[PATCH] riscv: fix race when vmap stack overflow

[Tong Tiangen]

在 2022/10/21 16:36, Andrea Parri 写道:
>>>> +     atomic_set_release(&spin_shadow_stack, 0);
>>>
>>> Have not really looked the details: should there be a matching acquire?
>>
>> I use atomic_set_release here, because I need earlier memory
>> operations finished to make sure the sp is ready then set the spin
>> flag.
>>
>> The following memory operations order is not important, because we
>> just care about sp value.
>>
>> Also, we use relax amoswap before, because sp has naturelly
>> dependency. But giving them RCsc is okay here, because we don't care
>> about performance here.
> 
> Thanks for the clarification.
> 
> I'm not really suggesting to add unneeded synchronization, even more
> so in local/private constructs as in this case.  It just felt odd to
> see the release without a pairing acquire, so I asked.  ;-)
> 
> Thanks,
>    Andrea
> 
> 
>> eg:
>>   handle_kernel_stack_overflow:
>> +1:     la sp, spin_shadow_stack
>> +       amoswap.w.aqrl sp, sp, (sp)
>> +       bnez sp, 1b
>> +
>> ....
>> +     smp_store_release(&spin_shadow_stack, 0);
>> +     smp_mb();
> 

Hi Andrea, Zhang, Guo:
	Consider this implementation:)

	smp_store_mb(&spin_shadow_stack, 0);

Thanks,
Tong.
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