Re: [PATCH v3 7/8] arm64: exception: handle asynchronous SError interrupt

[Xiongfeng Wang]

Hi James,

On 2017/5/9 1:27, James Morse wrote:
> Hi Xiongfeng Wang,
> 
> On 28/04/17 03:55, Xiongfeng Wang wrote:
>>>>>> It is ok to just ignore the process following the ESB instruction in el0_sync, because the process will be sent SIGBUS signal.
>>>>
>>>> I don't understand. How will Linux know the process caused an error if we
>>>> neither take an SError nor read DISR_EL1 after an ESB?
> 
>> I think there may be some misunderstanding here. The ESB instruction is placed in kernel_entry
>> of el0_sync and el0_irq. For the el0_sync, such as an syscall from userspace, after ESB is executed,
>> we check whether DISR.A is set. If it is not set, we go on to process the syscall. If it is set, we
>> jump to sError vector and then just eret.
> 
> Ah, this looks like an early optimisation!
> 
> We can't assume that the SError will result in the processing being killed, the
> AET bits of the SError ISS Encoding (page D7-2284 of ARM-ARM DDI0487B.a), has a
> 'corrected' error encoding.
> For these I would expect the SError-vector C code to do nothing and return to
> where it came from. In this case the syscall should still be run.
> 
Yes, it makes sense, so we should add a return value for the do_sei handler.

Thanks,
Wang Xiongfeng