Steve Sistare <steven.sist...@oracle.com> writes: > Add documentation for the cpr-transfer migration mode. > > Signed-off-by: Steve Sistare <steven.sist...@oracle.com> > Reviewed-by: Peter Xu <pet...@redhat.com> > --- > docs/devel/migration/CPR.rst | 182 > ++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 180 insertions(+), 2 deletions(-) > > diff --git a/docs/devel/migration/CPR.rst b/docs/devel/migration/CPR.rst > index 63c3647..d6021d5 100644 > --- a/docs/devel/migration/CPR.rst > +++ b/docs/devel/migration/CPR.rst > @@ -5,7 +5,7 @@ CPR is the umbrella name for a set of migration modes in > which the > VM is migrated to a new QEMU instance on the same host. It is > intended for use when the goal is to update host software components > that run the VM, such as QEMU or even the host kernel. At this time, > -cpr-reboot is the only available mode. > +the cpr-reboot and cpr-transfer modes are available. > > Because QEMU is restarted on the same host, with access to the same > local devices, CPR is allowed in certain cases where normal migration > @@ -53,7 +53,7 @@ RAM is copied to the migration URI. > Outgoing: > * Set the migration mode parameter to ``cpr-reboot``. > * Set the ``x-ignore-shared`` capability if desired. > - * Issue the ``migrate`` command. It is recommended the the URI be a > + * Issue the ``migrate`` command. It is recommended the URI be a > ``file`` type, but one can use other types such as ``exec``, > provided the command captures all the data from the outgoing side, > and provides all the data to the incoming side. > @@ -145,3 +145,181 @@ Caveats > > cpr-reboot mode may not be used with postcopy, background-snapshot, > or COLO. > + > +cpr-transfer mode > +----------------- > + > +This mode allows the user to transfer a guest to a new QEMU instance > +on the same host with minimal guest pause time, by preserving guest > +RAM in place, albeit with new virtual addresses in new QEMU. Devices > +and their pinned memory pages will also be preserved in a future QEMU > +release. > + > +The user starts new QEMU on the same host as old QEMU, with command- > +line arguments to create the same machine, plus the ``-incoming`` > +option for the main migration channel, like normal live migration. > +In addition, the user adds a second -incoming option with channel > +type ``cpr``. This CPR channel must support file descriptor transfer > +with SCM_RIGHTS, i.e. it must be a UNIX domain socket. > + > +To initiate CPR, the user issues a migrate command to old QEMU, > +adding a second migration channel of type ``cpr`` in the channels > +argument. Old QEMU stops the VM, saves state to the migration > +channels, and enters the postmigrate state. Execution resumes in > +new QEMU. > + > +New QEMU reads the CPR channel before opening a monitor, hence > +the CPR channel cannot be specified in the list of channels for a > +migrate-incoming command. It may only be specified on the command > +line. > + > +Usage > +^^^^^ > + > +Memory backend objects must have the ``share=on`` attribute. > + > +The VM must be started with the ``-machine aux-ram-share=on`` > +option. This causes implicit RAM blocks (those not described by > +a memory-backend object) to be allocated by mmap'ing a memfd. > +Examples include VGA and ROM. > + > +Outgoing: > + * Set the migration mode parameter to ``cpr-transfer``. > + * Issue the ``migrate`` command, containing a main channel and > + a cpr channel. > + > +Incoming: > + * Start new QEMU with two ``-incoming`` options. > + * If the VM was running when the outgoing ``migrate`` command was > + issued, then QEMU automatically resumes VM execution. > + > +Caveats > +^^^^^^^ > + > +cpr-transfer mode may not be used with postcopy, background-snapshot, > +or COLO. > + > +memory-backend-epc is not supported. > + > +The main incoming migration channel address cannot be a file type. > + > +If the main incoming channel address is an inet socket, then the port > +cannot be 0 (meaning dynamically choose a port). > + > +When using ``-incoming defer``, you must issue the migrate command to > +old QEMU before issuing any monitor commands to new QEMU, because new > +QEMU blocks waiting to read from the cpr channel before starting its > +monitor, and old QEMU does not write to the channel until the migrate > +command is issued. However, new QEMU does not open and read the > +main migration channel until you issue the migrate incoming command. > + > +Example 1: incoming channel > +^^^^^^^^^^^^^^^^^^^^^^^^^^^ > + > +In these examples, we simply restart the same version of QEMU, but > +in a real scenario one would start new QEMU on the incoming side. > +Note that new QEMU does not print the monitor prompt until old QEMU > +has issued the migrate command. The outgoing side uses QMP because > +HMP cannot specify a CPR channel. Some QMP responses are omitted for > +brevity. > + > +:: > + > + Outgoing: Incoming: > + > + # qemu-kvm -qmp stdio > + -object memory-backend-file,id=ram0,size=4G, > + mem-path=/dev/shm/ram0,share=on -m 4G > + -machine aux-ram-share=on > + ... > + # qemu-kvm -monitor stdio > + -incoming tcp:0:44444 > + -incoming '{"channel-type": "cpr", > + "addr": { "transport": "socket", > + "type": "unix", "path": > "cpr.sock"}}' > + ...
I'm attempting this and not having much success. Surely I'm missing something: $ qemu-system-x86_64 -cpu host -smp 16 -machine pc,accel=kvm \ -drive id=drive0,if=none,format=qcow2,file=img.qcow2 \ -device virtio-blk-pci,id=image1,drive=drive0,bootindex=0 \ -qmp unix:./dst-qmp.sock,server,wait=off \ -nographic -serial mon:stdio \ -object memory-backend-file,id=ram0,size=4G,mem-path=/dev/shm/ram0,share=on \ -m 4G -machine aux-ram-share=on \ -incoming tcp:0:44444 \ -incoming '{"channel-type": "cpr", "addr": { "transport": "socket", "type": "unix", "path": "cpr.sock"}}' \ -trace loadvm_* -trace cpr_* -trace migration_* -trace migrate_* -trace qemu_loadvm_* cpr_transfer_input cpr.sock cpr_state_load cpr-transfer mode cpr_find_fd pc.bios, id 0 returns 15 cpr_find_fd pc.rom, id 0 returns 14 cpr_find_fd 0000:00:02.0/vga.vram, id 0 returns 13 cpr_find_fd 0000:00:02.0/vga.rom, id 0 returns 12 cpr_find_fd 0000:00:03.0/e1000.rom, id 0 returns 11 cpr_find_fd /rom@etc/acpi/tables, id 0 returns 10 cpr_find_fd /rom@etc/table-loader, id 0 returns 8 cpr_find_fd /rom@etc/acpi/rsdp, id 0 returns 3 migrate_set_state new state setup migration_socket_incoming_accepted migration_set_incoming_channel ioc=0x564dc31e7000 ioctype=qio-channel-socket migrate_set_state new state active loadvm_state_setup qemu_loadvm_state_section 1 qemu_loadvm_state_section_startfull 2(ram) 0 4 qemu_loadvm_state_section 3 qemu_loadvm_state_section_partend 2 qemu_loadvm_state_section 4 qemu_loadvm_state_section_startfull 0(timer) 0 2 qemu_loadvm_state_section 4 qemu_loadvm_state_section_startfull 1(slirp) 0 4 qemu_loadvm_state_section 4 qemu_loadvm_state_section_startfull 4(cpu_common) 0 1 qemu_loadvm_state_section 4 qemu_loadvm_state_section_startfull 5(cpu) 0 12 qemu_loadvm_state_section 4 qemu_loadvm_state_section_startfull 6(kvm-tpr-opt) 0 1 qemu-system-x86_64: error while loading state for instance 0x0 of device 'kvm-tpr-opt' qemu_loadvm_state_post_main -1 migrate_set_state new state failed migrate_error error=load of migration failed: Operation not permitted loadvm_state_cleanup qemu-system-x86_64: load of migration failed: Operation not permitted > + {"execute":"qmp_capabilities"} > + > + {"execute": "query-status"} > + {"return": {"status": "running", > + "running": true}} > + > + {"execute":"migrate-set-parameters", > + "arguments":{"mode":"cpr-transfer"}} > + > + {"execute": "migrate", "arguments": { "channels": [ > + {"channel-type": "main", > + "addr": { "transport": "socket", "type": "inet", > + "host": "0", "port": "44444" }}, > + {"channel-type": "cpr", > + "addr": { "transport": "socket", "type": "unix", > + "path": "cpr.sock" }}]}} > + > + QEMU 10.0.50 monitor > + (qemu) info status > + VM status: running > + > + {"execute": "query-status"} > + {"return": {"status": "postmigrate", > + "running": false}} > + > +Example 2: incoming defer > +^^^^^^^^^^^^^^^^^^^^^^^^^ > + > +This example uses ``-incoming defer`` to hot plug a device before > +accepting the main migration channel. Again note you must issue the > +migrate command to old QEMU before you can issue any monitor > +commands to new QEMU. > + > + > +:: > + > + Outgoing: Incoming: > + > + # qemu-kvm -monitor stdio > + -object memory-backend-file,id=ram0,size=4G, > + mem-path=/dev/shm/ram0,share=on -m 4G > + -machine aux-ram-share=on > + ... > + # qemu-kvm -monitor stdio > + -incoming defer > + -incoming '{"channel-type": "cpr", > + "addr": { "transport": "socket", > + "type": "unix", "path": > "cpr.sock"}}' > + ... > + {"execute":"qmp_capabilities"} > + > + {"execute": "device_add", > + "arguments": {"driver": "pcie-root-port"}} > + > + {"execute":"migrate-set-parameters", > + "arguments":{"mode":"cpr-transfer"}} > + > + {"execute": "migrate", "arguments": { "channels": [ > + {"channel-type": "main", > + "addr": { "transport": "socket", "type": "inet", > + "host": "0", "port": "44444" }}, > + {"channel-type": "cpr", > + "addr": { "transport": "socket", "type": "unix", > + "path": "cpr.sock" }}]}} > + > + QEMU 10.0.50 monitor > + (qemu) info status > + VM status: paused (inmigrate) > + (qemu) device_add pcie-root-port > + (qemu) migrate_incoming tcp:0:44444 > + (qemu) info status > + VM status: running > + > + {"execute": "query-status"} > + {"return": {"status": "postmigrate", > + "running": false}} > + > +Futures > +^^^^^^^ > + > +cpr-transfer mode is based on a capability to transfer open file > +descriptors from old to new QEMU. In the future, descriptors for > +vfio, iommufd, vhost, and char devices could be transferred, > +preserving those devices and their kernel state without interruption, > +even if they do not explicitly support live migration.