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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 9BB64C04A6B for ; Wed, 8 May 2019 20:27:18 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5FA7B2173C for ; Wed, 8 May 2019 20:27:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5FA7B2173C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:43459 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOT9p-0007ZK-Gk for qemu-devel@archiver.kernel.org; Wed, 08 May 2019 16:27:17 -0400 Received: from eggs.gnu.org ([209.51.188.92]:48757) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOT8z-00077h-Sy for qemu-devel@nongnu.org; Wed, 08 May 2019 16:26:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOT8y-0005Ei-EH for qemu-devel@nongnu.org; Wed, 08 May 2019 16:26:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37160) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOT8u-0005Bf-Vn; Wed, 08 May 2019 16:26:21 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BBB083083391; Wed, 8 May 2019 20:26:19 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-120-255.rdu2.redhat.com [10.10.120.255]) by smtp.corp.redhat.com (Postfix) with ESMTP id 99F891001DDD; Wed, 8 May 2019 20:26:13 +0000 (UTC) To: Robin Murphy , Shameerali Kolothum Thodi , "will.deacon@arm.com" , Catalin Marinas , Anshuman Khandual , "linux-arm-kernel@lists.infradead.org" , linux-mm References: <5FC3163CFD30C246ABAA99954A238FA83F1B6A66@lhreml524-mbs.china.huawei.com> From: Laszlo Ersek Message-ID: <190831a5-297d-addb-ea56-645afb169efb@redhat.com> Date: Wed, 8 May 2019 22:26:12 +0200 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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Wed, 08 May 2019 20:26:20 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [Question] Memory hotplug clarification for Qemu ARM/virt X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "peter.maydell@linaro.org" , "ard.biesheuvel@linaro.org" , Linuxarm , "qemu-devel@nongnu.org" , "eric.auger@redhat.com" , "qemu-arm@nongnu.org" , "xuwei \(O\)" , Jonathan Cameron , Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 05/08/19 14:50, Robin Murphy wrote: > Hi Shameer, >=20 > On 08/05/2019 11:15, Shameerali Kolothum Thodi wrote: >> Hi, >> >> This series here[0] attempts to add support for PCDIMM in QEMU for >> ARM/Virt platform and has stumbled upon an issue as it is not clear(at >> least >> from Qemu/EDK2 point of view) how in physical world the hotpluggable >> memory is handled by kernel. >> >> The proposed implementation in Qemu, builds the SRAT and DSDT parts >> and uses GED device to trigger the hotplug. This works fine. >> >> But when we added the DT node corresponding to the PCDIMM(cold plug >> scenario), we noticed that Guest kernel see this memory during early b= oot >> even if we are booting with ACPI. Because of this, hotpluggable memory >> may end up in zone normal and make it non-hot-un-pluggable even if Gue= st >> boots with ACPI. >> >> Further discussions[1] revealed that, EDK2 UEFI has no means to >> interpret the >> ACPI content from Qemu(this is designed to do so) and uses DT info to >> build the GetMemoryMap(). To solve this, introduced "hotpluggable" >> property >> to DT memory node(patches #7 & #8 from [0]) so that UEFI can >> differentiate >> the nodes and exclude the hotpluggable ones from GetMemoryMap(). >> >> But then Laszlo rightly pointed out that in order to accommodate the >> changes >> into UEFI we need to know how exactly Linux expects/handles all the >> hotpluggable memory scenarios. Please find the discussion here[2]. >> >> For ease, I am just copying the relevant comment from Laszlo below, >> >> /****** >> "Given patches #7 and #8, as I understand them, the firmware cannot >> distinguish >> =C2=A0 hotpluggable & present, from hotpluggable & absent. The firmwar= e can >> only >> =C2=A0 skip both hotpluggable cases. That's fine in that the firmware = will >> hog neither >> =C2=A0 type -- but is that OK for the OS as well, for both ACPI boot a= nd DT >> boot? >> >> Consider in particular the "hotpluggable & present, ACPI boot" case. >> Assuming >> we modify the firmware to skip "hotpluggable" altogether, the UEFI mem= map >> will not include the range despite it being present at boot. >> Presumably, ACPI >> will refer to the range somehow, however. Will that not confuse the OS= ? >> >> When Igor raised this earlier, I suggested that >> hotpluggable-and-present should >> be added by the firmware, but also allocated immediately, as >> EfiBootServicesData >> type memory. This will prevent other drivers in the firmware from >> allocating AcpiNVS >> or Reserved chunks from the same memory range, the UEFI memmap will >> contain >> the range as EfiBootServicesData, and then the OS can release that >> allocation in >> one go early during boot. >> >> But this really has to be clarified from the Linux kernel's >> expectations. Please >> formalize all of the following cases: >> >> OS boot (DT/ACPI)=C2=A0 hotpluggable & ...=C2=A0 GetMemoryMap() should= report >> as=C2=A0 DT/ACPI should report as >> -----------------=C2=A0 ------------------=C2=A0 >> -------------------------------=C2=A0 ------------------------ >> DT=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 present=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ?=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 = ? >> DT=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 absent=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ?=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0 ? >> ACPI=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 present=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0 ?=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ? >> ACPI=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 absent=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ?=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ? >> >> Again, this table is dictated by Linux." >> >> ******/ >> >> Could you please take a look at this and let us know what is expected >> here from >> a Linux kernel view point. >=20 > For arm64, so far we've not even been considering DT-based hotplug - as > far as I'm aware there would still be a big open question there around > notification mechanisms and how to describe them. The DT stuff so far > has come from the PowerPC folks, so it's probably worth seeing what > their ideas are. >=20 > ACPI-wise I've always assumed/hoped that hotplug-related things should > be sufficiently well-specified in UEFI that "do whatever x86/IA-64 do" > would be enough for us. As far as I can see in UEFI v2.8 -- and I had checked the spec before dumping the table with the many question marks on Shameer --, all the hot-plug language in the spec refers to USB and PCI hot-plug in the preboot environment. There is not a single word about hot-plug at OS runtime (regarding any device or component type), nor about memory hot-plug (at any time). Looking to x86 appears valid -- so what does the Linux kernel expect on that architecture, in the "ACPI" rows of the table? Shameer: if you (Huawei) are represented on the USWG / ASWG, I suggest re-raising the question on those lists too; at least the "ACPI" rows of the table. Thanks! Laszlo >=20 > Robin. >=20 >> (Hi Laszlo/Igor/Eric, please feel free to add/change if I have missed >> any valid >> points above). >> >> Thanks, >> Shameer >> [0] https://patchwork.kernel.org/cover/10890919/ >> [1] https://patchwork.kernel.org/patch/10863299/ >> [2] https://patchwork.kernel.org/patch/10890937/ >> >>