Re: [PATCH V3 00/22] Live Update

[Steven Sistare]

Hi Michael,
  Alex has reviewed the vfio-pci patches.  If you could give me a thumbs-up or 
a 
needs-work on "pci: export functions for cpr", I would appreciate it.  Thanks!

[PATCH V3 10/22] pci: export functions for cpr
https://lore.kernel.org/qemu-devel/1620390320-301716-11-git-send-email-steven.sistare@oracle.com

- Steve

On 5/19/2021 12:43 PM, Steven Sistare wrote:
> Hi Michael, Marcel,
>   I hope you have time to review the pci and vfio-pci related patches in this
> series.  They are an essential part of the live update functionality.  The
> first 2 patches are straightforward, just exposing functions for use in vfio.
> The last 2 patches are more substantial.
> 
>   - pci: export functions for cpr
>   - vfio-pci: refactor for cpr
>   - vfio-pci: cpr part 1
>   - vfio-pci: cpr part 2
> 
> - Steve
> 
> On 5/7/2021 8:24 AM, Steve Sistare wrote:
>> Provide the cprsave and cprload 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.
>>
>> cprsave stops the VM and saves vmstate to an ordinary file.  It supports two
>> modes: restart and reboot.  For restart, cprsave exec's the qemu binary (or
>> /usr/bin/qemu-exec if it exists) with the same argv.  qemu restarts in a
>> paused state and waits for the cprload command.
>>
>> 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 calling cprload, which loads state from the file.  If the VM
>> was running at cprsave time, then VM execution resumes.  cprsave supports
>> any type of guest image and block device, but the caller must not modify
>> guest block devices between cprsave and cprload.
>>
>> 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.
>>
>> For the reboot mode, cprsave saves state and exits qemu, and the caller is
>> allowed to 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 calling cprload.  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 suspends the guest
>> instead of stopping the VM, 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.
>>
>> The first patches add helper functions:
>>
>>   - as_flat_walk
>>   - qemu_ram_volatile
>>   - oslib: qemu_clr_cloexec
>>   - util: env var helpers
>>   - machine: memfd-alloc option
>>   - vl: add helper to request re-exec
>>
>> The next patches implement cprsave and cprload:
>>
>>   - cpr
>>   - cpr: QMP interfaces
>>   - cpr: HMP interfaces
>>
>> The next patches add vfio support for the restart mode:
>>
>>   - pci: export functions for cpr
>>   - vfio-pci: refactor for cpr
>>   - vfio-pci: cpr part 1
>>   - vfio-pci: cpr part 2
>>
>> The next patches preserve various descriptor-based backend devices across
>> a cprsave restart:
>>
>>   - vhost: reset vhost devices upon cprsave
>>   - hostmem-memfd: cpr support
>>   - chardev: cpr framework
>>   - chardev: cpr for simple devices
>>   - chardev: cpr for pty
>>   - chardev: cpr for sockets
>>   - cpr: only-cpr-capable option
>>   - cpr: maintainers
>>   - simplify savevm
>>
>> 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                           |
>>
>> 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 existing channel socket function instead of defining new ones
>>   - close monitor socket during cpr
>>   - support memory-backend-memfd
>>   - fix a few unreported bugs
>>
>> Steve Sistare (18):
>>   as_flat_walk
>>   qemu_ram_volatile
>>   oslib: qemu_clr_cloexec
>>   util: env var helpers
>>   machine: memfd-alloc option
>>   vl: add helper to request re-exec
>>   cpr
>>   pci: export functions for cpr
>>   vfio-pci: refactor for cpr
>>   vfio-pci: cpr part 1
>>   vfio-pci: cpr part 2
>>   hostmem-memfd: cpr support
>>   chardev: cpr framework
>>   chardev: cpr for simple devices
>>   chardev: cpr for pty
>>   cpr: only-cpr-capable option
>>   cpr: maintainers
>>   simplify savevm
>>
>> Mark Kanda, Steve Sistare (4):
>>   cpr: QMP interfaces
>>   cpr: HMP interfaces
>>   vhost: reset vhost devices upon cprsave
>>   chardev: cpr for sockets
>>
>>  MAINTAINERS                   |  11 +++
>>  backends/hostmem-memfd.c      |  21 +++--
>>  chardev/char-mux.c            |   1 +
>>  chardev/char-null.c           |   1 +
>>  chardev/char-pty.c            |  15 ++-
>>  chardev/char-serial.c         |   1 +
>>  chardev/char-socket.c         |  35 +++++++
>>  chardev/char-stdio.c          |   8 ++
>>  chardev/char.c                |  41 +++++++-
>>  gdbstub.c                     |   1 +
>>  hmp-commands.hx               |  44 +++++++++
>>  hw/core/machine.c             |  19 ++++
>>  hw/pci/msi.c                  |   4 +
>>  hw/pci/msix.c                 |  20 ++--
>>  hw/pci/pci.c                  |   7 +-
>>  hw/vfio/common.c              |  68 +++++++++++++-
>>  hw/vfio/cpr.c                 | 131 ++++++++++++++++++++++++++
>>  hw/vfio/meson.build           |   1 +
>>  hw/vfio/pci.c                 | 214 
>> ++++++++++++++++++++++++++++++++++++++----
>>  hw/vfio/trace-events          |   1 +
>>  hw/virtio/vhost.c             |  11 +++
>>  include/chardev/char.h        |   6 ++
>>  include/exec/memory.h         |  25 +++++
>>  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       |  17 ++++
>>  include/monitor/hmp.h         |   3 +
>>  include/qemu/env.h            |  23 +++++
>>  include/qemu/osdep.h          |   1 +
>>  include/sysemu/runstate.h     |   2 +
>>  include/sysemu/sysemu.h       |   2 +
>>  linux-headers/linux/vfio.h    |  27 ++++++
>>  migration/cpr.c               | 200 +++++++++++++++++++++++++++++++++++++++
>>  migration/meson.build         |   1 +
>>  migration/migration.c         |   5 +
>>  migration/savevm.c            |  21 ++---
>>  migration/savevm.h            |   2 +
>>  monitor/hmp-cmds.c            |  48 ++++++++++
>>  monitor/hmp.c                 |   3 +
>>  monitor/qmp-cmds.c            |  31 ++++++
>>  monitor/qmp.c                 |   3 +
>>  qapi/char.json                |   5 +-
>>  qapi/cpr.json                 |  76 +++++++++++++++
>>  qapi/meson.build              |   1 +
>>  qapi/qapi-schema.json         |   1 +
>>  qemu-options.hx               |  39 +++++++-
>>  softmmu/globals.c             |   2 +
>>  softmmu/memory.c              |  48 ++++++++++
>>  softmmu/physmem.c             |  49 ++++++++--
>>  softmmu/runstate.c            |  49 +++++++++-
>>  softmmu/vl.c                  |  21 ++++-
>>  stubs/cpr.c                   |   3 +
>>  stubs/meson.build             |   1 +
>>  trace-events                  |   1 +
>>  util/env.c                    |  99 +++++++++++++++++++
>>  util/meson.build              |   1 +
>>  util/oslib-posix.c            |   9 ++
>>  util/oslib-win32.c            |   4 +
>>  util/qemu-config.c            |   4 +
>>  62 files changed, 1431 insertions(+), 74 deletions(-)
>>  create mode 100644 hw/vfio/cpr.c
>>  create mode 100644 include/migration/cpr.h
>>  create mode 100644 include/qemu/env.h
>>  create mode 100644 migration/cpr.c
>>  create mode 100644 qapi/cpr.json
>>  create mode 100644 stubs/cpr.c
>>  create mode 100644 util/env.c
>>