From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C087C10F05 for ; Thu, 4 Apr 2019 05:03:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 33A4520700 for ; Thu, 4 Apr 2019 05:03:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726783AbfDDFD1 (ORCPT ); Thu, 4 Apr 2019 01:03:27 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:51648 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726511AbfDDFDY (ORCPT ); Thu, 4 Apr 2019 01:03:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 496C7A78; Wed, 3 Apr 2019 22:03:24 -0700 (PDT) Received: from [10.162.40.100] (p8cg001049571a15.blr.arm.com [10.162.40.100]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 182453F557; Wed, 3 Apr 2019 22:03:17 -0700 (PDT) Subject: Re: [PATCH 6/6] arm64/mm: Enable ZONE_DEVICE To: Jerome Glisse , Robin Murphy Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, akpm@linux-foundation.org, will.deacon@arm.com, catalin.marinas@arm.com, mhocko@suse.com, mgorman@techsingularity.net, james.morse@arm.com, mark.rutland@arm.com, cpandya@codeaurora.org, arunks@codeaurora.org, dan.j.williams@intel.com, osalvador@suse.de, logang@deltatee.com, david@redhat.com, cai@lca.pw References: <1554265806-11501-1-git-send-email-anshuman.khandual@arm.com> <1554265806-11501-7-git-send-email-anshuman.khandual@arm.com> <20190403160722.GB12818@redhat.com> From: Anshuman Khandual Message-ID: <4507c5b0-0a96-6e28-d98c-06e3a696551c@arm.com> Date: Thu, 4 Apr 2019 10:33:19 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190403160722.GB12818@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/03/2019 09:37 PM, Jerome Glisse wrote: > On Wed, Apr 03, 2019 at 02:58:28PM +0100, Robin Murphy wrote: >> [ +Dan, Jerome ] >> >> On 03/04/2019 05:30, Anshuman Khandual wrote: >>> Arch implementation for functions which create or destroy vmemmap mapping >>> (vmemmap_populate, vmemmap_free) can comprehend and allocate from inside >>> device memory range through driver provided vmem_altmap structure which >>> fulfils all requirements to enable ZONE_DEVICE on the platform. Hence just >> >> ZONE_DEVICE is about more than just altmap support, no? >> >>> enable ZONE_DEVICE by subscribing to ARCH_HAS_ZONE_DEVICE. But this is only >>> applicable for ARM64_4K_PAGES (ARM64_SWAPPER_USES_SECTION_MAPS) only which >>> creates vmemmap section mappings and utilize vmem_altmap structure. >> >> What prevents it from working with other page sizes? One of the foremost >> use-cases for our 52-bit VA/PA support is to enable mapping large quantities >> of persistent memory, so we really do need this for 64K pages too. FWIW, it >> appears not to be an issue for PowerPC. >> >>> Signed-off-by: Anshuman Khandual >>> --- >>> arch/arm64/Kconfig | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >>> index db3e625..b5d8cf5 100644 >>> --- a/arch/arm64/Kconfig >>> +++ b/arch/arm64/Kconfig >>> @@ -31,6 +31,7 @@ config ARM64 >>> select ARCH_HAS_SYSCALL_WRAPPER >>> select ARCH_HAS_TEARDOWN_DMA_OPS if IOMMU_SUPPORT >>> select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST >>> + select ARCH_HAS_ZONE_DEVICE if ARM64_4K_PAGES >> >> IIRC certain configurations (HMM?) don't even build if you just turn this on >> alone (although of course things may have changed elsewhere in the meantime) >> - crucially, though, from previous discussions[1] it seems fundamentally >> unsafe, since I don't think we can guarantee that nobody will touch the >> corners of ZONE_DEVICE that also require pte_devmap in order not to go >> subtly wrong. I did get as far as cooking up some patches to sort that out >> [2][3] which I never got round to posting for their own sake, so please >> consider picking those up as part of this series. > > Correct _do not_ enable ZONE_DEVICE without support for pte_devmap detection. Driver managed ZONE_DEVICE memory which never maps into user page table is not a valid use case for ZONE_DEVICE ? Also what about MEMORY_DEVICE_PRIVATE ? That can never be mapped into user page table. A driver can still manage these non coherent memory through it's struct pages (which will be allocated inside RAM) > If you want some feature of ZONE_DEVICE. Like HMM as while DAX does require > pte_devmap, HMM device private does not. So you would first have to split > ZONE_DEVICE into more sub-features kconfig option. CONFIG_ZONE_DEVICE does not do that already ! All it says is that a device memory range can be plugged into ZONE_DEVICE either as PRIVATE (non-coherent) or PUBLIC/PCI_P2PDMA (coherent) memory without mandating anything about how these memory will be further used. > > What is the end use case you are looking for ? Persistent memory ? Persistent memory is one of the primary use cases.