Re: KVM: x86: disable master clock if TSC is reset during suspend (v3)

Paolo Bonzini
2014-05-21T10:01:32Z

Il 21/05/2014 10:26, Alexander Graf ha scritto:
>
> On 14.05.14 18:00, Paolo Bonzini wrote:
>> Il 14/05/2014 17:43, Marcelo Tosatti ha scritto:
>>>
>>> Updating system_time from the kernel clock once master clock
>>> has been enabled can result in time backwards event, in case
>>> kernel clock frequency is lower than TSC frequency.
>>>
>>> Disable master clock in case its necessary to update it
>>> from the resume path.
>>>
>>> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>>>
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index de0931c..c098728 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -106,6 +106,8 @@ EXPORT_SYMBOL_GPL(kvm_max_guest_tsc_khz);
>>> static u32 tsc_tolerance_ppm = 250;
>>> module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
>>>
>>> +static bool backwards_tsc_observed = false;
>>> +
>>> #define KVM_NR_SHARED_MSRS 16
>>>
>>> struct kvm_shared_msrs_global {
>>> @@ -1471,7 +1473,8 @@ static void pvclock_update_vm_gtod_copy(struct
>>> kvm *kvm)
>>> &ka->master_kernel_ns,
>>> &ka->master_cycle_now);
>>>
>>> - ka->use_master_clock = host_tsc_clocksource & vcpus_matched;
>>> + ka->use_master_clock = host_tsc_clocksource && vcpus_matched
>>> + && !backwards_tsc_observed;
>>>
>>> if (ka->use_master_clock)
>>> atomic_set(&kvm_guest_has_master_clock, 1);
>>> @@ -6939,6 +6942,7 @@ int kvm_arch_hardware_enable(void *garbage)
>>> */
>>> if (backwards_tsc) {
>>> u64 delta_cyc = max_tsc - local_tsc;
>>> + backwards_tsc_observed = true;
>>> list_for_each_entry(kvm, &vm_list, vm_list) {
>>> kvm_for_each_vcpu(i, vcpu, kvm) {
>>> vcpu->arch.tsc_offset_adjustment += delta_cyc;
>>>
>>
>> Applying to kvm/master, thanks.
>
> Thanks. Can you please make sure to CC qemu-stable when sending a pull
> request?

Now I will.

Paolo :)