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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 42D92C43441 for ; Mon, 26 Nov 2018 17:11:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 11F5120663 for ; Mon, 26 Nov 2018 17:11:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 11F5120663 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=citrix.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727275AbeK0EGW (ORCPT ); Mon, 26 Nov 2018 23:06:22 -0500 Received: from smtp03.citrix.com ([162.221.156.55]:5522 "EHLO SMTP03.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726954AbeK0EGW (ORCPT ); Mon, 26 Nov 2018 23:06:22 -0500 X-IronPort-AV: E=Sophos;i="5.56,283,1539648000"; d="scan'208";a="71504935" Subject: Re: [Xen-devel] [PATCH v3] xen/balloon: Mark unallocated host memory as UNUSABLE To: Boris Ostrovsky , , CC: , , , References: <1513778746-6155-1-git-send-email-boris.ostrovsky@oracle.com> <7c833e3a-4a0b-e80c-91e2-4348d6959651@citrix.com> From: Igor Druzhinin Message-ID: Date: Mon, 26 Nov 2018 17:10:16 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: 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 26/11/2018 16:25, Boris Ostrovsky wrote: > On 11/25/18 8:00 PM, Igor Druzhinin wrote: >> On 20/12/2017 14:05, Boris Ostrovsky wrote: >>> Commit f5775e0b6116 ("x86/xen: discard RAM regions above the maximum >>> reservation") left host memory not assigned to dom0 as available for >>> memory hotplug. >>> >>> Unfortunately this also meant that those regions could be used by >>> others. Specifically, commit fa564ad96366 ("x86/PCI: Enable a 64bit BAR >>> on AMD Family 15h (Models 00-1f, 30-3f, 60-7f)") may try to map those >>> addresses as MMIO. >>> >>> To prevent this mark unallocated host memory as E820_TYPE_UNUSABLE (thus >>> effectively reverting f5775e0b6116) and keep track of that region as >>> a hostmem resource that can be used for the hotplug. >>> >>> Signed-off-by: Boris Ostrovsky >> This commit breaks Xen balloon memory hotplug for us in Dom0 with >> "hoplug_unpopulated" set to 1. The issue is that the common kernel >> memory onlining procedures require "System RAM" resource to be 1-st >> level. That means by inserting it under "Unusable memory" as the commit >> above does (intentionally or not) we make it 2-nd level and break memory >> onlining. > > What do you mean by 1st and 2nd level? > I mean the level of a resource in IOMEM tree (the one that's printed from /proc/iomem). 1-st level means its parent is root and so on. >> >> There are multiple ways to fix it depending on what was the intention of >> original commit and what exactly it tried to workaround. It seems it >> does several things at once: >> 1) Marks non-Dom0 host memory "Unusable memory" in resource tree. >> 2) Keeps track of all the areas safe for hotplug in Dom0 >> 3) Changes allocation algorithms itself in balloon driver to use those areas > > Pretty much. (3) is true in the sense that memory is first allocated > from hostmem_resource (which is non-dom0 RAM). > >> >> Are all the things above necessary to cover the issue in fa564ad96366 >> ("x86/PCI: Enable a 64bit BAR on AMD Family 15h (Models 00-1f, 30-3f, >> 60-7f)")? > > Not anymore, as far as that particular commit is concerned, but that's > because of 03a551734 ("x86/PCI: Move and shrink AMD 64-bit window to > avoid conflict") which was introduced after balloon patch. IIRC there > were some issues with fa564ad96366 unrelated to balloon. > If it's not a problem anymore IIUC, can we revert the change as it still breaks "hotplug_unpopulated=1" for the reasons I described above? > >> >> Can we remove "Unusable memory" resources as soon as we finished >> booting? Is removing on-demand is preferable over "shoot them all" in >> that case? > > The concern is that in principle nothing prevents someone else to do > exact same thing fa564ad96366 did, which is grab something from right > above end of RAM as the kernel sees it. And that can be done at any point. > Nothing prevents - true, but that's plainly wrong from OS point of view to grab physical ranges for something without knowing what's actually behind on that platform. I think we shouldn't consider this as a valid thing to do and don't try to workaround initially incorrect code. > > -boris > >> >> Does it even make sense to remove the 1-st level only restriction in >> kernel/resource.c ? > > >