Re: [RFC v1 34/38] target/arm: cpu: only initialize TCG gt timers under CONFIG_TCG

[Claudio Fontana]

On 2/22/21 4:34 PM, Alex Bennée wrote:
> 
> Claudio Fontana <cfontana@suse.de> writes:
> 
>> From: Claudio Fontana <cfontana@centriq4.arch.suse.de>
>>
>> KVM has its own cpu->kvm_vtime.
>>
>> Adjust cpu vmstate by putting unused fields instead of the
>> VMSTATE_TIMER_PTR when TCG is not available.
>>
>> Signed-off-by: Claudio Fontana <cfontana@suse.de>
>> ---
>>  target/arm/cpu.c     | 4 +++-
>>  target/arm/machine.c | 5 +++++
>>  2 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>> index 1d81a1e7ac..b929109054 100644
>> --- a/target/arm/cpu.c
>> +++ b/target/arm/cpu.c
>> @@ -1322,6 +1322,7 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
>> **errp)
>>          }
>>      }
>>  
>> +#ifdef CONFIG_TCG
>>      {
>>          uint64_t scale;
>>  
>> @@ -1347,7 +1348,8 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
>> **errp)
>>          cpu->gt_timer[GTIMER_HYPVIRT] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
>>                                                    arm_gt_hvtimer_cb, cpu);
>>      }
>> -#endif
>> +#endif /* CONFIG_TCG */
>> +#endif /* !CONFIG_USER_ONLY */
>>  
>>      cpu_exec_realizefn(cs, &local_err);
>>      if (local_err != NULL) {
>> diff --git a/target/arm/machine.c b/target/arm/machine.c
>> index 666ef329ef..13d7c6d930 100644
>> --- a/target/arm/machine.c
>> +++ b/target/arm/machine.c
>> @@ -822,8 +822,13 @@ const VMStateDescription vmstate_arm_cpu = {
>>          VMSTATE_UINT32(env.exception.syndrome, ARMCPU),
>>          VMSTATE_UINT32(env.exception.fsr, ARMCPU),
>>          VMSTATE_UINT64(env.exception.vaddress, ARMCPU),
>> +#ifdef CONFIG_TCG
>>          VMSTATE_TIMER_PTR(gt_timer[GTIMER_PHYS], ARMCPU),
>>          VMSTATE_TIMER_PTR(gt_timer[GTIMER_VIRT], ARMCPU),
>> +#else
>> +        VMSTATE_UNUSED(sizeof(QEMUTimer *)),
>> +        VMSTATE_UNUSED(sizeof(QEMUTimer *)),
>> +#endif /* CONFIG_TCG */
> 
> I'm not sure this is correct - VMSTATE_TIMER_PTR chases the links to
> just expose expired time but QEMUTimer has more in it than that. Paolo


I am not sure I follow can you state more precisely where the issue could be?

it's not a VMSTATE_TIMER, it's a VMSTATE_TIMER_PTR,
it ends up in VMSTATE_POINTER where a single pointer is assigned;

so if we don't use gt_timer at all (as is the case with !CONFIG_TCG), we just
need to ensure that an unused number is there to assign, migrating from old to 
new version?


> suggested a straight VMSTATE_UNUSED(8) on IRC but I wonder if it would
> be better to have a VMSTATE_UNUSED_TIMER?
> 
> I don't think there is an impact for Xen because I'm fairly certain
> migration isn't a thing we do - but I'll double check.
> 

Thanks Alex, that would be helpful,
if Xen uses gt_timer in any way I would not want to unwillingly break it.

Thanks,

Claudio