From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCHv1] xen/balloon: disable memory hotplug in PV guests Date: Mon, 9 Mar 2015 15:31:30 +0000 Message-ID: <54FDBCD2.8040807@citrix.com> References: <1425910200-17541-1-git-send-email-david.vrabel@citrix.com> <54FDB7B8.7000305@oracle.com> <54FDB8A4.9020904@citrix.com> <54FDBB53.7070108@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YUzea-0001Qm-Gv for xen-devel@lists.xenproject.org; Mon, 09 Mar 2015 15:31:36 +0000 In-Reply-To: <54FDBB53.7070108@oracle.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: Boris Ostrovsky , xen-devel@lists.xenproject.org Cc: Daniel Kiper List-Id: xen-devel@lists.xenproject.org On 09/03/15 15:25, Boris Ostrovsky wrote: > On 03/09/2015 11:13 AM, David Vrabel wrote: >> On 09/03/15 15:09, Boris Ostrovsky wrote: >>> On 03/09/2015 10:10 AM, David Vrabel wrote: >>>> Memory hotplug doesn't work with PV guests because: >>>> >>>> a) The p2m cannot be expanded to cover the new sections. >>>> >>>> b) add_memory() builds page tables for the new sections which means >>>> the new pages must have valid p2m entries (or a BUG occurs). >>> Is this due to recent p2m rework? >> (a) is but (b) has always meant memory hotplug on PV was broken. > > I can see why (b) should probably have prevented it from working but I > tried this on 4.4/3.17 and that seemed to work (it indeed does not > function well on newer bits). I tried it on 3.10 (+ some other bits and pieces) and it was definitely broken for reason (b). I had to refactor the balloon driver to populate the sections before calling add_memory() before it would work. But this can't be done now because of (a). David