RE: [PATCH v19 for-4.14 00/13] VM forking

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Tamas K 
> Lengyel
> Sent: 01 June 2020 14:22
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>; Stefano Stabellini 
> <sstabellini@xxxxxxxxxx>; Tamas K Lengyel
> <tamas.lengyel@xxxxxxxxx>; Jun Nakajima <jun.nakajima@xxxxxxxxx>; Wei Liu 
> <wl@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; Ian Jackson <ian.jackson@xxxxxxxxxxxxx>; George 
> Dunlap
> <george.dunlap@xxxxxxxxxx>; Tamas K Lengyel <tamas@xxxxxxxxxxxxx>; Jan 
> Beulich <jbeulich@xxxxxxxx>;
> Anthony PERARD <anthony.perard@xxxxxxxxxx>; Julien Grall <julien@xxxxxxx>; 
> Roger Pau Monné
> <roger.pau@xxxxxxxxxx>
> Subject: [PATCH v19 for-4.14 00/13] VM forking

Hi,

  This series looks to be largely un-acked so, since we are now past the freeze 
date, I don't really think it can go into 4.14. Is there a particular reason 
that you think it should be considered?

  Paul

> 
> The following patches are part of the series that implement VM forking for
> Intel HVM guests to allow for the fast creation of identical VMs without the
> assosciated high startup costs of booting or restoring the VM from a savefile.
> 
> JIRA issue: https://xenproject.atlassian.net/browse/XEN-89
> 
> The fork operation is implemented as part of the "xl fork-vm" command:
>     xl fork-vm -C <config> -Q <qemu-save-file> <parent_domid>
> 
> By default a fully functional fork is created. The user is in charge however 
> to
> create the appropriate config file for the fork and to generate the QEMU save
> file before the fork-vm call is made. The config file needs to give the
> fork a new name at minimum but other settings may also require changes. 
> Certain
> settings in the config file of both the parent and the fork have to be set to
> default. Details are documented.
> 
> The interface also allows to split the forking into two steps:
>     xl fork-vm --launch-dm no \
>                -m <max-vcpus> \
>                          -p <parent_domid>
>       xl fork-vm --launch-dm late \
>                  -C <config_file_for_fork> \
>                          -Q <qemu_save_file> \
>                          <fork_domid>
> 
> The split creation model is useful when the VM needs to be created as fast as
> possible. The forked VM can be unpaused without the device model being 
> launched
> to be monitored and accessed via VMI. Note however that without its device
> model running (depending on what is executing in the VM) it is bound to
> misbehave or even crash when its trying to access devices that would be
> emulated by QEMU. We anticipate that for certain use-cases this would be an
> acceptable situation, in case for example when fuzzing is performed of code
> segments that don't access such devices.
> 
> Launching the device model requires the QEMU Xen savefile to be generated
> manually from the parent VM. This can be accomplished simply by connecting to
> its QMP socket and issuing the "xen-save-devices-state" command. For example
> using the standard tool socat these commands can be used to generate the file:
>     socat - UNIX-CONNECT:/var/run/xen/qmp-libxl-<parent_domid>
>       { "execute": "qmp_capabilities" }
>       { "execute": "xen-save-devices-state", \
>               "arguments": { "filename": "/path/to/save/qemu_state", \
>                                               "live": false} }
> 
> The series has been tested with Windows VMs and functions as expected. Linux
> VMs when forked from a running VM will have a frozen VNC screen. Linux VMs at
> this time can only be forked with a working device model when the parent VM 
> was
> restored from a snapshot using "xl restore -p". This is a known limitation due
> to Linux VMs having to be made aware of being saved/migrated.
> 
> New in v19:
>       Including all the patches currently outstanding into the series
>       Breaking up libxl/xl patch to many sub-patches to make it easier to 
> review
>       libxl/xl is now reduced to the bare essential to launch QEMU for a VM 
> fork
> 
> Tamas K Lengyel (13):
>   x86/mem_sharing: block interrupt injection for forks
>   tools/libxc: xc_memshr_fork with interrupts blocked
>   tools/libxl: Split libxl__domain_make
>   tools/libxl: populate xenstore entries when launching dm for VM fork
>   tools/libxl: Add checks for dm_restore_file
>   tools/libxl: adjust domcreate_bootloader_done
>   tools/libxl: Adjust libxl__build_pre
>   tools/libxl: Adjust libxl__build_post
>   tools/libxl: libxl__build_hvm_fork
>   tools/libxl: set QEMU saved_state from dm_restore_file
>   tools/libxl: Add VM forking public functions
>   tools/xl: Add xl fork-vm command
>   tools/xl: document fork-vm command
> 
>  docs/man/xl.1.pod.in             |  39 +++++++++
>  tools/libxc/include/xenctrl.h    |   3 +-
>  tools/libxc/xc_memshr.c          |   4 +-
>  tools/libxl/libxl.h              |  10 +++
>  tools/libxl/libxl_create.c       | 134 +++++++++++++++++++++++++------
>  tools/libxl/libxl_dm.c           |   2 +-
>  tools/libxl/libxl_dom.c          |  59 +++++++++++---
>  tools/libxl/libxl_internal.h     |   5 +-
>  tools/libxl/libxl_types.idl      |   1 +
>  tools/xl/Makefile                |   2 +-
>  tools/xl/xl.h                    |   4 +
>  tools/xl/xl_cmdtable.c           |  13 +++
>  tools/xl/xl_forkvm.c             | 122 ++++++++++++++++++++++++++++
>  tools/xl/xl_vmcontrol.c          |  13 +++
>  xen/arch/x86/hvm/vmx/intr.c      |   6 ++
>  xen/arch/x86/mm/mem_sharing.c    |   6 +-
>  xen/include/asm-x86/hvm/domain.h |   2 +-
>  xen/include/public/memory.h      |   3 +
>  18 files changed, 383 insertions(+), 45 deletions(-)
>  create mode 100644 tools/xl/xl_forkvm.c
> 
> --
> 2.25.1
>