[PATCH v2 5/6] crypto/fsl: instantiate the RNG with prediciton resistance

[Michael Walle]

Am 2020-06-19 18:54, schrieb Horia Geantă:
> On 6/19/2020 7:37 PM, Horia Geanta wrote:
>> On 6/17/2020 11:48 PM, Michael Walle wrote:
>>> Am 2020-06-17 21:15, schrieb Horia Geantă:
>>>> On 6/4/2020 6:48 PM, Michael Walle wrote:
>>>>> +
>>>>> +	desc = memalign(ARCH_DMA_MINALIGN, desc_size);
>>>>> +	if (!desc) {
>>>>> +		debug("cannot allocate RNG init descriptor memory\n");
>>>>> +		return -ENOMEM;
>>>>> +	}
>>>>> +
>>>>> +	for (sh_idx = 0; sh_idx < RNG4_MAX_HANDLES; sh_idx++) {
>>>>> +		/*
>>>>> +		 * If the corresponding bit is set, then it means the state
>>>>> +		 * handle was initialized by us, and thus it needs to be
>>>>> +		 * deinitialized as well
>>>>> +		 */
>>>>> +
>>>>> +		if (state_handle_mask & RDSTA_IF(sh_idx)) {
>>>>> +			/*
>>>>> +			 * Create the descriptor for deinstantating this state
>>>>> +			 * handle.
>>>>> +			 */
>>>>> +			inline_cnstr_jobdesc_rng_deinstantiation(desc, sh_idx);
>>>>> +			flush_dcache_range((unsigned long)desc,
>>>>> +					   (unsigned long)desc + desc_size);
>>>> Shouldn't this be roundup(desc_size, ARCH_DMA_MINALIGN) instead of
>>>> desc_size?
>>> 
>>> I've seen the same idioms sometimes, but it wasn't clear to me why 
>>> that
>>> would
>>> be needed; the hardware only uses the desc_size, right?
>>> 
>> Yes, HW will use only [desc, desc + desc_size].
>> 
>> I think this is needed to avoid cacheline sharing issues
>> on non-coherent platforms: CPU needs to make sure a larger area
>> is written back to memory and corresponding cache lines are 
>> invalidated.
>> 
>> Looking at flush_dcache_range() implementation, it does its own 
>> rounding,
>> based on CTR_EL0[DminLine] - "smallest data cache line size".
>> I guess this value might be smaller than ARCH_DMA_MINALIGN,
>> hence the explicit rounding to ARCH_DMA_MINALIGN is needed.
>> 
> Btw, I think
> 	desc = memalign(ARCH_DMA_MINALIGN, desc_size);
> needs to be replaced with
> 	desc = malloc_cache_aligned(desc_size);

But then the rounding is not needed, right? I mean there can't
be any other malloc() which might allocate memory in the same
cache line.

-michael