On 7/30/2020 1:49 PM, Dr. David Alan Gilbert wrote:
> * Steve Sistare (steven.sist...@oracle.com) wrote:
>> Improve and extend the qemu functions that save and restore VM state so a
>> guest may be suspended and resumed with minimal pause time. qemu may be
>> updated to a new version in between.
>
> Nice.
>
>> The first set of patches adds the cprsave and cprload commands to save and
>> restore VM state, and allow the host kernel to be updated and rebooted in
>> between. The VM must create guest RAM in a persistent shared memory file,
>> such as /dev/dax0.0 or persistant /dev/shm PKRAM as proposed in
>> https://lore.kernel.org/lkml/1588812129-8596-1-git-send-email-anthony.yzn...@oracle.com/
>>
>> cprsave stops the VCPUs and saves VM device state in a simple file, and
>> thus supports any type of guest image and block device. The caller must
>> not modify the VM's block devices between cprsave and cprload.
>
> can I ask why you don't just add a migration flag to skip the devices
> you don't want, and then do a migrate to a file?
> (i.e. migrate "exec:cat > afile")
> We already have the 'x-ignore-shared' capability that's used for doing
> RAM snapshots of VMs; primarily I think for being able to start a VM
> from a RAM snapshot as a fast VM start trick.
> (There's also a xen_save_devices that does something similar).
> If you backed the RAM as you say, enabled x-ignore-shared and then did:
>
> migrate "exec:cat > afile"
>
> and restarted the destination with:
>
> migrate_incoming "exec:cat afile"
>
> what is different (except the later stuff about the vfio magic and
> chardevs).
>
> Dave
Yes, I did consider whether to extend the migration syntax and implemention in
save_vmstate and load_vmstate, versus creating something new. Those functions
handle stuff like bdrv snapshot, aio, and migration which are n/a for the cpr
use case, and the cpr functions handle state that is n/a for the migration
case.
I judged that a single function handling both would be less readable and
maintainable. At their core all these routines call qemu_loadvm_state() and
qemu_savevm_state().
The surrounding code is mostly different.
Take a look at
savevm.c:save_vmstate() vs save_cpr_snapshot() attached
and
savevm.c:load_vmstate() vs load_cpr_snapshot() attached
I attached the complete versions of the cpr functions because they are built up
over multiple patches in this series, thus hard to visualize in patch form.
- Steve
>
>> cprsave and cprload support guests with vfio devices if the caller first
>> suspends the guest by issuing guest-suspend-ram to the qemu guest agent.
>> The guest drivers suspend methods flush outstanding requests and re-
>> initialize the devices, and thus there is no device state to save and
>> restore.
>>
>> 1 savevm: add vmstate handler iterators
>> 2 savevm: VM handlers mode mask
>> 3 savevm: QMP command for cprsave
>> 4 savevm: HMP Command for cprsave
>> 5 savevm: QMP command for cprload
>> 6 savevm: HMP Command for cprload
>> 7 savevm: QMP command for cprinfo
>> 8 savevm: HMP command for cprinfo
>> 9 savevm: prevent cprsave if memory is volatile
>> 10 kvmclock: restore paused KVM clock
>> 11 cpu: disable ticks when suspended
>> 12 vl: pause option
>> 13 gdbstub: gdb support for suspended state
>>
>> The next patches add a restart method that eliminates the persistent memory
>> constraint, and allows qemu to be updated across the restart, but does not
>> allow host reboot. Anonymous memory segments used by the guest are
>> preserved across a re-exec of qemu, mapped at the same VA, via a proposed
>> madvise(MADV_DOEXEC) option in the Linux kernel. See
>> https://lore.kernel.org/lkml/1595869887-23307-1-git-send-email-anthony.yzn...@oracle.com/
>>
>> 14 savevm: VMS_RESTART and cprsave restart
>> 15 vl: QEMU_START_FREEZE env var
>> 16 oslib: add qemu_clr_cloexec
>> 17 util: env var helpers
>> 18 osdep: import MADV_DOEXEC
>> 19 memory: ram_block_add cosmetic changes
>> 20 vl: add helper to request re-exec
>> 21 exec, memory: exec(3) to restart
>> 22 char: qio_channel_socket_accept reuse fd
>> 23 char: save/restore chardev socket fds
>> 24 ui: save/restore vnc socket fds
>> 25 char: save/restore chardev pty fds
>> 26 monitor: save/restore QMP negotiation status
>> 27 vhost: reset vhost devices upon cprsave
>> 28 char: restore terminal on restart
>>
>> The next patches extend the restart method to save and restore vfio-pci
>> state, eliminating the requirement for a guest agent. The vfio container,
>> group, and device descriptors are preserved across the qemu re-exec.
>>
>> 29 pci: export pci_update_mappings
>> 30 vfio-pci: save and restore
>> 31 vfio-pci: trace pci config
>> 32 vfio-pci: improved tracing
>>
>> Here is an example of updating qemu from v4.2.0 to v4.2.1 using
>> "cprload restart". The software update is performed while the guest is
>> running to minimize downtime.
>>
>> window 1 | window 2
>> |
>> # qemu-system-x86_64 ... |
>> QEMU 4.2.0 monitor - type 'help' ... |
>> (qemu) info status |
>> VM status: running |
>> | # yum update qemu
>> (qemu) cprsave /tmp/qemu.sav restart |
>> QEMU 4.2.1 monitor - type 'help' ... |
>> (qemu) info status |
>> VM status: paused (prelaunch) |
>> (qemu) cprload /tmp/qemu.sav |
>> (qemu) info status |
>> VM status: running |
>>
>>
>> Here is an example of updating the host kernel using "cprload reboot"
>>
>> window 1 | window 2
>> |
>> # qemu-system-x86_64 ...mem-path=/dev/dax0.0 ...|
>> QEMU 4.2.1 monitor - type 'help' ... |
>> (qemu) info status |
>> VM status: running |
>> | # yum update kernel-uek
>> (qemu) cprsave /tmp/qemu.sav restart |
>> |
>> # systemctl kexec |
>> kexec_core: Starting new kernel |
>> ... |
>> |
>> # qemu-system-x86_64 ...mem-path=/dev/dax0.0 ...|
>> QEMU 4.2.1 monitor - type 'help' ... |
>> (qemu) info status |
>> VM status: paused (prelaunch) |
>> (qemu) cprload /tmp/qemu.sav |
>> (qemu) info status |
>> VM status: running |
>>
>>
>> Mark Kanda (5):
>> char: qio_channel_socket_accept reuse fd
>> char: save/restore chardev socket fds
>> ui: save/restore vnc socket fds
>> monitor: save/restore QMP negotiation status
>> vhost: reset vhost devices upon cprsave
>>
>> Steve Sistare (27):
>> savevm: add vmstate handler iterators
>> savevm: VM handlers mode mask
>> savevm: QMP command for cprsave
>> savevm: HMP Command for cprsave
>> savevm: QMP command for cprload
>> savevm: HMP Command for cprload
>> savevm: QMP command for cprinfo
>> savevm: HMP command for cprinfo
>> savevm: prevent cprsave if memory is volatile
>> kvmclock: restore paused KVM clock
>> cpu: disable ticks when suspended
>> vl: pause option
>> gdbstub: gdb support for suspended state
>> savevm: VMS_RESTART and cprsave restart
>> vl: QEMU_START_FREEZE env var
>> oslib: add qemu_clr_cloexec
>> util: env var helpers
>> osdep: import MADV_DOEXEC
>> memory: ram_block_add cosmetic changes
>> vl: add helper to request re-exec
>> exec, memory: exec(3) to restart
>> char: save/restore chardev pty fds
>> char: restore terminal on restart
>> pci: export pci_update_mappings
>> vfio-pci: save and restore
>> vfio-pci: trace pci config
>> vfio-pci: improved tracing
>>
>> MAINTAINERS | 7 ++
>> accel/kvm/kvm-all.c | 8 +-
>> accel/kvm/trace-events | 3 +-
>> chardev/char-pty.c | 38 +++++--
>> chardev/char-socket.c | 35 ++++++
>> chardev/char-stdio.c | 7 ++
>> chardev/char.c | 16 +++
>> exec.c | 88 +++++++++++++--
>> gdbstub.c | 11 +-
>> hmp-commands.hx | 46 ++++++++
>> hw/i386/kvm/clock.c | 6 +-
>> hw/pci/msix.c | 1 +
>> hw/pci/pci.c | 17 +--
>> hw/pci/trace-events | 5 +-
>> hw/vfio/common.c | 115 ++++++++++++++++----
>> hw/vfio/pci.c | 179 ++++++++++++++++++++++++++++++-
>> hw/vfio/platform.c | 2 +-
>> hw/vfio/trace-events | 11 +-
>> hw/virtio/vhost.c | 12 +++
>> include/chardev/char.h | 8 ++
>> include/exec/memory.h | 4 +
>> include/hw/pci/pci.h | 2 +
>> include/hw/vfio/vfio-common.h | 4 +-
>> include/io/channel-socket.h | 3 +-
>> include/migration/register.h | 3 +
>> include/migration/vmstate.h | 11 ++
>> include/monitor/hmp.h | 3 +
>> include/qemu/cutils.h | 1 +
>> include/qemu/env.h | 31 ++++++
>> include/qemu/osdep.h | 8 ++
>> include/sysemu/sysemu.h | 10 ++
>> io/channel-socket.c | 12 ++-
>> io/net-listener.c | 4 +-
>> migration/block.c | 1 +
>> migration/migration.c | 4 +-
>> migration/ram.c | 1 +
>> migration/savevm.c | 237
>> ++++++++++++++++++++++++++++++++++++-----
>> migration/savevm.h | 4 +-
>> monitor/hmp-cmds.c | 28 +++++
>> monitor/qmp-cmds.c | 16 +++
>> monitor/qmp.c | 42 ++++++++
>> qapi/migration.json | 35 ++++++
>> qapi/pragma.json | 1 +
>> qemu-options.hx | 9 ++
>> scsi/qemu-pr-helper.c | 2 +-
>> softmmu/vl.c | 65 ++++++++++-
>> tests/qtest/tpm-emu.c | 2 +-
>> tests/test-char.c | 2 +-
>> tests/test-io-channel-socket.c | 4 +-
>> trace-events | 2 +
>> ui/vnc.c | 153 +++++++++++++++++++++-----
>> util/Makefile.objs | 2 +-
>> util/env.c | 132 +++++++++++++++++++++++
>> util/oslib-posix.c | 9 ++
>> util/oslib-win32.c | 4 +
>> 55 files changed, 1331 insertions(+), 135 deletions(-)
>> create mode 100644 include/qemu/env.h
>> create mode 100644 util/env.c
>>
>> --
>> 1.8.3.1
>>
>>
> --
> Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
>
void save_cpr_snapshot(const char *file, const char *mode, Error **errp)
{
int ret = 0;
QEMUFile *f;
VMStateMode op;
if (!strcmp(mode, "reboot")) {
op = VMS_REBOOT;
} else if (!strcmp(mode, "restart")) {
op = VMS_RESTART;
} else {
error_setg(errp, "cprsave: bad mode %s", mode);
return;
}
if (op == VMS_REBOOT && qemu_ram_volatile(errp)) {
return;
}
if (op == VMS_RESTART && QEMU_MADV_DOEXEC == QEMU_MADV_INVALID) {
error_setg(errp, "kernel does not support MADV_DOEXEC.");
return;
}
if (op == VMS_RESTART && xen_enabled()) {
error_setg(errp, "xen does not support cprsave restart");
return;
}
f = qf_file_open(file, O_CREAT | O_WRONLY | O_TRUNC, 0600, errp);
if (!f) {
return;
}
ret = global_state_store();
if (ret) {
error_setg(errp, "Error saving global state");
qemu_fclose(f);
return;
}
/* Update timers_state before saving. Suspend did not so do. */
if (runstate_check(RUN_STATE_SUSPENDED)) {
cpu_disable_ticks();
}
vm_stop(RUN_STATE_SAVE_VM);
ret = qemu_savevm_state(f, op, errp);
if ((ret < 0) && !*errp) {
error_setg(errp, "qemu_savevm_state failed");
}
qemu_fclose(f);
if (op == VMS_REBOOT) {
no_shutdown = 0;
qemu_system_shutdown_request();
} else if (op == VMS_RESTART) {
if (qemu_preserve_ram(errp)) {
return;
}
save_chardev_fds();
save_vnc_fds();
save_named_fd("mntfd"); /* was received from qemu-cpr */
save_named_fd("ctlfd"); /* was received from qemu-cpr */
walkenv(FD_PREFIX, preserve_fd, 0);
reset_vhost_devices();
save_qmp_negotiation_status();
qemu_term_exit();
qemu_system_exec_request();
putenv((char *)"QEMU_START_FREEZE=");
}
}
void load_cpr_snapshot(const char *file, Error **errp)
{
QEMUFile *f;
int ret;
RunState state;
if (runstate_is_running()) {
error_setg(errp, "cprload called for a running VM");
return;
}
f = qf_file_open(file, O_RDONLY, 0, errp);
if (!f) {
return;
}
ret = qemu_loadvm_state(f, VMS_REBOOT | VMS_RESTART);
qemu_fclose(f);
if (ret < 0) {
error_setg(errp, "Error %d while loading VM state", ret);
return;
}
state = global_state_get_runstate();
if (state == RUN_STATE_RUNNING) {
vm_start();
} else {
runstate_set(state);
if (runstate_check(RUN_STATE_SUSPENDED)) {
start_on_wake = 1;
}
}
load_vnc_fds();
}
