Re: [PATCH 1/1] KVM: selftests: add kvmclock drift test

[David Woodhouse]

On Sat, 2024-01-06 at 00:33 -0800, Dongli Zhang wrote:
> There is kvmclock drift issue during the vCPU hotplug. It has been fixed by
> the commit c52ffadc65e2 ("KVM: x86: Don't unnecessarily force masterclock
> update on vCPU hotplug").
> 
> This is to add the test to verify if the master clock is updated when we
> write 0 to MSR_IA32_TSC from the host side.
> 
> Here is the usage example on the KVM with the bugfix reverted.
> 
> $ ./kvm_clock_drift -v -p 5
> kvmclock based on old pvclock_vcpu_time_info: 5012221999
>   version:           2
>   tsc_timestamp:     3277968
>   system_time:       11849519
>   tsc_to_system_mul: 2152530255
>   tsc_shift:         0
>   flags:             1
> 
> kvmclock based on new pvclock_vcpu_time_info: 5012222411
>   version:           4
>   tsc_timestamp:     9980576184
>   system_time:       5012222411
>   tsc_to_system_mul: 2152530255
>   tsc_shift:         0
>   flags:             1
> 
> ==== Test Assertion Failure ====
>   x86_64/kvm_clock_drift.c:216: clock_old == clock_new
>   pid=14257 tid=14257 errno=4 -  Interrupted system call
>      1  0x000000000040277b: main at kvm_clock_drift.c:216
>      2  0x00007f7766fa7e44: ?? ??:0
>      3  0x000000000040286d: _start at ??:?
>   kvmclock drift detected, old=5012221999, new=5012222411
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>

We should extend this to cover live update — it should create a
*second* KVM, migrate the guest including its clock information to
that, and validate that the kvmclock information still doesn't change.

Ideally during a leap second.

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