Re: [PATCH] target/i386: Reset TSCs of parked vCPUs too on VM reset

[Michael Tokarev]

12.12.2024 17:51, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>
> Since commit 5286c3662294 ("target/i386: properly reset TSC on reset")
> QEMU writes the special value of "1" to each online vCPU TSC on VM reset
> to reset it.
>
> However parked vCPUs don't get that handling and due to that their TSCs
> get desynchronized when the VM gets reset.
> This in turn causes KVM to turn off PVCLOCK_TSC_STABLE_BIT in its exported
> PV clock.
> Note that KVM has no understanding of vCPU being currently parked.
>
> Without PVCLOCK_TSC_STABLE_BIT the sched clock is marked unstable in
> the guest's kvm_sched_clock_init().
> This causes a performance regressions to show in some tests.
>
> Fix this issue by writing the special value of "1" also to TSCs of parked
> vCPUs on VM reset.
...

This looks like it should be picked up for stable too, what do you think?

Thanks,

/mjt