Re: [Xen-devel] [PATCH v3] x86/hvm: fix saved pmtimer value

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.09.15 at 03:18, <kouya@xxxxxxxxxxxxxx> wrote:
> Jan Beulich <JBeulich@xxxxxxxx> writes:
>> From: Kouya Shimura <kouya@xxxxxxxxxxxxxx>
>>
>> The ACPI PM timer is sometimes broken on live migration.
>> Since vcpu->arch.hvm_vcpu.guest_time is always zero in other than
>> "delay for missed ticks mode". Even in "delay for missed ticks mode",
>> vcpu's guest_time field is not valid (i.e. zero) when
>> the state of vcpu is "blocked". (see pt_save_timer function)
>>
>> The original author (Tim Deegan) of pmtimer_save() must have intended
>> that it saves the last scheduled time of the vcpu. Unfortunately it was
>> already implied this bug. FYI, there is no other timer mode than 
>> "delay for missed ticks mode" then.
>>
>> For consistency with HPET, pmtimer_save() should refer hvm_get_guest_time()
>> to update the counter as well as hpet_save() does. 
>>
>> Without this patch, the clock of windows server 2012R2 without HPET
>> might leap forward several minutes on live migration.
>>
>> Signed-off-by: Kouya Shimura <kouya@xxxxxxxxxxxxxx>
>>
>> Retain use of ->arch.hvm_vcpu.guest_time when non-zero. Do the inverse
>> adjustment for vHPET.
> 
> I'm fine with this change.
> Why not modify the subject too?

Right - adding "and hpet" to it.

Jan


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