From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [Xen-devel] [PATCH] Solved the Xen PV/KASLR riddle Date: Mon, 01 Sep 2014 06:03:06 +0200 Message-ID: <5403EFFA.50701@suse.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> <20140829145558.GK3609@laptop.dumpdata.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140829145558.GK3609@laptop.dumpdata.com> Sender: linux-kernel-owner@vger.kernel.org To: Konrad Rzeszutek Wilk , Jan Beulich Cc: Linux Kernel Mailing List , "xen-devel@lists.xensource.com" , Kees Cook , Stefan Bader , David Vrabel List-Id: xen-devel@lists.xenproject.org On 08/29/2014 04:55 PM, Konrad Rzeszutek Wilk wrote: > 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). I have a patch which should do the job. It is based on the classic kernel patch Jan mentioned above. The system is coming up with it, I haven't tested it with a huge initrd up to now. My plan was to post the patch together with the rest of the >500GB support, but I can send it on it's own if required. Juergen