Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753594AbcJKP7E (ORCPT ); Tue, 11 Oct 2016 11:59:04 -0400 Received: from mail-oi0-f53.google.com ([209.85.218.53]:35117 "EHLO mail-oi0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752818AbcJKP7D (ORCPT ); Tue, 11 Oct 2016 11:59:03 -0400 MIME-Version: 1.0 In-Reply-To: <57FCF26A02000078000F15E0@prv-mh.provo.novell.com> References: <20161010003523.4423-1-haozhong.zhang@intel.com> <57FCF26A02000078000F15E0@prv-mh.provo.novell.com> From: Dan Williams Date: Tue, 11 Oct 2016 08:53:33 -0700 Message-ID: Subject: Re: [Xen-devel] [RFC KERNEL PATCH 0/2] Add Dom0 NVDIMM support for Xen To: Jan Beulich Cc: andrew.cooper3@citrix.com, Stefano Stabellini , Arnd Bergmann , David Vrabel , Haozhong Zhang , Andrew Morton , Xiao Guangrong , Ross Zwisler , "linux-nvdimm@lists.01.org" , xen-devel@lists.xenproject.org, Boris Ostrovsky , Juergen Gross , Johannes Thumshirn , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1264 Lines: 23 On Tue, Oct 11, 2016 at 6:08 AM, Jan Beulich wrote: >>>> Andrew Cooper 10/10/16 6:44 PM >>> >>On 10/10/16 01:35, Haozhong Zhang wrote: >>> Xen hypervisor needs assistance from Dom0 Linux kernel for following tasks: >>> 1) Reserve an area on NVDIMM devices for Xen hypervisor to place >>> memory management data structures, i.e. frame table and M2P table. >>> 2) Report SPA ranges of NVDIMM devices and the reserved area to Xen >>> hypervisor. >> >>However, I can't see any justification for 1). Dom0 should not be >>involved in Xen's management of its own frame table and m2p. The mfns >>making up the pmem/pblk regions should be treated just like any other >>MMIO regions, and be handed wholesale to dom0 by default. > > That precludes the use as RAM extension, and I thought earlier rounds of > discussion had got everyone in agreement that at least for the pmem case > we will need some control data in Xen. The missing piece for me is why this reservation for control data needs to be done in the libnvdimm core? I would expect that any dax capable file could be mapped and made available to a guest. This includes /dev/ramX devices that are dax capable, but are external to the libnvdimm sub-system.