From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH v3 27/32] libxc: change the position of the special pages Date: Fri, 10 Jul 2015 15:06:14 -0400 Message-ID: <20150710190614.GF30788@l.oracle.com> References: <1435923310-9019-1-git-send-email-roger.pau@citrix.com> <1435923310-9019-28-git-send-email-roger.pau@citrix.com> <5596ABEF.9010004@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1ZDdcu-00054F-CV for xen-devel@lists.xenproject.org; Fri, 10 Jul 2015 19:06:24 +0000 Content-Disposition: inline In-Reply-To: <5596ABEF.9010004@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Roger Pau =?iso-8859-1?Q?Monn=E9?= Cc: xen-devel@lists.xenproject.org, Stefano Stabellini , Wei Liu , Ian Jackson , Ian Campbell List-Id: xen-devel@lists.xenproject.org On Fri, Jul 03, 2015 at 05:36:15PM +0200, Roger Pau Monn=E9 wrote: > El 03/07/15 a les 13.35, Roger Pau Monne ha escrit: > > Change the physical memory address of the special pages when there are = no > > emulated devices. On HVM guests the special pages have always been rese= rved > > so that they end at the 0xff000 pfn, but there are some problems with t= his > > approach when used without emulated devices: > > = > > - If we want to allow HVMlite to be used for Dom0 those special pages > > cannot be placed inside of the MMIO hole or else they may clash with= MMIO > > regions of physical devices passed-through to Dom0. > > - If there's no emulated devices the guests needs to access the console > > page and the command line very early during boot. This is a problem = for > > FreeBSD at least, since the early page tables only map memory up to = 1GiB. > > = > > So instead append the special pages after the kernel and ramdisk. The g= uest > > must make sure it figures out the position of those pages very early du= ring > > boot, since the region is not marked as reserved in the memory map. > = > After thinking a little bit about this, I don't think this is the right > solution. Placing all the special pages after the kernel/ramdisk will > make it quite hard to use bootloaders like pvgrub inside of HVMlite > guests. I will see if I can come up with a better way to solve this, > comments welcome. Could stick at the start of memory, mark it as E820_RESV or such. Or at 16MB or such? > = > Roger. > = > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel