Re: [Qemu-devel] [RFC 00/29] postcopy+vhost-user/shared ram

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Dr. David Alan Gilbert (git) (dgilbert@redhat.com) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Hi,
>   This is a RFC/WIP series that enables postcopy migration
> with shared memory to a vhost-user process.
> It's based off current-head + Juan's load_cleanup series, and
> Alexey's bitmap series (v4).  It's very lightly tested and seems
> to work, but it's quite rough.

Marc-André asked if I had a git with it all applied; so here we are:
https://github.com/dagrh/qemu/commits/vhost
git@github.com:dagrh/qemu.git on the vhost branch

Dave

> I've modified the vhost-user-bridge (aka vhub) in qemu's tests/ to
> use the new feature, since this is about the simplest
> client around.
> 
> Structure:
> 
> The basic idea is that near the start of postcopy, the client
> opens its own userfaultfd fd and sends that back to QEMU over
> the socket it's already using for VHUST_USER_* commands.
> Then when VHOST_USER_SET_MEM_TABLE arrives it registers the
> areas with userfaultfd and sends the mapped addresses back to QEMU.
> 
> QEMU then reads the clients UFD in it's fault thread and issues
> requests back to the source as needed.
> QEMU also issues 'WAKE' ioctls on the UFD to let the client know
> that the page has arrived and can carry on.
> 
> A new feature (VHOST_USER_PROTOCOL_F_POSTCOPY) is added so that
> the QEMU knows the client can talk postcopy.
> Three new messages (VHOST_USER_POSTCOPY_{ADVISE/LISTEN/END}) are
> added to guide the process along.
> 
> Current known issues:
>    I've not tested it with hugepages yet; and I suspect the madvises
>    will need tweaking for it.
> 
>    The qemu gets to see the base addresses that the client has its
>    regions mapped at; that's not great for security
> 
>    Take care of deadlocking; any thread in the client that
>    accesses a userfault protected page can stall.
> 
>    There's a nasty hack of a lock around the set_mem_table message.
> 
>    I've not looked at the recent IOMMU code.
> 
>    Some cleanup and a lot of corner cases need thinking about.
> 
>    There are probably plenty of unknown issues as well.
> 
> Test setup:
>   I'm running on one host at the moment, with the guest
>   scping a large file from the host as it migrates.
>   The setup is based on one I found in the vhost-user setups.
>   You'll need a recent kernel for the shared memory support
>   in userfaultfd, and userfault isn't that happy if a process
>   using shared memory core's - so make sure you have the
>   latest fixes.
> 
> SESS=vhost
> ulimit -c unlimited
> tmux -L $SESS new-session -d
> tmux -L $SESS set-option -g history-limit 30000
> # Start a router using the system qemu
> tmux -L $SESS new-window -n router ./x86_64-softmmu/qemu-system-x86_64 -M none -nographic -net socket,vlan=0,udp=loca
> lhost:4444,localaddr=localhost:5555 -net socket,vlan=0,udp=localhost:4445,localaddr=localhost:5556 -net user,vlan=0
> tmux -L $SESS set-option -g set-remain-on-exit on
> # Start source vhost bridge
> tmux -L $SESS new-window -n srcvhostbr "./tests/vhost-user-bridge -u /tmp/vubrsrc.sock 2>src-vub-log"
> sleep 0.5
> tmux -L $SESS new-window -n source "./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 8G -smp 2 -object memory-backe
> nd-file,id=mem,size=8G,mem-path=/dev/shm,share=on -numa node,memdev=mem -mem-prealloc -chardev socket,id=char0,path=/
> tmp/vubrsrc.sock -netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce -device virtio-net-pci,netdev=mynet1 my.qcow2 -net none -vnc :0 -monitor stdio -trace events=/root/trace-file 2>src-qemu-log "
> # Start dest vhost bridge
> tmux -L $SESS new-window -n destvhostbr "./tests/vhost-user-bridge -u /tmp/vubrdst.sock -l 127.0.0.1:4445 -r 127.0.0.
> 1:5556 2>dst-vub-log"
> sleep 0.5
> tmux -L $SESS new-window -n dest "./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 8G -smp 2 -object memory-backend
> -file,id=mem,size=8G,mem-path=/dev/shm,share=on -numa node,memdev=mem -mem-prealloc -chardev socket,id=char0,path=/tm
> p/vubrdst.sock -netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce -device virtio-net-pci,netdev=mynet1 my.qcow2 -net none -vnc :1 -monitor stdio -incoming tcp::8888 -trace events=/root/trace-file 2>dst-qemu-log"
> tmux -L $SESS send-keys -t source "migrate_set_capability postcopy-ram on
> tmux -L $SESS send-keys -t source "migrate_set_speed 20M
> tmux -L $SESS send-keys -t dest "migrate_set_capability postcopy-ram on
> 
> then once booted:
> tmux -L vhost send-keys -t source 'migrate -d tcp:0:8888^M'
> tmux -L vhost send-keys -t source 'migrate_start_postcopy^M'
> (Note those ^M's are actual ctrl-M's i.e. ctrl-v ctrl-M)
> 
> 
> Dave
> 
> Dr. David Alan Gilbert (29):
>   RAMBlock/migration: Add migration flags
>   migrate: Update ram_block_discard_range for shared
>   qemu_ram_block_host_offset
>   migration/ram: ramblock_recv_bitmap_test_byte_offset
>   postcopy: use UFFDIO_ZEROPAGE only when available
>   postcopy: Add notifier chain
>   postcopy: Add vhost-user flag for postcopy and check it
>   vhost-user: Add 'VHOST_USER_POSTCOPY_ADVISE' message
>   vhub: Support sending fds back to qemu
>   vhub: Open userfaultfd
>   postcopy: Allow registering of fd handler
>   vhost+postcopy: Register shared ufd with postcopy
>   vhost+postcopy: Transmit 'listen' to client
>   vhost+postcopy: Register new regions with the ufd
>   vhost+postcopy: Send address back to qemu
>   vhost+postcopy: Stash RAMBlock and offset
>   vhost+postcopy: Send requests to source for shared pages
>   vhost+postcopy: Resolve client address
>   postcopy: wake shared
>   postcopy: postcopy_notify_shared_wake
>   vhost+postcopy: Add vhost waker
>   vhost+postcopy: Call wakeups
>   vub+postcopy: madvises
>   vhost+postcopy: Lock around set_mem_table
>   vhu: enable = false on get_vring_base
>   vhost: Add VHOST_USER_POSTCOPY_END message
>   vhost+postcopy: Wire up POSTCOPY_END notify
>   postcopy: Allow shared memory
>   vhost-user: Claim support for postcopy
> 
>  contrib/libvhost-user/libvhost-user.c | 178 ++++++++++++++++-
>  contrib/libvhost-user/libvhost-user.h |   8 +
>  exec.c                                |  44 +++--
>  hw/virtio/trace-events                |  13 ++
>  hw/virtio/vhost-user.c                | 293 +++++++++++++++++++++++++++-
>  include/exec/cpu-common.h             |   3 +
>  include/exec/ram_addr.h               |   2 +
>  migration/migration.c                 |   3 +
>  migration/migration.h                 |   8 +
>  migration/postcopy-ram.c              | 357 +++++++++++++++++++++++++++-------
>  migration/postcopy-ram.h              |  69 +++++++
>  migration/ram.c                       |   5 +
>  migration/ram.h                       |   1 +
>  migration/savevm.c                    |  13 ++
>  migration/trace-events                |   6 +
>  trace-events                          |   3 +
>  vl.c                                  |   4 +-
>  17 files changed, 926 insertions(+), 84 deletions(-)
> 
> -- 
> 2.13.0
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK