From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: 32-bit PV guests and 168 GB boundary Date: Mon, 15 Apr 2013 15:51:23 +0100 Message-ID: <516C13EB.4050209@citrix.com> References: <516C0CD1.90403@linode.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <516C0CD1.90403@linode.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: Nick Pegg Cc: "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 15/04/13 15:21, Nick Pegg wrote: > Hello, > > I've recently ran into a problem on a physical machine with a large > amount of memory where 32-bit PV guests would refuse to boot with this > error message: > > xm create: Error: (4, 'Out of memory', "panic: xc_dom_boot.c:159: > xc_dom_boot_mem_init: can't allocate low memory for domain") > > We discovered that there's a boundary where 32-bit PV guests can't be > allocated memory above 168GB, along with the work-around config option > to reserve memory for these guests (total_available_memory in > xend-config.sxp). > > Could someone clarify why this is a restriction? Is this some sort of > hardware limitation? > > > Thanks, > Nick This is because of the amount of the Xen m2p table mapped into 32bit kernel space, between 0xf5800000 and 0xffffffff. PV guests require the m2p table to perform paravirtualised memory management. This is a fundamental limit of 32bit PV guests. ~Andrew > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel