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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 30 Sep 2019 12:00:30 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x8UB0TJw34668698 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 30 Sep 2019 11:00:30 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C7AE8A405B; Mon, 30 Sep 2019 11:00:29 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 80DB0A406E; Mon, 30 Sep 2019 11:00:29 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.146]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 30 Sep 2019 11:00:29 +0000 (GMT) Subject: Re: [PATCH v7 0/4] s390: stop abusing memory_region_allocate_system_memory() To: Igor Mammedov , qemu-devel@nongnu.org References: <20190924144751.24149-1-imammedo@redhat.com> From: Christian Borntraeger Openpgp: preference=signencrypt Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190924144751.24149-1-imammedo@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19093011-0028-0000-0000-000003A3F136 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19093011-0029-0000-0000-0000246619DA Message-Id: <00cbdb6b-10a9-145a-2788-82b412add171@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-09-30_07:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1909300117 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 148.163.156.1 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, peterx@redhat.com, qemu-s390x@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 24.09.19 16:47, Igor Mammedov wrote: > Changelog: > since v6: > - include and rebase on top of > [PATCH 0/2] kvm: clear dirty bitmaps from all overlapping memslots > https://www.mail-archive.com/qemu-devel@nongnu.org/msg646200.html > - minor fixups suggested during v6 review > - more testing incl. hacked x86 > since v5: > - [1/2] fix migration that wasn't starting and make sure that KVM part > is able to handle 1:n MemorySection:memslot arrangement > since v3: > - fix compilation issue > - advance HVA along with GPA in kvm_set_phys_mem() > 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, the later was modified to deal with > memory section split on several KVMSlots and manual RAM splitting in s390 > was replace by single memory_region_allocate_system_memory() call. > > Tested: > * s390 with hacked KVM_SLOT_MAX_BYTES = 128Mb > - guest reboot cycle in ping-pong migration > * x86 with hacke max memslot = 128 and manual_dirty_log_protect enabled > - ping-pong migration with workload dirtying RAM around a split area > Thanks, v7 applied to s390-next.