From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [Xen-devel] [PATCH 3/3] xen: eliminate scalability issues from initial mapping setup Date: Thu, 4 Sep 2014 15:43:45 +0100 Message-ID: <54087AA1.8010208@citrix.com> References: <1409834326-29287-1-git-send-email-jgross@suse.com> <1409834326-29287-4-git-send-email-jgross@suse.com> <54086244.7020601@citrix.com> <540862FE.7070108@citrix.com> <540893F00200007800030E4F@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <540893F00200007800030E4F@mail.emea.novell.com> Sender: linux-kernel-owner@vger.kernel.org To: Jan Beulich Cc: David Vrabel , xen-devel@lists.xensource.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, Juergen Gross , linux-kernel@vger.kernel.org List-Id: xen-devel@lists.xenproject.org On 04/09/14 15:31, Jan Beulich wrote: >>>> On 04.09.14 at 15:02, wrote: >> On 04/09/14 13:59, David Vrabel wrote: >>> On 04/09/14 13:38, Juergen Gross wrote: >>>> Direct Xen to place the initial P->M table outside of the initial >>>> mapping, as otherwise the 1G (implementation) / 2G (theoretical) >>>> restriction on the size of the initial mapping limits the amount >>>> of memory a domain can be handed initially. >>> The three level p2m limits memory to 512 GiB on x86-64 but this patch >>> doesn't seem to address this limit and thus seems a bit useless to me. >> Any increase of the p2m beyond 3 levels will need to come with >> substantial libxc changes first. 3 level p2ms are hard coded throughout >> all the PV build and migrate code. > No, there no such dependency - the kernel could use 4 levels at > any time (sacrificing being able to get migrated), making sure it > only exposes the 3 levels hanging off the fourth level (or not > exposing this information at all) to external entities making this > wrong assumption. > > Jan > That would require that the PV kernel must start with a 3 level p2m and fudge things afterwards. At a minimum, I would expect a patch to libxc to detect a 4 level PV guest and fail with a meaningful error, rather than an obscure "m2p doesn't match p2m for mfn/pfn X". ~Andrew