Re: migrate from qemu 2.11 to qemu 4.2 failed on arm machine

[Peter Maydell]

On Mon, 30 Jan 2023 at 06:53, Jiatong Shen <yshxxsjt715@gmail.com> wrote:
>
> Hello community experts,
>
>    I am facing an issue to migrate a virtual machine from qemu 2.11 to qemu 
> 4.2 node. The command using on src node is
>
> qemu-system-aarch64 -M virt -vnc :2 -rtc base=utc,driftfix=slew -smp 2 -m 
> 4096 -cpu host -enable-kvm -nodefaults -incoming :4443
>
> on the dst node, the command is
>
> qemu-system-aarch64 -M virt-2.11 -enable-kvm -cpu host -smp 2 -m 4096 
> -incoming tcp::4443 -rtc base=utc,driftfix=slew -nodefaults
>
> after running migrate tcp:localhost:4443, the dest machine failed with 
> following message
>
> Segmentation fault (core dumped)
>
> I try to debug and find the following trace: 0x0000aaab0f07262c in 
> armv7m_nvic_neg_prio_requested (opaque=0x0, secure=false) at 
> /root/qemu-4.2.1/hw/intc/armv7m_nvic.c:391.
>
> After some investigation, I believe the issue is from 
> https://elixir.bootlin.com/qemu/v4.2.1/source/target/arm/helper.c#L11134 and 
> ARM_FEATURE_M 's value is changed from 2.11 to 4.2.
>
> My question is do we support migrating from 2.11 to 4.2  on aarch64 platform? 
> Thank you much for the help

I think in theory it was supposed to work. In practice,
both of those releases are very very old, and if it
doesn't work then it doesn't work. This particular
migration bug was fixed in commit af903caed9fc62cc
in 2021 (there is no need to migrate the 'features'
field at all). If you really need to run 4.2.1 then
the patch should be easy to backport, but I would
suggest running a newer QEMU anyway.

thanks
-- PMM