Re: [PATCH V6 00/27] Live Update

[Steven Sistare <steven.sistare@oracle.com>]

I forgot to mention in the changes list: I added a new mechanism to save fd values,
in lieu of the environment.  See [PATCH V6 13/27] cpr: preserve extra state

- Steve

On 8/6/2021 5:43 PM, Steve Sistare wrote:
> Provide the cpr-save, cpr-exec, and cpr-load commands for live update.
> These save and restore VM state, with minimal guest pause time, so that
> qemu may be updated to a new version in between.
> 
> cpr-save stops the VM and saves vmstate to an ordinary file.  It supports
> any type of guest image and block device, but the caller must not modify
> guest block devices between cpr-save and cpr-load.  It supports two modes:
> reboot and restart.
> 
> In reboot mode, the caller invokes cpr-save and then terminates qemu.
> The caller may then update the host kernel and system software and reboot.
> The caller resumes the guest by running qemu with the same arguments as the
> original process and invoking cpr-load.  To use this mode, guest ram must be
> mapped to a persistent shared memory file such as /dev/dax0.0, or /dev/shm
> PKRAM as proposed in https://lore.kernel.org/lkml/1617140178-8773-1-git-send-email-anthony.yznaga@oracle.com.
> 
> The reboot mode supports vfio devices if the caller first suspends the
> guest, such as 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.
> 
> Restart mode preserves the guest VM across a restart of the qemu process.
> After cpr-save, the caller passes qemu command-line arguments to cpr-exec,
> which directly exec's the new qemu binary.  The arguments must include -S
> so new qemu starts in a paused state and waits for the cpr-load command.
> The restart mode supports vfio devices by preserving the vfio container,
> group, device, and event descriptors across the qemu re-exec, and by
> updating DMA mapping virtual addresses using VFIO_DMA_UNMAP_FLAG_VADDR and
> VFIO_DMA_MAP_FLAG_VADDR as defined in https://lore.kernel.org/kvm/1611939252-7240-1-git-send-email-steven.sistare@oracle.com/
> and integrated in Linux kernel 5.12.
> 
> To use the restart mode, qemu must be started with the memfd-alloc option,
> which allocates guest ram using memfd_create.  The memfd's are saved to
> the environment and kept open across exec, after which they are found from
> the environment and re-mmap'd.  Hence guest ram is preserved in place,
> albeit with new virtual addresses in the qemu process.
> 
> The caller resumes the guest by invoking cpr-load, which loads state from
> the file. If the VM was running at cpr-save time, then VM execution resumes.
> If the VM was suspended at cpr-save time (reboot mode), then the caller must
> issue a system_wakeup command to resume.
> 
> The first patches add reboot mode:
>   - memory: qemu_check_ram_volatile
>   - migration: fix populate_vfio_info
>   - migration: qemu file wrappers
>   - migration: simplify savevm
>   - vl: start on wakeup request
>   - cpr: reboot mode
>   - cpr: reboot HMP interfaces
> 
> The next patches add restart mode:
>   - memory: flat section iterator
>   - oslib: qemu_clear_cloexec
>   - machine: memfd-alloc option
>   - qapi: list utility functions
>   - vl: helper to request re-exec
>   - cpr: preserve extra state
>   - cpr: restart mode
>   - cpr: restart HMP interfaces
>   - hostmem-memfd: cpr for memory-backend-memfd
> 
> The next patches add vfio support for restart mode:
>   - pci: export functions for cpr
>   - vfio-pci: refactor for cpr
>   - vfio-pci: cpr part 1 (fd and dma)
>   - vfio-pci: cpr part 2 (msi)
>   - vfio-pci: cpr part 3 (intx)
> 
> The next patches preserve various descriptor-based backend devices across
> cprexec:
>   - vhost: reset vhost devices for cpr
>   - chardev: cpr framework
>   - chardev: cpr for simple devices
>   - chardev: cpr for pty
>   - chardev: cpr for sockets
>   - cpr: only-cpr-capable option
> 
> Here is an example of updating qemu from v4.2.0 to v4.2.1 using
> restart mode.  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) cpr-save /tmp/qemu.sav restart           |
> (qemu) cpr-exec qemu-system-x86_64 -S ...       |
> QEMU 4.2.1 monitor - type 'help' ...            |
> (qemu) info status                              |
> VM status: paused (prelaunch)                   |
> (qemu) cpr-load /tmp/qemu.sav                   |
> (qemu) info status                              |
> VM status: running                              |
> 
> 
> Here is an example of updating the host kernel using reboot mode.
> 
> 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) cpr-save /tmp/qemu.sav restart           |
> (qemu) quit                                     |
>                                                 |
> # systemctl kexec                               |
> kexec_core: Starting new kernel                 |
> ...                                             |
>                                                 |
> # qemu-system-x86_64 -S mem-path=/dev/dax0.0 ...|
> QEMU 4.2.1 monitor - type 'help' ...            |
> (qemu) info status                              |
> VM status: paused (prelaunch)                   |
> (qemu) cpr-load /tmp/qemu.sav                   |
> (qemu) info status                              |
> VM status: running                              |
> 
> Changes from V1 to V2:
>   - revert vmstate infrastructure changes
>   - refactor cpr functions into new files
>   - delete MADV_DOEXEC and use memfd + VFIO_DMA_UNMAP_FLAG_SUSPEND to
>     preserve memory.
>   - add framework to filter chardev's that support cpr
>   - save and restore vfio eventfd's
>   - modify cprinfo QMP interface
>   - incorporate misc review feedback
>   - remove unrelated and unneeded patches
>   - refactor all patches into a shorter and easier to review series
> 
> Changes from V2 to V3:
>   - rebase to qemu 6.0.0
>   - use final definition of vfio ioctls (VFIO_DMA_UNMAP_FLAG_VADDR etc)
>   - change memfd-alloc to a machine option
>   - Use qio_channel_socket_new_fd instead of adding qio_channel_socket_new_fd
>   - close monitor socket during cpr
>   - fix a few unreported bugs
>   - support memory-backend-memfd
> 
> Changes from V3 to V4:
>   - split reboot mode into separate patches
>   - add cprexec command
>   - delete QEMU_START_FREEZE, argv_main, and /usr/bin/qemu-exec
>   - add more checks for vfio and cpr compatibility, and recover after errors
>   - save vfio pci config in vmstate
>   - rename {setenv,getenv}_event_fd to {save,load}_event_fd
>   - use qemu_strtol
>   - change 6.0 references to 6.1
>   - use strerror(), use EXIT_FAILURE, remove period from error messages
>   - distribute MAINTAINERS additions to each patch
> 
> Changes from V4 to V5:
>   - rebase to master
> 
> Changes from V5 to V6:
>   vfio:
>   - delete redundant bus_master_enable_region in vfio_pci_post_load
>   - delete unmap.size warning
>   - fix phys_config memory leak
>   - add INTX support
>   - add vfio_named_notifier_init() helper
>   Other:
>   - 6.1 -> 6.2
>   - rename file -> filename in qapi
>   - delete cprinfo.  qapi introspection serves the same purpose.
>   - rename cprsave, cprexec, cprload -> cpr-save, cpr-exec, cpr-load
>   - improve documentation in qapi/cpr.json
>   - rename qemu_ram_volatile -> qemu_ram_check_volatile, and use
>     qemu_ram_foreach_block
>   - rename handle -> opaque
>   - use ERRP_GUARD
>   - use g_autoptr and g_autofree, and glib allocation functions
>   - conform to error conventions for bool and int function return values
>     and function names.
>   - remove word "error" in error messages
>   - rename as_flat_walk and its callback, and add comments.
>   - rename qemu_clr_cloexec -> qemu_clear_cloexec
>   - rename close-on-cpr -> reopen-on-cpr
>   - add strList utility functions
>   - factor out start on wakeup request to a separate patch
>   - deleted unnecessary layer (cprsave etc) and squashed QMP patches
>   - conditionally compile for CONFIG_VFIO
> 
> Steve Sistare (24):
>   memory: qemu_check_ram_volatile
>   migration: fix populate_vfio_info
>   migration: qemu file wrappers
>   migration: simplify savevm
>   vl: start on wakeup request
>   cpr: reboot mode
>   memory: flat section iterator
>   oslib: qemu_clear_cloexec
>   machine: memfd-alloc option
>   qapi: list utility functions
>   vl: helper to request re-exec
>   cpr: preserve extra state
>   cpr: restart mode
>   cpr: restart HMP interfaces
>   hostmem-memfd: cpr for memory-backend-memfd
>   pci: export functions for cpr
>   vfio-pci: refactor for cpr
>   vfio-pci: cpr part 1 (fd and dma)
>   vfio-pci: cpr part 2 (msi)
>   vfio-pci: cpr part 3 (intx)
>   chardev: cpr framework
>   chardev: cpr for simple devices
>   chardev: cpr for pty
>   cpr: only-cpr-capable option
> 
> Mark Kanda, Steve Sistare (3):
>   cpr: reboot HMP interfaces
>   vhost: reset vhost devices for cpr
>   chardev: cpr for sockets
> 
>  MAINTAINERS                   |  12 ++
>  backends/hostmem-memfd.c      |  21 +--
>  chardev/char-mux.c            |   1 +
>  chardev/char-null.c           |   1 +
>  chardev/char-pty.c            |  14 +-
>  chardev/char-serial.c         |   1 +
>  chardev/char-socket.c         |  36 +++++
>  chardev/char-stdio.c          |   8 ++
>  chardev/char.c                |  43 +++++-
>  gdbstub.c                     |   1 +
>  hmp-commands.hx               |  50 +++++++
>  hw/core/machine.c             |  19 +++
>  hw/pci/msix.c                 |  20 ++-
>  hw/pci/pci.c                  |   7 +-
>  hw/vfio/common.c              |  79 +++++++++--
>  hw/vfio/cpr.c                 | 160 ++++++++++++++++++++++
>  hw/vfio/meson.build           |   1 +
>  hw/vfio/pci.c                 | 301 +++++++++++++++++++++++++++++++++++++++---
>  hw/vfio/trace-events          |   1 +
>  hw/virtio/vhost.c             |  11 ++
>  include/chardev/char.h        |   6 +
>  include/exec/memory.h         |  39 ++++++
>  include/hw/boards.h           |   1 +
>  include/hw/pci/msix.h         |   5 +
>  include/hw/pci/pci.h          |   2 +
>  include/hw/vfio/vfio-common.h |   8 ++
>  include/hw/virtio/vhost.h     |   1 +
>  include/migration/cpr.h       |  31 +++++
>  include/monitor/hmp.h         |   3 +
>  include/qapi/util.h           |  28 ++++
>  include/qemu/osdep.h          |   1 +
>  include/sysemu/runstate.h     |   2 +
>  include/sysemu/sysemu.h       |   1 +
>  linux-headers/linux/vfio.h    |   6 +
>  migration/cpr-state.c         | 215 ++++++++++++++++++++++++++++++
>  migration/cpr.c               | 176 ++++++++++++++++++++++++
>  migration/meson.build         |   2 +
>  migration/migration.c         |   5 +
>  migration/qemu-file-channel.c |  36 +++++
>  migration/qemu-file-channel.h |   6 +
>  migration/savevm.c            |  21 +--
>  migration/target.c            |  24 +++-
>  migration/trace-events        |   5 +
>  monitor/hmp-cmds.c            |  68 ++++++----
>  monitor/hmp.c                 |   3 +
>  monitor/qmp.c                 |   3 +
>  qapi/char.json                |   7 +-
>  qapi/cpr.json                 |  76 +++++++++++
>  qapi/meson.build              |   1 +
>  qapi/qapi-schema.json         |   1 +
>  qapi/qapi-util.c              |  37 ++++++
>  qemu-options.hx               |  40 +++++-
>  softmmu/globals.c             |   1 +
>  softmmu/memory.c              |  46 +++++++
>  softmmu/physmem.c             |  55 ++++++--
>  softmmu/runstate.c            |  38 +++++-
>  softmmu/vl.c                  |  18 ++-
>  stubs/cpr-state.c             |  15 +++
>  stubs/cpr.c                   |   3 +
>  stubs/meson.build             |   2 +
>  trace-events                  |   1 +
>  util/oslib-posix.c            |   9 ++
>  util/oslib-win32.c            |   4 +
>  util/qemu-config.c            |   4 +
>  64 files changed, 1732 insertions(+), 111 deletions(-)
>  create mode 100644 hw/vfio/cpr.c
>  create mode 100644 include/migration/cpr.h
>  create mode 100644 migration/cpr-state.c
>  create mode 100644 migration/cpr.c
>  create mode 100644 qapi/cpr.json
>  create mode 100644 stubs/cpr-state.c
>  create mode 100644 stubs/cpr.c
>