Re: [Qemu-devel] [PATCH v1 11/16] target-arm: Don't take interrupts targeting lower ELs

[Aggeler Fabian]

On 09 Jun 2014, at 01:43, Edgar E. Iglesias <address@hidden> wrote:

> On Sun, Jun 08, 2014 at 03:51:24PM +0000, Aggeler  Fabian wrote:
>> 
>> On 30 May 2014, at 09:28, Edgar E. Iglesias <address@hidden> wrote:
>> 
>>> From: "Edgar E. Iglesias" <address@hidden>
>>> 
>>> Signed-off-by: Edgar E. Iglesias <address@hidden>
>>> ---
>>> target-arm/cpu.h | 7 +++++++
>>> 1 file changed, 7 insertions(+)
>>> 
>>> diff --git a/target-arm/cpu.h b/target-arm/cpu.h
>>> index 9eddcc1..66c58bd 100644
>>> --- a/target-arm/cpu.h
>>> +++ b/target-arm/cpu.h
>>> @@ -1133,6 +1133,13 @@ bool write_cpustate_to_list(ARMCPU *cpu);
>>> static inline bool arm_excp_unmasked(CPUState *cs, unsigned int excp_idx)
>>> {
>>>    CPUARMState *env = cs->env_ptr;
>>> +    unsigned int cur_el = arm_current_pl(env);
>>> +    unsigned int target_el = arm_excp_target_el(cs, excp_idx);
>>> +
>>> +    /* Don't take exceptions if they target a lower EL.  */
>>> +    if (cur_el > target_el) {
>>> +        return false;
>>> +    }
>> 
>> Hi Edgar
> 
> Hi Fabian,
> 
>> 
>> When making arm_excp_unmasked() reflect tables D1-13, D1-14, D1-15 
>> and G1-18, G1-19 in ARM ARMv8 this should not be necessary if I am 
>> not mistaken. Cases in which target_el is lower than cur_el are marked with 
>> a P (pending) in the table. Or am I missing something interpreting the
>> tables?
> 
> This function is called to check if we can take a pending interrupt or
> exception with current CPU state. It does not clear pending exceptions.
> In this case, if the target_el is lower than the current EL we return false
> and leave the exception pending (to be taken later).

I know, but what I want to say is, doesn’t the table which I mentioned reflect 
this
by marking it with a P for pending for cases where target_el would be lower than
the current EL it is taken from?

So if we handle these cases in arm_excp_unmasked() we don’t need to call 
arm_excp_target_el() to check.

> 
>> 
>> I extended your arm_excp_unmasked() and arm_excp_target_el() to reflect 
>> the behaviour shown in the tables in ARM ARMv8 and ARM ARMv7. I will 
>> send them with the TZ patches.
> 
> Great, thanks.
> 
> Cheers,
> Edgar
> 
> 
>> 
>> Best,
>> Fabian
>> 
>>> 
>>>    switch (excp_idx) {
>>>    case EXCP_FIQ:
>>> -- 
>>> 1.8.3.2