From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [patch] paravirt: VDSO page is essential Date: Mon, 5 Mar 2007 21:16:42 +0100 Message-ID: <200703052116.42807.ak@suse.de> References: <20070305120631.GA14105@elte.hu> <20070305143437.GF22829@bingen.suse.de> <45EC796D.5050705@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <45EC796D.5050705@vmware.com> Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Zachary Amsden Cc: Rusty Russell , Ingo Molnar , Andrew Morton , linux-kernel@vger.kernel.org, Roland McGrath , virtualization List-Id: virtualization@lists.linuxfoundation.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