From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753880AbaH2O4O (ORCPT ); Fri, 29 Aug 2014 10:56:14 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:50161 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752528AbaH2O4N (ORCPT ); Fri, 29 Aug 2014 10:56:13 -0400 Date: Fri, 29 Aug 2014 10:55:58 -0400 From: Konrad Rzeszutek Wilk To: Jan Beulich Cc: Stefan Bader , Kees Cook , David Vrabel , "xen-devel@lists.xensource.com" , Linux Kernel Mailing List Subject: Re: [Xen-devel] [PATCH] Solved the Xen PV/KASLR riddle Message-ID: <20140829145558.GK3609@laptop.dumpdata.com> References: <20140827204940.GA10556@laptop.dumpdata.com> <1409248903-19625-1-git-send-email-stefan.bader@canonical.com> <20140829140823.GF3609@laptop.dumpdata.com> <54008DDA.3040701@canonical.com> <5400ADD6020000780002F159@mail.emea.novell.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5400ADD6020000780002F159@mail.emea.novell.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 29, 2014 at 03:44:06PM +0100, Jan Beulich wrote: > >>> On 29.08.14 at 16:27, wrote: > > Sure. Btw, someone also contacted me saying they have the same problem > > without > > changing the layout but having really big initrd (500M). While that feels > > like > > it should be impossible (if the kernel+initrd+xen stuff has to fix the 512M > > kernel image size area then). But if it can happen, then surely it does > > cause > > mappings to be where the module space starts then. > > Since the initrd doesn't really need to be mapped into the (limited) > virtual address space a pv guest starts with, we specifically got > > /* > * Whether or not the guest can deal with being passed an initrd not > * mapped through its initial page tables. > */ > #define XEN_ELFNOTE_MOD_START_PFN 16 > > to deal with that situation. The hypervisor side for Dom0 is in place, > and the kernel side works in our (classic) kernels. Whether it got > implemented for DomU meanwhile I don't know; I'm pretty certain > pv-ops kernels don't support it so far. Correct - Not implemented. Here is what I had mentioned in the past: (see http://lists.xen.org/archives/html/xen-devel/2014-03/msg00580.html) XEN_ELFNOTE_INIT_P2M, XEN_ELFNOTE_MOD_START_PFN - I had been looking at that but I can't figure out a nice way of implementing this without the usage of SPARSEMAP_VMAP virtual addresses - which is how the classic Xen does it. But then - I don't know who is using huge PV guests - as the PVHVM does a fine job? But then with PVH, now you can boot with large amount of memory (1TB?) - so some of these issues would go away? Except the 'large ramdisk' as that would eat in the MODULES_VADDR I think? Needs more thinking. .. and then I left it and to my suprise saw on Luis's slides that Jurgen is going to take a look at that (500GB support). > > Jan >