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=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 133A1C04A6B for ; Wed, 8 May 2019 20:09:33 +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 D122520989 for ; Wed, 8 May 2019 20:09:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D122520989 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]:43242 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOSsd-0007Pv-UD for qemu-devel@archiver.kernel.org; Wed, 08 May 2019 16:09:31 -0400 Received: from eggs.gnu.org ([209.51.188.92]:45123) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOSrn-00074g-CE for qemu-devel@nongnu.org; Wed, 08 May 2019 16:08:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOSrl-0001NI-UC for qemu-devel@nongnu.org; Wed, 08 May 2019 16:08:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51024) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOSrj-0001Ke-2F; Wed, 08 May 2019 16:08:35 -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 53AA789C40; Wed, 8 May 2019 20:08:33 +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 D04335D9D1; Wed, 8 May 2019 20:08:24 +0000 (UTC) To: Shameerali Kolothum Thodi , "robin.murphy@arm.com" , "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: Date: Wed, 8 May 2019 22:08:23 +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: <5FC3163CFD30C246ABAA99954A238FA83F1B6A66@lhreml524-mbs.china.huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 [10.5.110.27]); Wed, 08 May 2019 20:08:33 +0000 (UTC) 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 12:15, 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 memory > may end up in zone normal and make it non-hot-un-pluggable even if Guest > 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 > hotpluggable & present, from hotpluggable & absent. The firmware can only > skip both hotpluggable cases. That's fine in that the firmware will hog neither > 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 memmap > 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) hotpluggable & ... GetMemoryMap() should report as DT/ACPI should report as > ----------------- ------------------ ------------------------------- ------------------------ > DT present ? ? > DT absent ? ? > ACPI present ? ? > ACPI absent ? ? > > 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. > > (Hi Laszlo/Igor/Eric, please feel free to add/change if I have missed any valid > points above). I'm happy with your summary, thank you! Laszlo > > Thanks, > Shameer > [0] https://patchwork.kernel.org/cover/10890919/ > [1] https://patchwork.kernel.org/patch/10863299/ > [2] https://patchwork.kernel.org/patch/10890937/ > >