VM crashed while hot-plugging memory

[Yangming]

Hello all:

 

I found VM crashed while hot-plugging memory.

 

Base infomation:

qemu version: qemu-master

requirements: hugepages, virtio-gpu

 

It happens by the following steps:

1. Booting a VM with hugepages and a virtio-gpu device.

2. Connecting VNC of the VM.

3. After the VM booted, hot-plugging 512G memory.

4. Then you can find that the image in vnc is blocked and the worse thing is that the VM crashed.

 

Actually the vcpu is blocked because of dead lock.

 

Analysis:

As when hot-pluging the BQL is held, at the meanwhile, virtio-gpu is trying to hold the BQL for writing date. Then a vcpu is blocked waiting for hugepages hot-plugging, specifically, waiting for touching pages. If the blocked vcpu stops for several seconds, the soft lockup will happen, if it stops for a long time, e.g. 30s, the VM will crash.

 

I am wandering if there are some ideas to avoid VM soft lockup and even VM crash ?

 

Thank you!

kind regards!