Re: [PATCH v4 04/12] iommu/vt-d: Add 256-bit invalidation descriptor support

[Lu Baolu <baolu.lu@linux.intel.com>]

On 11/8/18 1:48 PM, Liu, Yi L wrote:
>> From: Liu, Yi L
>> Sent: Thursday, November 8, 2018 1:45 PM
>>>>>>> +			memcpy(desc, qi->desc + (wait_index << shift),
>>>>>>
>>>>>> Would "memcpy(desc, (unsigned long long) (qi->desc +  (wait_index
>>>>>> << shift)," be more safe?
>>>>>
>>>>> Can that be compiled? memcpy() requires a "const void *" for the
>>>>> second
>>> parameter.
>>>>> By the way, why it's safer with this casting?
>>>>
>>>> This is just an example. My point is the possibility that "qi->desc
>>>> + (wait_index <<
>>> shift)"
>>>> would be treated as "qi->desc plus (wait_index <<
>>>> shift)*sizeof(*qi->desc)". Is it possible for kernel build?
>>>
>>> qi->desc is of type of "void *".
>>
>> no, I don’t think so... Refer to the code below. Even it has no correctness issue her,
>> It's not due to qi->desc is "void *" type...
>>
>> struct qi_desc {
>> -	u64 low, high;
>> +	u64 qw0;
>> +	u64 qw1;
>> +	u64 qw2;
>> +	u64 qw3;
>> };
> 
> Oops, just see you modified it to be "void *" in this patch. Ok, then this is fair enough.

Yes. :-)

Best regards,
Lu Baolu