken on some hypervisors for a bit than an entire body of guest OSs getting used to the "you dont have to deal with this VDSO annoyance by default" quirk forever ... but yes, i agree that the hypervisor should have the ability to patch the syscall instruction of both the hypervisor interface and of the VDSO interface. But this wasnt implemented like that, and the #ifdef quirk just /prevents/ a sane solution like that from ever getting done the right way. Ingo