Re: [PATCH] i386: Fix KVM_CAP_ADJUST_CLOCK capability check

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Vitaly Kuznetsov <vkuznets@redhat.com> writes:

> Vitaly Kuznetsov <vkuznets@redhat.com> writes:
>
>> KVM commit c68dc1b577ea ("KVM: x86: Report host tsc and realtime values in
>> KVM_GET_CLOCK") broke migration of certain workloads, e.g. Win11 + WSL2
>> guest reboots immediately after migration. KVM, however, is not to
>> blame this time. When KVM_CAP_ADJUST_CLOCK capability is checked, the
>> result is all supported flags (which the above mentioned KVM commit
>> enhanced) but kvm_has_adjust_clock_stable() wants it to be
>> KVM_CLOCK_TSC_STABLE precisely. The result is that 'clock_is_reliable'
>> is not set in vmstate and the saved clock reading is discarded in
>> kvmclock_vm_state_change().
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  target/i386/kvm/kvm.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
>> index a1fd1f53791d..c33192a87dcb 100644
>> --- a/target/i386/kvm/kvm.c
>> +++ b/target/i386/kvm/kvm.c
>> @@ -157,7 +157,7 @@ bool kvm_has_adjust_clock_stable(void)
>>  {
>>      int ret = kvm_check_extension(kvm_state, KVM_CAP_ADJUST_CLOCK);
>>  
>> -    return (ret == KVM_CLOCK_TSC_STABLE);
>> +    return ret & KVM_CLOCK_TSC_STABLE;
>>  }
>>  
>>  bool kvm_has_adjust_clock(void)
>
> Ping) This issue seems to introduce major migration issues with KVM >= v5.16

Ping)

-- 
Vitaly