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 2ED55C04AB1 for ; Thu, 9 May 2019 21:49:27 +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 E3216217D7 for ; Thu, 9 May 2019 21:49:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E3216217D7 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]:33116 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOqus-0006f8-4o for qemu-devel@archiver.kernel.org; Thu, 09 May 2019 17:49:26 -0400 Received: from eggs.gnu.org ([209.51.188.92]:55535) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOqty-0006HO-E7 for qemu-devel@nongnu.org; Thu, 09 May 2019 17:48:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOqtw-0000P2-IR for qemu-devel@nongnu.org; Thu, 09 May 2019 17:48:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57100) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOqtr-0000L0-W6; Thu, 09 May 2019 17:48:24 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1E63A81112; Thu, 9 May 2019 21:48:22 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-120-234.rdu2.redhat.com [10.10.120.234]) by smtp.corp.redhat.com (Postfix) with ESMTP id 14BC65DF49; Thu, 9 May 2019 21:48:15 +0000 (UTC) To: Igor Mammedov References: <5FC3163CFD30C246ABAA99954A238FA83F1B6A66@lhreml524-mbs.china.huawei.com> <190831a5-297d-addb-ea56-645afb169efb@redhat.com> <20190509183520.6dc47f2e@Igors-MacBook-Pro> From: Laszlo Ersek Message-ID: Date: Thu, 9 May 2019 23:48:13 +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: <20190509183520.6dc47f2e@Igors-MacBook-Pro> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 09 May 2019 21:48:22 +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" , "xuwei \(O\)" , Anshuman Khandual , Catalin Marinas , "ard.biesheuvel@linaro.org" , "will.deacon@arm.com" , "qemu-devel@nongnu.org" , Shameerali Kolothum Thodi , Linuxarm , linux-mm , "qemu-arm@nongnu.org" , "eric.auger@redhat.com" , Jonathan Cameron , Robin Murphy , "linux-arm-kernel@lists.infradead.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 05/09/19 18:35, Igor Mammedov wrote: > On Wed, 8 May 2019 22:26:12 +0200 > Laszlo Ersek wrote: >=20 >> On 05/08/19 14:50, Robin Murphy wrote: >>> Hi Shameer, >>> >>> 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= boot >>>> even if we are booting with ACPI. Because of this, hotpluggable memo= ry >>>> may end up in zone normal and make it non-hot-un-pluggable even if G= uest >>>> 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 t= o >>>> 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 firmw= are can >>>> only >>>> =C2=A0 skip both hotpluggable cases. That's fine in that the firmwar= e will >>>> hog neither >>>> =C2=A0 type -- but is that OK for the OS as well, for both ACPI boot= and DT >>>> boot? >>>> >>>> Consider in particular the "hotpluggable & present, ACPI boot" case. >>>> Assuming >>>> we modify the firmware to skip "hotpluggable" altogether, the UEFI m= emmap >>>> 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() shou= ld 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 expecte= d >>>> here from >>>> a Linux kernel view point. >>> >>> 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 aroun= d >>> 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. >>> >>> ACPI-wise I've always assumed/hoped that hotplug-related things shoul= d >>> 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 o= n >> that architecture, in the "ACPI" rows of the table? >=20 > I could only answer from QEMU x86 perspective. > QEMU for x86 guests currently doesn't add hot-pluggable RAM into E820 > because of different linux guests tend to cannibalize it, making it non > unpluggable. The last culprit I recall was KASLR. >=20 > So I'd refrain from reporting hotpluggable RAM in GetMemoryMap() if > it's possible (it's probably hack (spec deosn't say anything about it) > but it mostly works for Linux (plug/unplug) and Windows guest also > fine with plug part (no unplug there)). I can accept this as a perfectly valid design. Which would mean, QEMU sho= uld mark each hotpluggable RAM range in the DTB for the firmware with the= special new property, regardless of its initial ("cold") plugged-ness, a= nd then the firmware will not expose the range in the GCD memory space ma= p, and consequently in the UEFI memmap either. IOW, our table is, thus far: OS boot (DT/ACPI) hotpluggable & ... GetMemoryMap() should report as D= T/ACPI should report as ----------------- ------------------ ------------------------------- -= ----------------------- DT present ABSENT ? DT absent ABSENT ? ACPI present ABSENT P= RESENT ACPI absent ABSENT A= BSENT In the firmware, I only need to care about the GetMemoryMap() column, so = I can work with this. Can someone please file a feature request at , for the ArmVirtPkg Package, with these detai= s? Thanks Laszlo >=20 > As for physical systems, there are out there ones that do report > hotpluggable RAM in GetMemoryMap(). >=20 >> 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 o= f >> the table. >> >> Thanks! >> Laszlo >> >>> >>> Robin. >>> >>>> (Hi Laszlo/Igor/Eric, please feel free to add/change if I have misse= d >>>> 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/ >>>> >>>> >> >=20