From patchwork Fri Oct 12 23:48:27 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jag Raman X-Patchwork-Id: 10639387 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id BC34814BD for ; Fri, 12 Oct 2018 23:53:43 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A4D2322362 for ; Fri, 12 Oct 2018 23:53:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 97B232B9AF; Fri, 12 Oct 2018 23:53:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.7 required=2.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,UNPARSEABLE_RELAY autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 9EA0B22362 for ; Fri, 12 Oct 2018 23:53:40 +0000 (UTC) Received: from localhost ([::1]:43099 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gB7FT-0003JU-VR for patchwork-qemu-devel@patchwork.kernel.org; Fri, 12 Oct 2018 19:53:39 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60826) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gB7Ax-0008C1-Op for qemu-devel@nongnu.org; Fri, 12 Oct 2018 19:49:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gB7Aq-0006Uj-99 for qemu-devel@nongnu.org; Fri, 12 Oct 2018 19:48:57 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:47340) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gB7Ao-0006RA-2Y for qemu-devel@nongnu.org; Fri, 12 Oct 2018 19:48:52 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w9CNiJ2W088173 for ; Fri, 12 Oct 2018 23:48:46 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id; s=corp-2018-07-02; bh=P9gmmJwU2yriFhVO32KXyAChLSyQ9afncHlozc9l7qA=; b=H0AzjUApvn8PVmbPvruIArQADIhCa6OZE5OM6uSITePKCd9ko0TfxRCxCsXsBrkXaPVr 6Lqn729jlqd/l1cYs35HcAnCpg8Ob19+uiiNfVkReayiG3sEEQPYMo4KxrmLff5udc2s +kXnzp7ebN9ZOxdsYciyiR0rFIERQG8Gyfgf9/0jjpoqjgEICgrBwcSLlT/0wS9qifIe cAh4TFR487V2zsQn4kOAPQtyRnwKPo4mpQ0Oi2hAQaMGU65od2oHTzG18saQGGOfdmRb qekSAMJdKCsvIPE4kYACbiiijtmu4gq78sZLiK37BxKArdDu7L3hfYBfzYKVEPnYM8GU Zw== Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234]) by userp2120.oracle.com with ESMTP id 2mxnprndsm-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Fri, 12 Oct 2018 23:48:45 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id w9CNmiDa009541 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Fri, 12 Oct 2018 23:48:44 GMT Received: from abhmp0018.oracle.com (abhmp0018.oracle.com [141.146.116.24]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w9CNmixV008247 for ; Fri, 12 Oct 2018 23:48:44 GMT Received: from jaraman-bur-1.us.oracle.com (/10.152.33.39) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 12 Oct 2018 23:48:44 +0000 From: Jagannathan Raman To: qemu-devel@nongnu.org Date: Fri, 12 Oct 2018 19:48:27 -0400 Message-Id: X-Mailer: git-send-email 1.8.3.1 X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9044 signatures=668706 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1810120235 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] X-Received-From: 156.151.31.85 Subject: [Qemu-devel] [RFC PATCH v1 0/8] multi-process QEMU X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: elena.ufimtseva@oracle.com, john.g.johnson@oracle.com, jag.raman@oracle.com, Kanth.Ghatraju@oracle.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP Hi The multi-process QEMU project proposal written by John Johnson is copied below. This patchset implements part of the proposal. The goal is to run emulated devices as standalone processes. To begin with, we've chosen to run lsi53c895a as a standalone process /remote device, based on the architecture described in the proposal. This patchset implements some of the fundamental parts necessary to implement the remote device. The remote device sets up a PCI host bridge. Future patches would add leaf devices to the PCI host. A "proxy device" is implemented, which acts as proxy for the remote device. It provides the remote device with access to the RAM, which is needed to perform DMA. It also handles PCI BAR & config space accesses. Thanks! From: John G Johnson Date: Mon, 24 Sep 2018 13:23:03 -0700 Subject: multi-process QEMU Greetings, At last year's KVM forum, Konrad Wilk and Marc-Andre Lureau presented on multi-prcess QEMU: https://www.linux-kvm.org/images/f/fc/KVM_FORUM_multi-process.pdf At Oracle, we've started a project to implement this concept. When we shared the proposal with Marc-Andre, he suggested we also share it with you. The current proposal is attached. We are working on coding, and expect to have an initial set of patches in a couple weeks. These patches will just cover setting up the same PCI tree in both processes. Jag Raman will attend this year's KVM forum, and will propose a BoF session on the subject. By this time we will have send out another set of patches that cover separating a PCI leaf device. We'd appreciate any comments you have, both in the proposal itself, and on the above plan. Many thanks for your time on this. JJ Disaggregating QEMU QEMU is often used as the hypervisor for virtual machines running in the Oracle cloud. Since one of the advantages of cloud computing is the ability to run many VMs from different tenants in the same cloud infrastructure, a guest that compromised its hypervisor could potentially use the hypervisor's access privileges to access data it is not authorized for. QEMU can be susceptible to security attack because it is a large, monolithic program that provides many features to the VMs it services. Many of these feature can be configured out of QEMU, but even a reduced configuration QEMU has a large amount of code a guest can potentially attack in order to gain additional privileges. 1. QEMU services QEMU can be broadly described as providing three main services. One is a VM control point, where VMs can be created, migrated, re-configured, and destroyed. A second is to emulate the CPU instructions within the VM, often accelerated by HW virtualization features such as Intel's VT extensions. Finally, it provides IO services to the VM by emulating HW IO devices, such as disk and network devices. 1.1 A disaggregated QEMU A disaggregated QEMU involves separating QEMU services into separate host processes. Each of these processes can be given only the privileges it needs to provide its service, e.g., a disk service could be given access only the the disk images it provides, and not be allowed to access other files, or any network devices. An attacker who compromised this service would not be able to use this exploit to access files or devices beyond what the disk service was given access to. A control QEMU process would remain, but in disaggregated mode, it would be a control point that exec()s the processes needed to support the VM being created, but have no direct interface to the VM. During VM execution, it would still provide the user interface to hot-plug devices or live migrate the VM. A first step in creating a disaggregated QEMU is to separate IO services from the main QEMU program, which would continue to provide CPU emulation. i.e., the control process would also be the CPU emulation process. In a later phase, CPU emulation could be separated from the QEMU control process. 2. Disaggregating IO services Disaggregating IO services is a good place to begin QEMU disaggregating for a couple of reasons. One is the sheer number of IO devices QEMU can emulate provides a large surface of interfaces which could potentially be exploited, and, indeed, have been a source of exploits in the past. Another is the modular nature of QEMU device emulation code provides interface points where the QEMU functions that perform device emulation can be separated from the QEMU functions that manage the emulation of guest CPU instructions. 2.1 QEMU device emulation QEMU uses a object oriented SW architecture for device emulation code. Configured objects are all compiled into the QEMU binary, then objects are instantiated by name when used by the guest VM. For example, the code to emulate a device named "foo" is always present in QEMU, but its instantiation code is only run when a device named "foo" is included in the target VM (such as via the QEMU command line as -device "foo".) The object model is hierarchical, so device emulation code can name its parent object (such as "pci-device" for a PCI device) and QEMU will instantiate a parent object before calling the device's instantiation code. 2.2 Current separation models In order to separate the device emulation code from the CPU emulation code, the device object code must run in a different process. There are a couple of existing QEMU features that can run emulation code separately from the main QEMU process. These are examined below. 2.2.1 vhost user model Virtio guest device drivers can be connected to vhost user applications in order to perform their IO operations. This model uses special virtio device drivers in the guest and vhost user device objects in QEMU, but once the QEMU vhost user code has configured the vhost user application, mission-mode IO is performed by the application. The vhost user application is a daemon process that can be contacted via a known UNIX domain socket. 2.2.1.1 vhost socket As mentioned above, one of the tasks of the vhost device object within QEMU is to contact the vhost application and send it configuration information about this device instance. As part of the configuration process, the application can also be sent other file descriptors over the socket, which then can be used by the vhost user application in various ways, some of which are described below. 2.2.1.2 vhost MMIO store acceleration VMs are often run using HW virtualization features via the KVM kernel driver. This driver allows QEMU to accelerate the emulation of guest CPU instructions by running the guest in a virtual HW mode. When the guest executes instructions that cannot be executed by virtual HW mode, execution return to the KVM driver so it can inform QEMU to emulate the instructions in SW. One of the events that can cause a return to QEMU is when a guest device driver accesses an IO location. QEMU then dispatches the memory operation to the corresponding QEMU device object. In the case of a vhost user device, the memory operation would need to be sent over a socket to the vhost application. This path is accelerated by the QEMU virtio code by setting up an eventfd file descriptor that the vhost application can directly receive MMIO store notifications from the KVM driver, instead of needing them to be sent to the QEMU process first. 2.2.1.3 vhost interrupt acceleration Another optimization used by the vhost application is the ability to directly inject interrupts into the VM via the KVM driver, again, bypassing the need to send the interrupt back to the QEMU process first. The QEMU virtio setup code configures the KVM driver with an eventfd that triggers the device interrupt in the guest when the eventfd is written. This irqfd file descriptor is then passed to the vhost user application program. 2.2.1.4 vhost access to guest memory The vhost application is also allowed to directly access guest memory, instead of needing to send the data as messages to QEMU. This is also done with file descriptors sent to the vhost user application by QEMU. These descriptors can be mmap()d by the vhost application to map the guest address space into the vhost application. IOMMUs introduce another level of complexity, since the address given to the guest virtio device to DMA to or from is not a guest physical address. This case is handled by having vhost code within QEMU register as a listener for IOMMU mapping changes. The vhost application maintains a cache of IOMMMU translations: sending translation requests back to QEMU on cache misses, and in turn receiving flush requests from QEMU when mappings are purged. 2.2.1.5 applicability to device separation Much of the vhost model can be re-used by separated device emulation. In particular, the ideas of using a socket between QEMU and the device emulation application, using a file descriptor to inject interrupts into the VM via KVM, and allowing the application to mmap() the guest should be re-used. There are, however, some notable differences between how a vhost application works and the needs of separated device emulation. The most basic is that vhost uses custom virtio device drivers which always trigger IO with MMIO stores. A separated device emulation model must work with existing IO device models and guest device drivers. MMIO loads break vhost store acceleration since they are synchronous - guest progress cannot continue until the load has been emulated. By contrast, stores are asynchronous, the guest can continue after the store event has been sent to the vhost application. Another difference is that in the vhost user model, a single daemon can support multiple QEMU instances. This is contrary to the security regime desired, in which the emulation application should only be allowed to access the files or devices the VM it's running on behalf of can access. 2.2.2 qemu-io model Qemu-io is a test harness used to test changes to the QEMU block backend object code. (e.g., the code that implements disk images for disk driver emulation) Qemu-io is not a device emulation application per se, but it does compile the QEMU block objects into a separate binary from the main QEMU one. This could be useful for disk device emulation, since its emulation applications will need to include the QEMU block objects. 2.3 New separation model based on proxy objects A different model based on proxy objects in the QEMU program communicating with proxy objects the separated emulation programs could provide separation while minimizing the changes needed to the device emulation code. The rest of this section is a discussion of how a proxy object model would work. 2.3.1 command line specification The QEMU command line options will need to be modified to indicate which items are emulated by a separate program, and which remain emulated by QEMU itself. 2.3.1.1 devices Devices that are to be emulated in a separate process will be identified by using "-rdevice" on the QEMU command line in lieu of "-device". The device's other options will also be included in the command line, with the addition of a "command" option that specifies the remote program to execute to emulate the device. e.g., an LSI SCSI controller and disk can be specified as: -device lsi53c895a,id=scsi0 device -device scsi-hd,drive=drive0,bus=scsi0.0,scsi-id=0 If these devices are emulated with program "lsi-scsi," the QEMU command line would be: -rdevice lsi53c895a,id=scsi0,command="lsi-scsi" -rdevice scsi-hd,drive=drive0,bus=scsi0.0,scsi-id=0 Some devices are implicitly created by the machine object. e.g., the "q35" machine object will create its PCI bus, and attach a "ich9-ahci" IDE controller to it. In this case, options will need to be added to the "-machine" command line. e.g., -machine pc-q35,ide-command="ahci-ide" will use the "ahci-ide" program to emulate the IDE controller and its disks. The disks themselves still need to be specified with "-rdevice", e.g., -rdevice ide-hd,drive=drive0,bus=ide.0,unit=0 The "-rdevice" devices will be parsed into a separate QemuOptsList from "-device" ones, but will still have "driver" as the implied name of the initial option. 2.3.1.2 backends The device's backend would similarly have a changed command line specification. e.g., a qcow2 block backend specified as: -blockdev driver=file,node-name=file0,filename=disk-file0 -blockdev driver=qcow2,node-name=drive0,file=file0 becomes -rblockdev driver=file,node-name=file0,filename=disk-file0 -rblockdev driver=qcow2,node-name=drive0,file=file0 As is the case with devices, "-rblockdev" backends will be parsed into their own BlockdevOptions_queue. 2.3.2 device proxy objects QEMU has an object model based on sub-classes inherited from the "object" super-class. The sub-classes that are of interest here are the "device" and "bus" sub-classes whose child sub-classes make up the device tree of a QEMU emulated system. The proxy object model will use device proxy objects to replace the device emulation code within the QEMU process. These objects will live in the same place in the object and bus hierarchies as the objects they replace. i.e., the proxy object for an LSI SCSI controller will be a sub-class of the "pci-device" class, and will have the same PCI bus parent and the same SCSI bus child objects as the LSI controller object it replaces. After the QEMU command line has been parsed, the "-rdevice" devices will be instantiated in the same manner as "-device" devices are. (i.e., qdev_device_add()). In order to distinguish them from regular "-device" device objects, their class name will be the name of the class it replaces, with "-proxy" appended. e.g., the "scsi-hd" proxy class will be "scsi-hd-proxy" 2.3.2.1 object initialization QEMU object initialization occurs in two phases. The first initialization happens once per object class. (i.e., there can be many SCSI disks in an emulated system, but the "scsi-hd" class has its class_init() function called only once) The second phase happens when each object's instance_init() function is called to initialize each instance of the object. All device objects are sub-classes of the "device" class, so they also have a realize() function that is called after instance_init() is called and after the object's static properties have been initialized. Many device objects don't even provide an instance_init() function, and do all their per-instance work in realize(). 2.3.2.1.1 class_init The class_init() method of a proxy object will, in general behave similarly to the object it replaces, including setting any static properties and methods needed by the proxy. 2.3.2.1.2 instance_init / realize The instance_init() and realize() functions would only need to perform tasks related to being a proxy, such are registering its own MMIO handlers, or creating a child bus that other proxy devices can be attached to later. They also need to add a "json_device" string property that contains the JSON representation of the command line options used to create the object. This JSON representation is used to create the corresponding object in an emulation process. e.g., for an LSI SCSI controller invoked as: -rdevice lsi53c895a,id=scsi0,command="lsi-scsi" the proxy object would create a { "driver" : "lsi53c895a", "id" : "scsi0" } JSON description. The "driver" option is assigned to the device name when the command line is parsed, so the "-proxy" appended by the command line parsing code must be removed. The "command" option isn't needed in the JSON description since it only applies to the proxy object in the QEMU process. Other tasks will are device-specific. PCI device objects will initialize the PCI config space in order to make a valid PCI device tree within the QEMU process. Disk devices will probe their backend object to get its JSON description, and publish this description as a "json_backend" string property (see the backend discussion below.) 2.3.2.2 address space registration Most devices are driven by guest device driver accesses to IO addresses or ports. The QEMU device emulation code uses QEMU's memory region function calls (such as memory_region_init_io()) to add callback functions that QEMU will invoke when the guest accesses the device's areas of the IO address space. When a guest driver does access the device, the VM will exit HW virtualization mode and return to QEMU, which will then lookup and execute the corresponding callback function. A proxy object would need to mirror the memory region calls the actual device emulator would perform in its initialization code, but with its own callbacks. When invoked by QEMU as a result of a guest IO operation, they will forward the operation to the device emulation process via a proxy_proc_send() call. Any response will be read via proxy_proc_recv(). Note that the callbacks are called with an address space lock, so it would not be a appropriate to synchronously wait for any response. Instead the QEMU code must be changed to check if the thread needs to sleep after the address_space_rw() call (in kvm_cpu_exec().) 2.3.2.3 PCI config space PCI devices also have a configuration space that can be accessed by the guest driver. Guest accesses to this space is not handled by the device emulation object, but by it's PCI parent object. Much of this space is read-only, but certain registers (especially BAR and MSI-related ones) need to be propagated to the emulation process. 2.3.2.3.1 PCI parent proxy One way to propagate guest PCI config accesses is to create a "pci-device-proxy" class that can serve as the parent of a PCI device proxy object. This class's parent would be "pci-device" and it would override the PCI parent's config_read and config_write methods with ones that forward these operations to the emulation program. 2.3.2.4 interrupt receipt A proxy for a device that generates interrupts will receive the interrupt indication via the read callback it provided to proxy_ctx_alloc(). The interrupt indication would then be sent up to its bus parent to be injected into the guest. For example, a PCI device object may use pci_set_irq(). 2.3.3 device backends Each type of device has backends which perform IO operations in the host system. For example, block backend objects emulate the disk images configured into the VM. While block backends are implemented as objects, not all backends are. For example, display backends (e.g., vnc) are not objects, they register a set of virtual functions that are called by QEMU's display emulation. These device backends also need run in the device emulation processes, and the emulation process must be given access the the corresponding host files or devices. 2.3.3.1 block backends Block backends are objects that can implement file protocols (such as a local file or an iSCSI volume), implement disk image formats (such as qcow2), or serve as a request filter (such as IO throttling). They are often stacked on each other (such as a qcow2 format on a local file protocol.) They're are named by "node-name" properties that are then matched to "drive" properties of the corresponding disk devices. Block backend objects are not part of the QEMU object model (i.e., they're not sub-classes of "object"). They are instantiated when the bdrv_file_open() method is invoked with a Qdict dictionary of the backend's command line options. 2.3.3.1.1 initialization When a "-rblockdev" backend is initialized, it will not open the underlying backend object, as is done for "-blockdev" backends. Instead, it will create a BlockDriverState node that has a proxy name and the original options Qdict. The proxy name will consist of the backend's node-name with "-peer" appended to it (i.e., a "drive0" node-name would have a "drive0-peer" peer.) A proxy backend object with then be opened, using an initialization Qdict containing the "node-name" of the underlying backend, so that disk device objects and QMP commands can find it. The proxy's Qdict will also be given the proxy name as a "peer" property so it can lookup its underlying backend object and its associated Qdict. 2.3.3.1.2 bdrv_probe_json This API returns the JSON description of the peer of a given backend proxy. It will be used by disk device proxy objects to get the JSON descriptions of the block backend (and any backends layered below) needed to emulate the disk image. 2.3.3.1.3 bdrv_get_json This is a new block backend object method that returns the JSON description this object, and all of its underlying objects. It will recursively descend any layered backend objects (e.g., a format object will call its underlying protocol object) This method can be invoked on an object that has not been opened. It will mainly be used by bdrv_probe_json(). 2.3.3.1.4 bdrv_assign_proxy_name The API creates the node with a proxy name, and enters it on a list of peer nodes. This list can be searched by proxy backends to find their associated peers. 2.3.3.1.5 QMP commands Various QMP command operate on blockdevs. These will need to work on rblockevs in separated processes as well. There are several cases that need to be handled. 2.3.3.1.5.1 adding rblockdevs QMP allows users to add blockdevs to a running QEMU instance. This is done not just to hot-plug a disk device into a guest, but also for advanced blockdev features such as changing quorum devices. Likewise, QMP needs be able to add an rblockdev to the guest, so similar operations can be performed on devices being emulated in a separate process. This operation doesn't need to be performed differently from adding an rblockdev from the command line. Blockdevs are added with a qmp_blockdev_add() routine that can be called from either the command line parser or from QMP. Note the name of the C routine called from QMP is generated by a python script, so a "rblockdev-add" command must be implemented by qmp_rblockdev_add(). 2.3.3.1.5.2 targeted commands Many QMP commands operate on specified blockdevs. These commands will find the proxy node when they lookup the targeted name, which will then forward the request to the emulation process managing the peer node. 2.3.3.1.5.3 blockdev lists Several QMP query commands (such as query-block or query-block-jobs) operate on all blockdevs. These will function much like targeted commands, with the proxy nodes forwarding the request to its peer emulation process. 2.3.4 proxy APIs There will be a set of APIs provided by a process execution service for proxy objects to use to manage the separate emulation program. 2.3.4.1 proxy_register A proxy device object must register itself with the proxy_register() API. The registration call will include validation and execution callbacks that will be invoked after the emulated machine has been setup in QEMU. 2.3.4.1.1 validation callback This callback will invoked after all devices in the emulated system have been initialized. Its purpose is to validate the device configuration by checking that its parent and child bus objects are compatible with being proxied. For example, a disk controller can check that all the devices on its bus are all proxy objects, or a disk object can check that its backend object is a proxy. If any of the validation callbacks return an error, QEMU will exit. If there are no errors, the execution callbacks will be invoked. 2.3.4.1.2 execution callback A device proxy object that manages an emulation process will provide an execution callback in its proxy_register() call. This callback will allocate an execution context with proxy_ctx_alloc(), marshal the arguments needed for the emulation program, and invoke proxy_execute() to execute it. 2.3.4.2 proxy_ctx_alloc Before the emulation program can be executed, the proxy object must call proxy_ctx_alloc() to create an execution context for the process. The execution context will serve as a handle on which the other proxy APIs operate. 2.3.4.3 proxy_ctx_callbacks This API registers two callback functions: get_reply() and get_request(), on the context. get_reply() is invoked to handle replies to requests sent to the emulation process. get_request() is invoked to handle requests from the emulation process. This API can be called multiple times on the same context; a class field within an incoming message indicates which callbacks will be invoked. 2.3.4.4 proxy_execute This function executes an emulation program. It needs to be provided with an execution context, the file to execute, and any arguments needed by the program. Before executing the given program, it will setup the communications channels for the new process. 2.3.5 communication with emulation process The execution service will setup two communication channels between the main QEMU process and the emulation process. The channels will be created using socketpair() so that file descriptors can be passed from QEMU to the process. 2.3.5.1 requests to emulation process The stdin file descriptor of the emulation process will be used for requests from QEMU to the emulation process. The execution service provides APIs to send and receive messages from the emulation process. 2.3.5.1.1 proxy_proc_send This API is for the proxy object in QEMU to send messages to the emulation process. Its arguments will include an execution context in addition to the actual message. 2.3.5.1.2 proxy_proc_recv This API receives replies from the emulation process. It requires the execution context of the target process, and will usually be called from the get_reply() callback specified in proxy_ctx_alloc. 2.3.5.2 requests to QEMU process The stdout file descriptor to the emulation process will be used for requests from the emulation process to QEMU. As with requests to the emulation process, APIs will be provided to facilitate communication. 2.3.5.2.1 proxy_qemu_recv This API receives requests from the emulation process. It requires the execution context of the target process, and will usually be called from the get_request() callback specified in proxy_ctx_alloc. 2.3.5.2.2 proxy_qemu_send This API is for the proxy object in QEMU to send replies to the emulation process. Its arguments will include an execution context in addition to the actual reply. 2.3.5.3 JSON descriptions The initial messages sent to the emulation process will describe the devices its will be tasked to emulate. The will be described as JSON arrays of backend and device objects that need to be instantiated by the emulation process. 2.3.5.3.1 backend JSON The device proxy object will aggregate the "json_backend" properties from the disk devices on the bus it controls, and send them as a JSON array of objects. e.g., this command line: -rblockdev driver=file,node-name=file0,filename=disk-file0 -rblockdev driver=qcow2,node-name=drive0,file=file0 would generate [ { "driver" : "file", "node-name" : "file0", "filename" : "disk-file0" }. { "driver" : "qcow2", "node-name" : "drive0", "file" : "file0" } ] 2.3.5.3.2 device JSON The device proxy object will aggregate a JSON description of itself and devices on the bus it controls (via their "json_device" properties), and send them to the emulation process as a JSON array of objects. 2.3.5.4 DMA operations DMA operations would be handled much like vhost applications do. One of the initial messages sent to the emulation process is a guest memory table. Each entry in this table consists of a file descriptor and size that the emulation process can mmap() to directly access guest memory, similar to vhost_user_set_mem_table(). Note guest memory must be backed by file descriptors, such as when QEMU is given the "-mem-path" command line option. 2.3.5.5 IOMMU operations When the emulated system includes an IOMMU, the proxy execution service will need to handle IOMMU requests from the emulation process using an address_space_get_iotlb_entry() call. In order to handle IOMMU unmaps, the proxy execution service will also register as a listener on the device's DMA address space. When an IOMMU memory region is created within the DMA address space, an IOMMU notifier for unmaps will be added to the memory region that will forward unmaps to the emulation process. This also will require a proxy_ctx_callbacks() call to register an IOMMU handler for incoming IOMMU requests from the emulation program. 2.3.6 device emulation process The device emulation process will run the object hierarchy of the device, hopefully unmodified. It will be based on the QEMU source code, because for anything but the simplest device, it would not be a tractable problem to re-implement both the object model and the many device backends that QEMU has. The parts of QEMU that the emulation program will need include the object model; the memory emulation objects; the device emulation objects of the targeted device, and any dependent devices; and, the device's backends. It will also need code to setup the machine environment, handle requests from the QEMU process, and route machine-level requests (such as interrupts or IOMMU mappings) back to the QEMU process. 2.3.6.1 initialization The process initialization sequence will follow the same sequence followed by QEMU. It will first initialize the backend objects, then device emulation objects. The JSON arrays sent by the QEMU process will drive which objects need to be created. 2.3.6.1.1 address spaces Before the device objects are created, the initial address spaces and memory regions must be configured with memory_map_init(). This creates a RAM memory region object (system_memory) and an IO memory region object (system_io). 2.3.6.1.2 RAM RAM memory region creation will follow how pc_memory_init() creates them, but must use memory_region_init_ram_from_fd() instead of memory_region_allocate_system_memory(). The file descriptors needed will be supplied by the guest memory table from above. Those RAM regions would then be added to the system_memory memory region with memory_region_add_subregion(). 2.3.6.1.3 PCI IO initialization will be driven by the JSON description sent from the QEMU process. For a PCI device, a PCI bus will need to be created with pci_root_bus_new(), and a PCI memory region will need to be created and added to the system_memory memory region with memory_region_add_subregion_overlap(). The overlap version is required for architectures where PCI memory overlaps with RAM memory. 2.3.6.2 MMIO handling The device emulation objects will use memory_region_init_io() to install their MMIO handlers, and pci_register_bar() to associate those handlers with a PCI BAR, as they do withing QEMU currently. In order to use address_space_rw() in the emulation process to handle MMIO requests from QEMU, the PCI physical addresses must be the same in the QEMU process and the device emulation process. In order to accomplish that, guest BAR programming must also be forwarded from QEMU to the emulation process. 2.3.6.3 interrupt injection When device emulation wants to inject an interrupt into the VM, the request climbs the device's bus object hierarchy until the point where a bus object knows how to signal the interrupt to the guest. The details depend on the type of interrupt being raised. 2.3.6.3.1 PCI pin interrupts On x86 systems, there is an emulated IOAPIC object attached to the root PCI bus object, and the root PCI object forwards interrupt requests to it. The IOAPIC object, in turn, calls the KVM driver to inject the corresponding interrupt into the VM. The simplest way to handle this in an emulation process would be to setup the root PCI bus driver (via pci_bus_irqs()) to send a interrupt request back to the QEMU process, and have the device proxy object reflect it up the PCI tree there. 2.3.6.3.2 PCI MSI/X interrupts PCI MSI/X interrupts are implemented in HW as DMA writes to a CPU-specific PCI address. In QEMU on x86, a KVM APIC object receives these DMA writes, then calls into the KVM driver to inject the interrupt into the VM. A simple emulation process implementation would be to send the MSI DMA address from QEMU as a message at initialization, then install an address space handler at that address which forwards the MSI message back to QEMU. 2.3.6.4 DMA operations When a emulation object wants to DMA into or out of guest memory, it first must use dma_memory_map() to convert the DMA address to a local virtual address. The emulation process memory region objects setup above will be used to translate the DMA address to a local virtual address the device emulation code can access. 2.3.6.5 IOMMU When an IOMMU is in use in QEMU, DMA translation uses IOMMU memory regions to translate the DMA address to a guest physical address before that physical address can be translated to a local virtual address. The emulation process will need similar functionality. 2.3.6.5.1 IOTLB cache The emulation process will maintain a cache of recent IOMMU translations (the IOTLB). When the translate() callback of an IOMMU memory region is invoked, the IOTLB cache will be searched for an entry that will map the DMA address to a guest PA. On a cache miss, a message will be sent back to QEMU requesting the corresponding translation entry, which be both be used to return a guest address and be added to the cache. 2.3.6.5.2 IOTLB purge The IOMMU emulation will also need to act on unmap requests from QEMU. These happen when the guest IOMMU driver purges an entry from the guest's translation table. 2.4 Accelerating device emulation The messages that are required to be sent between QEMU and the emulation process can add considerable latency to IO operations. The optimizations described below attempt to ameliorate this effect by allowing the emulation process to communicate directly with the kernel KVM driver. The KVM file descriptors created wold be passed to the emulation process via initialization messages, much like the guest memory table is done. 2.4.1 MMIO acceleration Vhost user applications can receive guest virtio driver stores directly from KVM. The issue with the eventfd mechanism used by vhost user is that it does not pass any data with the event indication, so it cannot handle guest loads or guest stores that carry store data. This concept could, however, be expanded to cover more cases. The expanded idea would require a new type of KVM device: KVM_DEV_TYPE_USER. This device has two file descriptors: a master descriptor that QEMU can use for configuration, and a slave descriptor that the emulation process can use to receive MMIO notifications. QEMU would create both descriptors using the KVM driver, and pass the slave descriptor to the emulation process via an initialization message. 2.4.1.1 data structures 2.4.1.1.1 guest physical range The guest physical range structure describes the address range that a device will respond to. It includes the base and length of the range, as well as which bus the range resides on (e.g., on an x86 machine, it can specify whether the range refers to memory or IO addresses). A device can have multiple physical address ranges it responds to (e.g., a PCI device can have multiple BARs), so the structure will also include an enumeration value to specify which of the device's ranges is being referred to. 2.4.1.1.2 MMIO request structure This structure describes an MMIO operation. It includes which guest physical range the MMIO was within, the offset within that range, the MMIO type (e.g., load or store), and its length and data. It also includes a sequence number that can be used to reply to the MMIO, and the CPU that issued the MMIO. 2.4.1.1.3 MMIO request queues MMIO request queues are FIFO arrays of MMIO request structures. There are two queues: pending queue is for MMIOs that haven't been read by the emulation program, and the sent queue is for MMIOs that haven't been acknowledged. The main use of the second queue is to validate MMIO replies from the emulation program. 2.4.1.1.4 scoreboard Each CPU in the VM is emulated in QEMU by a separate thread, so multiple MMIOs may be waiting to be consumed by an emulation program and multiple threads may be waiting for MMIO replies. The scoreboard would contain a wait queue and sequence number for the per-CPU threads, allowing them to be individually woken when the MMIO reply is received from the emulation program. It also tracks the number of posted MMIO stores to the device that haven't been replied to, in order to satisfy the PCI constraint that a load to a device will not complete until all previous stores to that device have been completed. 2.4.1.1.5 device shadow memory Some MMIO loads do not have device side-effects. These MMIOs can be completed without sending a MMIO request to the emulation program if the emulation program shares a shadow image of the device's memory image with the KVM driver. The emulation program will ask the KVM driver to allocate memory for the shadow image, and will then use mmap() to directly access it. The emulation program can control KVM access to the shadow image by sending KVM an access map telling it which areas of the image have no side-effects (and can be completed immediately), and which require a MMIO request to the emulation program. The access map can also inform the KVM drive which size accesses are allowed to the image. 2.4.1.2 master descriptor The master descriptor is used by QEMU to configure the new KVM device. The descriptor would be returned by the KVM driver when QEMU issues a KVM_CREATE_DEVICE ioctl() with a KVM_DEV_TYPE_USER type. 2.4.1.2.1 KVM_DEV_TYPE_USER device ops The KVM_DEV_TYPE_USER operations vector will be registered by a kvm_register_device_ops() call when the KVM system in initialized by kvm_init(). These device ops are called by the KVM driver when QEMU executes certain ioctls() on its KVM file descriptor. They include: 2.4.1.1.2.1 create This routine is called when QEMU issues a KVM_CREATE_DEVICE ioctl() on its per-VM file descriptor. It will allocate and initialize a KVM user device specific data structure, and assign the kvm_device private field to it. 2.4.1.1.2.2 ioctl This routine is invoked when QEMU issues an ioctl() on the master descriptor. The ioctl() commands supported are defined by the KVM device type. KVM_DEV_TYPE_USER ones will need several commands: KVM_DEV_USER_SLAVE_FD creates the slave file descriptor that will be passed to the device emulation program. Only one slave can be created by each master descriptor. The file operations performed by this descriptor are described below. The KVM_DEV_USER_PA_RANGE command configures a guest physical address range that the slave descriptor will receive MMIO notifications for. The range is specified by a guest physical range structure argument. For buses that assign addresses to devices dynamically, this command can be executed while the guest is running, such as the case when a guest changes a device's PCI BAR registers. KVM_DEV_USER_PA_RANGE will use kvm_io_bus_register_dev() to register kvm_io_device_ops callbacks to be invoked when the guest performs a MMIO operation within the range. When a range is changed, kvm_io_bus_unregister_dev() is used to remove the previous instantiation. KVM_DEV_USER_TIMEOUT will configure a timeout value that specifies how long KVM will wait for the emulation process to respond to a MMIO indication. 2.4.1.1.2.3 destroy This routine is called when the VM instance is destroyed. It will need to destroy the slave descriptor; and free any memory allocated by the driver, as well as the kvm_device structure itself. 2.4.1.3 slave descriptor The slave descriptor will have its own file operations vector, which responds to system calls on the descriptor performed by the device emulation program. 2.4.1.3.1 read A read returns any pending MMIO requests from the KVM driver as MMIO request structures. Multiple structures can be returned if there are multiple MMIO operations pending. The MMIO requests are moved from the pending queue to the sent queue, and if there are threads waiting for space in the pending to add new MMIO operations, they will be woken here. 2.4.1.3.2 write A write also consists of a set of MMIO requests. They are compared to the MMIO requests in the sent queue. Matches are removed from the sent queue, and any threads waiting for the reply are woken. If a store is removed, then the number of posted stores in the per-CPU scoreboard is decremented. When the number is zero, and a non side-effect load was waiting for posted stores to complete, the load is continued. 2.4.1.3.3 ioctl There are several ioctl()s that can be performed on the slave descriptor. A KVM_DEV_USER_SHADOW_SIZE ioctl() causes the KVM driver to allocate memory for the shadow image. This memory can later be mmap()ed by the emulation process to share the emulation's view of device memory with the KVM driver. A KVM_DEV_USER_SHADOW_CTRL ioctl() controls access to the shadow image. It will send the KVM driver a shadow control map, which specifies which areas of the image can complete guest loads without sending the load request to the emulation program. It will also specify the size of load operations that are allowed. 2.4.1.3.4 poll An emulation program will use the poll() call with a POLLIN flag to determine if there are MMIO requests waiting to be read. It will return if the pending MMIO request queue is not empty. 2.4.1.3.5 mmap This call allows the emulation program to directly access the shadow image allocated by the KVM driver. As device emulation updates device memory, changes with no side-effects will be reflected in the shadow, and the KVM driver can satisfy guest loads from the shadow image without needing to wait for the emulation program. 2.4.1.4 kvm_io_device ops Each KVM per-CPU thread can handle MMIO operation on behalf of the guest VM. KVM will use the MMIO's guest physical address to search for a matching kvm_io_devce to see if the MMIO can be handled by the KVM driver instead of exiting back to QEMU. If a match is found, the corresponding callback will be invoked. 2.4.1.4.1 read This callback is invoked when the guest performs a load to the device. Loads with side-effects must be handled synchronously, with the KVM driver putting the QEMU thread to sleep waiting for the emulation process reply before re-starting the guest. Loads that do not have side-effects may be optimized by satisfying them from the shadow image, if there are no outstanding stores to the device by this CPU. PCI memory ordering demands that a load cannot complete before all older stores to the same device have been completed. 2.4.1.4.2 write Stores can be handled asynchronously unless the pending MMIO request queue is full. In this case, the QEMU thread must sleep waiting for space in the queue. Stores will increment the number of posted stores in the per-CPU scoreboard, in order to implement the PCI ordering constraint above. 2.4.2 interrupt acceleration This performance optimization would work much like a vhost user application does, where the QEMU process sets up eventfds that cause the device's corresponding interrupt to be triggered by the KVM driver. These irq file descriptors are sent to the emulation process at initialization, and are used when the emulation code raises a device interrupt. 2.4.2.1 intx acceleration Traditional PCI pin interrupts are level based, so, in addition to an irq file descriptor, a re-sampling file descriptor needs to be sent to the emulation program. This second file descriptor allows multiple devices sharing an irq to be notified when the interrupt has been acknowledged by the guest, so they can re-trigger the interrupt if their device has not de-asserted it. 2.4.2.1.1 intx irq descriptor The irq descriptors are created by the proxy object using event_notifier_init() to create the irq and re-sampling eventds, and kvm_vm_ioctl(KVM_IRQFD) to bind them to an interrupt. The interrupt route can be found with pci_device_route_intx_to_irq(). 2.4.2.1.2 intx routing changes Intx routing can be changed when the guest programs the APIC the device pin is connected to. The proxy object in QEMU will use pci_device_set_intx_routing_notifier() to be informed of any guest changes to the route. This handler will broadly follow the VFIO interrupt logic to change the route: de-assigning the existing irq descriptor from its route, then assigning it the new route. (see vfio_intx_update()) 2.4.2.2 MSI/X acceleration MSI/X interrupts are sent as DMA transactions to the host. The interrupt data contains a vector that is programed by the guest, A device may have multiple MSI interrupts associated with it, so multiple irq descriptors may need to be sent to the emulation program. 2.4.2.2.1 MSI/X irq descriptor This case will also follow the VFIO example. For each MSI/X interrupt, an eventfd is created, a virtual interrupt is allocated by kvm_irqchip_add_msi_route(), and the virtual interrupt is bound to the eventfd with kvm_irqchip_add_irqfd_notifier(). 2.4.2.2.2 MSI/X config space changes The guest may dynamically update several MSI-related tables in the device's PCI config space. These include per-MSI interrupt enables and vector data. Additionally, MSIX tables exist in device memory space, not config space. Much like the BAR case above, the proxy object must look at guest config space programming to keep the MSI interrupt state consistent between QEMU and the emulation program. 3. Disaggregated CPU emulation After IO services have been disaggregated, a second phase would be to separate a process to handle CPU instruction emulation from the main QEMU control function. There are no object separation points for this code, so the first task would be to create one. 4. Host access controls Separating QEMU relies on the host OS's access restriction mechanisms to enforce that the differing processes can only access the objects they are entitled to. There are a couple types of mechanisms usually provided by general purpose OSs. 4.1 Discretionary access control Discretionary access control allows each user to control who can access their files. In Linux, this type of control is usually too coarse for QEMU separation, since it only provides three separate access controls: one for the same user ID, the second for users IDs with the same group ID, and the third for all other user IDs. Each device instance would need a separate user ID to provide access control, which is likely to be unwieldy for dynamically created VMs. 4.2 Mandatory access control Mandatory access control allows the OS to add an additional set of controls on top of discretionary access for the OS to control. It also adds other attributes to processes and files such as types, roles, and categories, and can establish rules for how processes and files can interact. 4.2.1 Type enforcement Type enforcement assigns a 'type' attribute to processes and files, and allows rules to be written on what operations a process with a given type can perform on a file with a given type. QEMU separation could take advantage of type enforcement by running the emulation processes with different types, both from the main QEMU process, and from the emulation processes of different classes of devices. For example, guest disk images and disk emulation processes could have types separate from the main QEMU process and non-disk emulation processes, and the type rules could prevent processes other than disk emulation ones from accessing guest disk images. Similarly, network emulation processes can have a type separate from the main QEMU process and non-network emulation process, and only that type can access the host tun/tap device used to provide guest networking. 4.2.2 Category enforcement Category enforcement assigns a set of numbers within a given range to the process or file. The process is granted access to the file if the process's set is a superset of the file's set. This enforcement can be used to separate multiple instances of devices in the same class. For example, if there are multiple disk devices provides to a guest, each device emulation process could be provisioned with a separate category. The different device emulation processes would not be able to access each other's backing disk images. Alternatively, categories could be used in lieu of the type enforcement scheme described above. In this scenario, different categories would be used to prevent device emulation processes in different classes from accessing resources assigned to other classes. Elena Ufimtseva (1): multi-process QEMU: introduce proxy object Jagannathan Raman (7): multi-process QEMU: build system for remote device process multi-process QEMU: define proxy-link object multi-process QEMU: setup PCI host bridge for remote device multi-process QEMU: setup a machine for remote device process multi-process QEMU: setup memory manager for remote device multi-process QEMU: remote process initialization multi-process QEMU: synchronize RAM between QEMU & remote device Makefile | 4 +- Makefile.objs | 20 +++ Makefile.target | 42 ++++- accel/stubs/kvm-stub.c | 5 + accel/stubs/tcg-stub.c | 81 +++++++++ backends/Makefile.objs | 2 + block/Makefile.objs | 2 + exec.c | 3 +- hw/Makefile.objs | 8 + hw/block/Makefile.objs | 2 + hw/core/Makefile.objs | 14 ++ hw/nvram/Makefile.objs | 2 + hw/pci/Makefile.objs | 4 + hw/qemu-proxy.c | 371 ++++++++++++++++++++++++++++++++++++++++++ hw/scsi/Makefile.objs | 3 + hw/scsi/qemu-scsi-dev.c | 125 ++++++++++++++ include/exec/address-spaces.h | 2 + include/glib-compat.h | 4 + include/hw/qemu-proxy.h | 59 +++++++ include/io/proxy-link.h | 112 +++++++++++++ include/remote/machine.h | 43 +++++ include/remote/memory.h | 34 ++++ include/remote/pcihost.h | 58 +++++++ io/Makefile.objs | 1 + io/proxy-link.c | 263 ++++++++++++++++++++++++++++++ migration/Makefile.objs | 2 + qom/Makefile.objs | 4 + remote/Makefile.objs | 3 + remote/machine.c | 78 +++++++++ remote/memory.c | 93 +++++++++++ remote/pcihost.c | 84 ++++++++++ stubs/monitor.c | 25 +++ stubs/net-stub.c | 31 ++++ stubs/replay.c | 14 ++ stubs/vl-stub.c | 79 +++++++++ stubs/vmstate.c | 20 +++ 36 files changed, 1693 insertions(+), 4 deletions(-) create mode 100644 hw/qemu-proxy.c create mode 100644 hw/scsi/qemu-scsi-dev.c create mode 100644 include/hw/qemu-proxy.h create mode 100644 include/io/proxy-link.h create mode 100644 include/remote/machine.h create mode 100644 include/remote/memory.h create mode 100644 include/remote/pcihost.h create mode 100644 io/proxy-link.c create mode 100644 remote/Makefile.objs create mode 100644 remote/machine.c create mode 100644 remote/memory.c create mode 100644 remote/pcihost.c create mode 100644 stubs/net-stub.c create mode 100644 stubs/vl-stub.c