Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750944AbcKUFIi (ORCPT ); Mon, 21 Nov 2016 00:08:38 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36538 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744AbcKUFIf (ORCPT ); Mon, 21 Nov 2016 00:08:35 -0500 Date: Mon, 21 Nov 2016 00:08:30 -0500 From: Jerome Glisse To: Balbir Singh Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, John Hubbard , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" Subject: Re: [HMM v13 07/18] mm/ZONE_DEVICE/x86: add support for un-addressable device memory Message-ID: <20161121050829.GD7872@redhat.com> References: <1479493107-982-1-git-send-email-jglisse@redhat.com> <1479493107-982-8-git-send-email-jglisse@redhat.com> <33e9c941-ac57-3dfd-2ed9-c1d058a57d8f@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <33e9c941-ac57-3dfd-2ed9-c1d058a57d8f@gmail.com> User-Agent: Mutt/1.7.1 (2016-10-04) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 21 Nov 2016 05:08:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 965 Lines: 26 On Mon, Nov 21, 2016 at 01:08:56PM +1100, Balbir Singh wrote: > > > On 19/11/16 05:18, J?r?me Glisse wrote: > > It does not need much, just skip populating kernel linear mapping > > for range of un-addressable device memory (it is pick so that there > > is no physical memory resource overlapping it). All the logic is in > > share mm code. > > > > Only support x86-64 as this feature doesn't make much sense with > > constrained virtual address space of 32bits architecture. > > > > Is there a reason this would not work on powerpc64 for example? > Could you document the limitations -- testing/APIs/missing features? It should be straight forward for powerpc64, i haven't done it but i certainly can try to get access to some powerpc64 and add support for it. The only thing to do is to avoid creating kernel linear mapping for the un-addressable memory (just for safety reasons we do not want any read/ write to invalid physical address). Cheers, J?r?me