live migration failure with kvm_put_msr_feature_control: Assertion `ret == 1' failed

[Jiatong Shen]

Hello community,

   I am trying to understand an error message produced during live migration. The error message are produced when trying to do a live migration from a host which enabled nested kvm_intel to a host where nest virtualization has been disabled. The full error message is

/build/qemu-vx6Pwx/qemu-2.11+dfsg/target/i386/kvm.c:1596: kvm_put_msr_feature_control: Assertion `ret == 1' failed.

guest vm has -cpu host and -enable-kvm

After some googling, looks like the assertion failed here https://github.com/qemu/qemu/blob/c99e34e537f13a431a80e3e414e5904e9dd0a116/target/i386/kvm/kvm.c#L2649 but I had a hard time understanding the background...

so in all my question is 

1. What  is the difference between vmxon and guest mode?

2. What is  MSR_IA32_FEATURE_CONTROL ?

3. I am using qemu 2.11 but live migration succeeds on ubuntu 16.04 with kernel 4.4..

so does this assert also has something to do with kernel?

Thank you.

--

Best Regards,

Jiatong Shen