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

[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.


>   
>   	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;
>   	}
>