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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 019BFC433FF for ; Mon, 29 Jul 2019 14:53:51 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C780D2054F for ; Mon, 29 Jul 2019 14:53:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C780D2054F 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 ([::1]:52814 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hs726-0001g6-5K for qemu-devel@archiver.kernel.org; Mon, 29 Jul 2019 10:53:50 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36379) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hs70v-0007ys-7x for qemu-devel@nongnu.org; Mon, 29 Jul 2019 10:52:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hs70u-0000SA-4K for qemu-devel@nongnu.org; Mon, 29 Jul 2019 10:52:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60014) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hs70t-0000Ro-Vv; Mon, 29 Jul 2019 10:52:36 -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 40B803082E90; Mon, 29 Jul 2019 14:52:35 +0000 (UTC) Received: from dell-r430-03.lab.eng.brq.redhat.com (dell-r430-03.lab.eng.brq.redhat.com [10.37.153.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id 485245D9E2; Mon, 29 Jul 2019 14:52:34 +0000 (UTC) From: Igor Mammedov To: qemu-devel@nongnu.org Date: Mon, 29 Jul 2019 10:52:27 -0400 Message-Id: <20190729145229.4333-1-imammedo@redhat.com> 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 [10.5.110.46]); Mon, 29 Jul 2019 14:52:35 +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: [Qemu-devel] [PATCH RFC 0/2] s390: stop abusing memory_region_allocate_system_memory() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pbonzini@redhat.com, qemu-s390x@nongnu.org, dgilbert@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" While looking into unifying guest RAM allocation to use hostmem backends for initial RAM (especially when -mempath is used) and retiring memory_region_allocate_system_memory() API, leaving only single hostmem backend, I was inspecting how currently it is used by boards and it turns out several boards abuse it by calling the function several times (despite documented contract forbiding it). s390 is one of such boards where KVM limitation on memslot size got propagated to board design and memory_region_allocate_system_memory() was abused to satisfy KVM requirement for max RAM chunk where memory region alias would suffice. Unfortunately, memory_region_allocate_system_memory() usage created migration dependency where guest RAM is transferred in migration stream as several RAMBlocks if it's more than KVM_SLOT_MAX_BYTES. In order to replace these several RAM chunks with a single memdev and keep it working with KVM memslot size limit and migration compatible, following was done: * [2/2] use memory region aliases to partition hostmem backend RAM on KVM_SLOT_MAX_BYTES chunks, which should keep KVM side working * [1/2] hacked memory region aliases (to ram memory regions only) to have its own RAMBlocks pointing to RAM chunks owned by aliased memory region. While it's admittedly a hack, but it's relatively simple and allows board code rashape migration stream as necessary I haven't tried to use migratable aliases on x86 machines, but with it it could be possible to drop legacy RAM allocation and compat knob (cd5ff8333a) dropping '-numa node,mem' completely even for old machines. PS: Tested with ping pong cross version migration on s390 machine (with reduced KVM_SLOT_MAX_BYTES since I don't have access to large enough host) Igor Mammedov (2): memory: make MemoryRegion alias migratable s390: do not call memory_region_allocate_system_memory() multiple times exec.c | 7 ++++--- hw/s390x/s390-virtio-ccw.c | 20 +++++++++++++++----- memory.c | 5 +++++ 3 files changed, 24 insertions(+), 8 deletions(-) -- 2.18.1