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=-0.7 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 33AB4C47258 for ; Fri, 1 May 2020 16:57:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D5872173E for ; Fri, 1 May 2020 16:57:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="mG1IcDPB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729468AbgEAQ5K (ORCPT ); Fri, 1 May 2020 12:57:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1729278AbgEAQ5J (ORCPT ); Fri, 1 May 2020 12:57:09 -0400 Received: from mail-ed1-x544.google.com (mail-ed1-x544.google.com [IPv6:2a00:1450:4864:20::544]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12D09C08E859 for ; Fri, 1 May 2020 09:57:09 -0700 (PDT) Received: by mail-ed1-x544.google.com with SMTP id r16so7727186edw.5 for ; Fri, 01 May 2020 09:57:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=b9REn6X5SevH+LhOI4dPec9Nj6TaOfQYrUIVwbI6BoM=; b=mG1IcDPBM3HrlLCRXRv7RTTYgDzrduMX/5i/AlHCRx1Od+IpfQAyd0PeN//EsT0f5h 4ISFK8ebgantTgILgro22Ez5VhTT+nYI/BrtdR2EEj+8gVO8TXYZXeoKV+n5R7g8buaW 2yUZz1nPzY+7zON3G0XQLly2Qxcbo0G4O5Y6WDLkdJ7/fnZJpvu7siFKyoRkKMeO0fUZ /D0cspPD70+dXDGbdUVG4+VwKt7dWiqpPW5XzMx4fPRxJpNAeD6LnRMMzp+TiNYAZ53P qpaqeGLDtip2gO0UP/p8HNcC5mdTxBx8phoHoUjMgHPlB7ivmPuMEBOrgC5YppxB1E9h UOtg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=b9REn6X5SevH+LhOI4dPec9Nj6TaOfQYrUIVwbI6BoM=; b=qmV8rQUHHaKeUqpPdhwaMgKdUJKSy06u/xko3QUhyvbVK+m3TFrjnp4z/9t5ofhjkp hxP1pyHtif3S7fFYxHTVNWtJIfr74vt+qRPtIePXGVqgovF117CBxhPP5DipmXJjpnNh sW5FYV7BQyk7JKRwNizOL82CO1+nQRqWuv4bPrDzL9TVHKDug6sDrgrY5ZGqbj3IGNNM Qr8lfrGOEWUE46YScm/KtX89aS/3q+mW/D1KFbkOZvgrn7Fx3bD4Y/G/MisccyAIvvxu 59W+PhvT9Qll8Ve8tyaYK6z/g3Hgg7UVXEsfXn+Q3Ges/e4GMyZu6bpad6jZwJ4MQPoS SI9g== X-Gm-Message-State: AGi0PuYZ0/3a0Cpc/xPCajjkej7R9Bg7618587s1K4jOykO4uPm8w6PU pDdOg3cBQA1H8fHoVYlV3XOSGmb8Sv0oJ96h9OLm1w== X-Google-Smtp-Source: APiQypJO8dBUZTWLLj3LS+obr3vgzbWXqFSCM7dxYsl5W+J7URhuw83eMvKFki8Cpffi0gsBU7jQUIflqfdneq89wWQ= X-Received: by 2002:aa7:c643:: with SMTP id z3mr4236295edr.154.1588352227631; Fri, 01 May 2020 09:57:07 -0700 (PDT) MIME-Version: 1.0 References: <20200430102908.10107-1-david@redhat.com> <20200430102908.10107-3-david@redhat.com> <87pnbp2dcz.fsf@x220.int.ebiederm.org> <1b49c3be-6e2f-57cb-96f7-f66a8f8a9380@redhat.com> <871ro52ary.fsf@x220.int.ebiederm.org> <373a6898-4020-4af1-5b3d-f827d705dd77@redhat.com> <875zdg26hp.fsf@x220.int.ebiederm.org> <20200430152403.e0d6da5eb1cad06411ac6d46@linux-foundation.org> <5c908ec3-9495-531e-9291-cbab24f292d6@redhat.com> In-Reply-To: <5c908ec3-9495-531e-9291-cbab24f292d6@redhat.com> From: Dan Williams Date: Fri, 1 May 2020 09:56:56 -0700 Message-ID: Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: Introduce MHP_NO_FIRMWARE_MEMMAP To: David Hildenbrand Cc: Andrew Morton , "Eric W. Biederman" , Linux Kernel Mailing List , Linux MM , virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org, linuxppc-dev , Linux ACPI , linux-nvdimm , linux-hyperv@vger.kernel.org, linux-s390 , xen-devel , Michal Hocko , "Michael S . Tsirkin" , Michal Hocko , Pankaj Gupta , Wei Yang , Baoquan He Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 1, 2020 at 2:34 AM David Hildenbrand wrote: > > On 01.05.20 00:24, Andrew Morton wrote: > > On Thu, 30 Apr 2020 20:43:39 +0200 David Hildenbrand wrote: > > > >>> > >>> Why does the firmware map support hotplug entries? > >> > >> I assume: > >> > >> The firmware memmap was added primarily for x86-64 kexec (and still, is > >> mostly used on x86-64 only IIRC). There, we had ACPI hotplug. When DIMMs > >> get hotplugged on real HW, they get added to e820. Same applies to > >> memory added via HyperV balloon (unless memory is unplugged via > >> ballooning and you reboot ... the the e820 is changed as well). I assume > >> we wanted to be able to reflect that, to make kexec look like a real reboot. > >> > >> This worked for a while. Then came dax/kmem. Now comes virtio-mem. > >> > >> > >> But I assume only Andrew can enlighten us. > >> > >> @Andrew, any guidance here? Should we really add all memory to the > >> firmware memmap, even if this contradicts with the existing > >> documentation? (especially, if the actual firmware memmap will *not* > >> contain that memory after a reboot) > > > > For some reason that patch is misattributed - it was authored by > > Shaohui Zheng , who hasn't been heard from in > > a decade. I looked through the email discussion from that time and I'm > > not seeing anything useful. But I wasn't able to locate Dave Hansen's > > review comments. > > Okay, thanks for checking. I think the documentation from 2008 is pretty > clear what has to be done here. I will add some of these details to the > patch description. > > Also, now that I know that esp. kexec-tools already don't consider > dax/kmem memory properly (memory will not get dumped via kdump) and > won't really suffer from a name change in /proc/iomem, I will go back to > the MHP_DRIVER_MANAGED approach and > 1. Don't create firmware memmap entries > 2. Name the resource "System RAM (driver managed)" > 3. Flag the resource via something like IORESOURCE_MEM_DRIVER_MANAGED. > > This way, kernel users and user space can figure out that this memory > has different semantics and handle it accordingly - I think that was > what Eric was asking for. > > Of course, open for suggestions. I'm still more of a fan of this being communicated by "System RAM" being parented especially because that tells you something about how the memory is driver-managed and which mechanism might be in play. What about adding an optional /sys/firmware/memmap/X/parent attribute. This lets tooling check if it cares via that interface and lets it lookup the related infrastructure to interact with if it would do something different for virtio-mem vs dax/kmem?