hypervisor: kvm: Save KVM HyperV SynIC emulation state - #7492

Just FYI, I am not sure if this is really related:

I just tested snapshot/restore with my WindowsPE installer setup. When restoring the snapshot, I am no longer able to connect to the windows VM via network. I only see the following:

./cloud-hypervisor --api-socket=/tmp/chv.sock --restore source_url=file:///tmp/windows
cloud-hypervisor:   0.423612s: <vmm> WARN:vmm/src/config.rs:2526 -- Using TTY output for multiple consoles: ["virtio-console", "serial-console"]
cloud-hypervisor:   0.424963s: <vmm> WARN:net_util/src/open_tap.rs:88 -- Tap tap0 already exists. IP configuration will not be overwritten.

Just FYI, I am not sure if this is really related:

I just tested snapshot/restore with my WindowsPE installer setup. When restoring the snapshot, I am no longer able to connect to the windows VM via network. I only see the following:

./cloud-hypervisor --api-socket=/tmp/chv.sock --restore source_url=file:///tmp/windows
cloud-hypervisor:   0.423612s: <vmm> WARN:vmm/src/config.rs:2526 -- Using TTY output for multiple consoles: ["virtio-console", "serial-console"]
cloud-hypervisor:   0.424963s: <vmm> WARN:net_util/src/open_tap.rs:88 -- Tap tap0 already exists. IP configuration will not be overwritten.

Are you saying that somehow not restoring the state makes this work? Did you have hyperv_synic enabled before?

Are you saying that somehow not restoring the state makes this work? Did you have hyperv_synic enabled before?

I never tested snapshot/restore with Windows before I saw this PR. I just have a WindowsPE installer setup here which works great when I boot it normally, but I am unable to do a snapshot/restore cycle with this image. Once restored, the ip of the guest is no longer reachable. SynIC was enabled when I bootet the VM initially.

Are you saying that somehow not restoring the state makes this work? Did you have hyperv_synic enabled before?

I never tested snapshot/restore with Windows before I saw this PR. I just have a WindowsPE installer setup here which works great when I boot it normally, but I am unable to do a snapshot/restore cycle with this image. Once restored, the ip of the guest is no longer reachable. SynIC was enabled when I bootet the VM initially.

Okay, then we cannot say for sure if this issue is caused by this change or not.

Just FYI, I am not sure if this is really related:

I just tested snapshot/restore with my WindowsPE installer setup. When restoring the snapshot, I am no longer able to connect to the windows VM via network. I only see the following:

./cloud-hypervisor --api-socket=/tmp/chv.sock --restore source_url=file:///tmp/windows
cloud-hypervisor:   0.423612s: <vmm> WARN:vmm/src/config.rs:2526 -- Using TTY output for multiple consoles: ["virtio-console", "serial-console"]
cloud-hypervisor:   0.424963s: <vmm> WARN:net_util/src/open_tap.rs:88 -- Tap tap0 already exists. IP configuration will not be overwritten.

@tpressure
It looks like there's a potential conflict with the tap configuration during restore. This is my startup command, and I found that the network works normally after restore.

OS: Windows 11 IoT Enterprise LTSC 2024

#!/bin/bash

FW=CLOUDHV.fd
DISK0=disk0-os.raw

rm -f api.sock
sudo cloud-hypervisor \
	--api-socket api.sock \
	--kernel $FW \
	--disk path=$DISK0 \
	--cpus boot=4,kvm_hyperv=on \
	--memory size=8G \
	--serial tty \
	--console off \
	--seccomp false \
	--net tap=,ip=192.168.249.1,mask=255.255.255.0

#!/bin/bash

snapshot=$(pwd)/snapshot_$(date +"%Y%m%d_%H%M%S")
echo "$snapshot" > latest_snapshot

mkdir -p "$snapshot"

sudo ch-remote --api-socket ./api.sock pause
sudo ch-remote --api-socket ./api.sock snapshot file://$snapshot
sudo ch-remote --api-socket ./api.sock shutdown-vmm

#!/bin/bash

rm -f api.sock
sudo cloud-hypervisor --api-socket ./api.sock --seccomp false

#!/bin/bash

snapshot=$(cat latest_snapshot)

sudo ch-remote --api-socket ./api.sock restore source_url=file://$snapshot
sudo ch-remote --api-socket ./api.sock resume

It looks like there's a potential conflict with the tap configuration during restore. This is my startup command, and I found that the network works normally after restore.

OS: Windows 11 IoT Enterprise LTSC 2024

Thanks for the pointers. I will give this a spin later this week.