Re: [PATCH v3] x86/vtsc: update vcpu_time in hvm_set_guest_time

[Diana Crisan <dcrisan@flexiant.com>]

On 05/06/13 14:06, George Dunlap wrote:
> On 05/06/13 13:02, Diana Crisan wrote:
>> On 04/06/13 16:32, Roger Pau Monne wrote:
>>> When using a vtsc, hvm_set_guest_time changes hvm_vcpu.stime_offset,
>>> which is used in the vcpu time structure to calculate the
>>> tsc_timestamp, so after updating stime_offset we need to propagate the
>>> change to vcpu_time in order for the guest to get the right time if
>>> using the PV clock.
>>>
>>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>>> Cc: Keir Fraser <keir@xen.org>
>>> Cc: Jan Beulich <jbeulich@suse.com>
>>> Cc: George Dunlap <george.dunlap@eu.citrix.com>
>> Tested-By: Diana Crisan  <dcrisan@flexiant.com>
>>> ---
>>> Changes since v2:
>>>   * Check for v == current instead of v->is_running to know if the vcpu
>>>     is running.
>>> Changes since v1:
>>>   * Perform the call to update_vcpu_system_time in hvm_set_guest_time
>>>     if the offset has changed and the vCPU is running.
>>> ---
>>>   xen/arch/x86/hvm/vpt.c |   13 ++++++++++++-
>>>   1 files changed, 12 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/xen/arch/x86/hvm/vpt.c b/xen/arch/x86/hvm/vpt.c
>>> index 8dee662..4b1e1a3 100644
>>> --- a/xen/arch/x86/hvm/vpt.c
>>> +++ b/xen/arch/x86/hvm/vpt.c
>>> @@ -57,7 +57,18 @@ u64 hvm_get_guest_time(struct vcpu *v)
>>>     void hvm_set_guest_time(struct vcpu *v, u64 guest_time)
>>>   {
>>> -    v->arch.hvm_vcpu.stime_offset += guest_time - 
>>> hvm_get_guest_time(v);
>>> +    u64 offset = guest_time - hvm_get_guest_time(v);
>>> +
>>> +    if ( offset ) {
>>> +        v->arch.hvm_vcpu.stime_offset += offset;
>>> +        /*
>>> +         * If hvm_vcpu.stime_offset is updated make sure to
>>> +         * also update vcpu time, since this value is used to
>>> +         * calculate the TSC.
>>> +         */
>>> +        if ( v == current )
>>> +            update_vcpu_system_time(v);
>>> +    }
>>>   }
>>>     static int pt_irq_vector(struct periodic_time *pt, enum 
>>> hvm_intsrc src)
>>
>> I have tested this patch and I have not been able to reproduce the 
>> guest stuck-clock problem we were seeing before (see *HVM Migration 
>> of domU on Qemu-upstream DM causes stuck system clock with ACPI* for 
>> details of the problem).
>> Note: this was tested without the temporary fix to our problem ( 
>> which is specifying tsc_mode='native_paravirt').
>
> Great, thanks Diana.
>
No problem.

On a side note, the patch applied cleanly to 4.2.2 and it works as 
expected too.
>  -George
>
--
Diana

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