[PATCH] drm/amd/amdgpu: cast mem->num_pages to 64-bits when shifting

[Christian König]

Am 17.06.19 um 21:15 schrieb Kuehling, Felix:
> Looks good to me. One cosmetic comment inline. With that fixed this
> patch is Reviewed-by:  Felix Kuehling <Felix.Kuehling at amd.com>
>
> On 2019-06-14 12:51 p.m., StDenis, Tom wrote:
>> On 32-bit hosts mem->num_pages is 32-bits and can overflow
>> when shifted.  Add a cast to avoid this.
>>
>> Signed-off-by: Tom St Denis <tom.stdenis at amd.com>
>> ---
>>    drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 8 +++++---
>>    1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
>> index c963ad86072e..31895d3c33de 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
>> @@ -279,14 +279,16 @@ static int amdgpu_vram_mgr_new(struct ttm_mem_type_manager *man,
>>    	uint64_t vis_usage = 0;
>>    	unsigned i;
>>    	int r;
>> +	uint64_t mem_bytes;
> Christian likes the "upside-down christmas tree" to help readability of
> local variable declarations.

Ah, yeah. Thanks for the note.

I actually don't care about that much, but I always get rejects from 
upstream subsystem maintainers if I don't do this.

It's most likely not even documented somewhere,
Christian.

>
>
>>    
>>    	lpfn = place->lpfn;
>>    	if (!lpfn)
>>    		lpfn = man->size;
>>    
>>    	/* bail out quickly if there's likely not enough VRAM for this BO */
>> -	if (atomic64_add_return(mem->num_pages << PAGE_SHIFT, &mgr->usage) > adev->gmc.mc_vram_size) {
>> -		atomic64_sub(mem->num_pages << PAGE_SHIFT, &mgr->usage);
>> +	mem_bytes = (u64)mem->num_pages << PAGE_SHIFT;
>> +	if (atomic64_add_return(mem_bytes, &mgr->usage) > adev->gmc.mc_vram_size) {
>> +		atomic64_sub(mem_bytes, &mgr->usage);
>>    		mem->mm_node = NULL;
>>    		return 0;
>>    	}
>> @@ -308,7 +310,7 @@ static int amdgpu_vram_mgr_new(struct ttm_mem_type_manager *man,
>>    	nodes = kvmalloc_array((uint32_t)num_nodes, sizeof(*nodes),
>>    			       GFP_KERNEL | __GFP_ZERO);
>>    	if (!nodes) {
>> -		atomic64_sub(mem->num_pages << PAGE_SHIFT, &mgr->usage);
>> +		atomic64_sub(mem_bytes, &mgr->usage);
>>    		return -ENOMEM;
>>    	}
>>    
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