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,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 C4D7EC433FF for ; Mon, 5 Aug 2019 08:55:17 +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 9B2EC20B1F for ; Mon, 5 Aug 2019 08:55:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9B2EC20B1F 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]:51786 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1huYlw-0002GA-TK for qemu-devel@archiver.kernel.org; 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charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Mon, 05 Aug 2019 08:54:45 +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] [PATCH for-4.2 v3 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: thuth@redhat.com, david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, qemu-s390x@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 2 Aug 2019 17:04:21 +0200 Christian Borntraeger wrote: > On 02.08.19 16:59, Christian Borntraeger wrote: > > > > > > On 02.08.19 16:42, Christian Borntraeger wrote: > >> On 02.08.19 15:32, Igor Mammedov wrote: > >>> Changelog: > >>> since v2: > >>> - break migration from old QEMU (since 2.12-4.1) for guest with >8TB RAM > >>> and drop migratable aliases patch as was agreed during v2 review > >>> - drop 4.2 machines patch as it's not prerequisite anymore > >>> since v1: > >>> - include 4.2 machines patch for adding compat RAM layout on top > >>> - 2/4 add missing in v1 patch for splitting too big MemorySection on > >>> several memslots > >>> - 3/4 amend code path on alias destruction to ensure that RAMBlock is > >>> cleaned properly > >>> - 4/4 add compat machine code to keep old layout (migration-wise) for > >>> 4.1 and older machines > >>> > >>> > >>> 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. During v2 review it was agreed to ignore > >>> migration breakage (documenting it in release notes) and leaving only KVM fix. > >>> > >>> In order to replace these several RAM chunks with a single memdev and keep it > >>> working with KVM memslot size limit, following was done: > >>> * [1/2] split too big RAM chunk inside of KVM code on several memory slots > >>> if necessary > >>> * [2/2] drop manual ram splitting in s390 code > >>> > >>> > >>> CC: pbonzini@redhat.com > >>> CC: qemu-s390x@nongnu.org > >>> CC: borntraeger@de.ibm.com > >>> CC: thuth@redhat.com > >>> CC: david@redhat.com > >>> CC: cohuck@redhat.com > >> > >> With the fixup this patch set seems to work on s390. I can start 9TB guests and > >> I can migrate smaller guests between 4.1+patch and 4.0 and 3.1. I currently can > >> not test migration for the 9TB guest due to lack of a 2nd system. > > > > I have to correct myself. The 9TB guest started up but it does not seem to do > > anything useful (it hangs). > > Seems that the userspace addr is wrong (its the same). > [pid 258234] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=0, flags=0, guest_phys_addr=0, memory_size=8796091973632, userspace_addr=0x3fff7d00000}) = 0 > [pid 258234] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=1, flags=0, guest_phys_addr=0x7fffff00000, memory_size=1099512676352, userspace_addr=0x3fff7d00000}) = 0 It's a bug in 1/2, I forgot to advance mem->ram along with mem->start_addr. Let me fix it and simulate it on small s390 host (/me sorry for messy patches) it won't test migration properly but should be sufficient for testing KVM code patch.