Re: [Qemu-devel] [PATCH v1 7/7] target-arm: Call the pmccntr_sync function when swapping ELs

[Peter Crosthwaite]

On Wed, Jun 25, 2014 at 8:39 AM, Alistair Francis
<address@hidden> wrote:
> On Wed, Jun 25, 2014 at 1:55 AM, Christopher Covington
> <address@hidden> wrote:
>> On 06/23/2014 09:12 PM, Alistair Francis wrote:
>>> Call the new pmccntr_sync() function when there is a possibility
>>> of swapping ELs (I.E. when there is an exception)
>>>
>>> Signed-off-by: Alistair Francis <address@hidden>
>>> ---
>>>
>>>  target-arm/helper-a64.c |    5 +++++
>>>  target-arm/helper.c     |    7 +++++++
>>>  target-arm/op_helper.c  |    6 ++++++
>>>  3 files changed, 18 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/target-arm/helper-a64.c b/target-arm/helper-a64.c
>>> index 2b4ce6a..b61174f 100644
>>> --- a/target-arm/helper-a64.c
>>> +++ b/target-arm/helper-a64.c
>>> @@ -446,6 +446,8 @@ void aarch64_cpu_do_interrupt(CPUState *cs)
>>>      target_ulong addr = env->cp15.vbar_el[1];
>>>      int i;
>>>
>>> +    pmccntr_sync(env);
>>> +
>>>      if (arm_current_pl(env) == 0) {
>>>          if (env->aarch64) {
>>>              addr += 0x400;
>>> @@ -484,6 +486,7 @@ void aarch64_cpu_do_interrupt(CPUState *cs)
>>>          addr += 0x100;
>>>          break;
>>>      default:
>>> +        pmccntr_sync(env);
>>>          cpu_abort(cs, "Unhandled exception 0x%x\n", cs->exception_index);

Not sure you need this, there is not much point in causing your side
effects right before an assertion (via cpu_abort).

>>>      }
>>>
>>> @@ -511,4 +514,6 @@ void aarch64_cpu_do_interrupt(CPUState *cs)
>>>
>>>      env->pc = addr;
>>>      cs->interrupt_request |= CPU_INTERRUPT_EXITTB;
>>> +
>>> +    pmccntr_sync(env);
>>>  }
>>
>> The double calls seem unwieldy. I think it could be made into a single
>> function call if there was access, perhaps as a second parameter or maybe as 
>> a
>> static variable, to both the previous and current state so the function could
>> tell whether there is no transition, enable->disable, or disable->enable.
>>
>
> The problem with a parameter is that the state of the enabled register needs
> to be saved at the start of any code that will enable/disable the register. So
> it ends up being just as messy.
>
> Static variables won't work if there are multiple CPUs. I guess an
> array of statics
> could work, but I don't like that method
>
> I feel that just calling the function twice ends up being neat and
> works pretty well
>

Theres a third option. Create a new function that explicitly changes EL:

arm_change_el(int new) {
    sync();
    env->el = new;
    sync();
}

And update the interrupt path functions to use it instead of direct
env manipulation.

The advantage of this, is others can also add el switching side
effects in one place. I doubt this is the last time we will want to
trap EL changes for system level side effects.

Regards,
Peter

>> Christopher
>>
>> --
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>> hosted by the Linux Foundation.
>>
>