[PATCH 1/4] drm/ttm: add multihop infrastrucutre (v2)

[Christian König]

Am 09.11.20 um 16:16 schrieb Ville Syrjälä:
> On Wed, Nov 11, 2020 at 06:13:02PM +0100, Christian König wrote:
>> Am 09.11.20 um 01:54 schrieb Dave Airlie:
>>> @@ -1432,15 +1479,18 @@ int ttm_bo_swapout(struct ttm_operation_ctx *ctx)
>>>    	if (bo->mem.mem_type != TTM_PL_SYSTEM) {
>>>    		struct ttm_operation_ctx ctx = { false, false };
>>>    		struct ttm_resource evict_mem;
>>> +		struct ttm_place hop = {};
>> Please always use memset() if you want to zero initialize something in
>> the kernel, we had enough trouble with that.
> What trouble is that? I've not heard of anything, and we use
> ={} quite extensively in drm land.

={} initializes only named fields, not padding.

The result is that for example when doing a hash or CRC of a structure 
you can come up with different results depending on the architecture 
and/or structure layout.

Another problem are information leaks from the kernel to userspace 
because of this.

Because of this Mesa for example strongly discourages using ={} for 
zeroing a structure.

Regards,
Christian.