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

[Tim Deegan <tim@xxxxxxx>]

At 08:44 -0600 on 10 Sep (1441874674), Jan Beulich wrote:
> 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.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Reviewed-by: Tim Deegan <tim@xxxxxxx>

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