Re: [linux-next PATCH] mlx5: wrong page mask if CONFIG_ARCH_DMA_ADDR_T_64BIT enabled for 32Bit architectures

From: Honggang LI
Date: Sun Apr 12 2015 - 20:33:48 EST

On Sun, Apr 12, 2015 at 03:04:16PM +0000, Eli Cohen wrote:
> Good catch, thanks!
> There are more places in this file where PAGE_MASK is wrongly used. Need to fix them as well.

Yes, replaced all of the PAGE_MASK in the file. Please see attched new

> Also, see below [Eli]
> @@ -241,7 +243,7 @@ static void free_4k(struct mlx5_core_dev *dev, u64 addr) static int alloc_system_page(struct mlx5_core_dev *dev, u16 func_id) {
> struct page *page;
> - u64 addr;
> + u64 addr = 0; [Eli] Why is this required?

For 32bit architectures, if CONFIG_ARCH_DMA_ADDR_T_64BIT disabled and
physical memory is less than 4GB, dma_map_page will return an u32 integer
less than 0xffff_ffff. And if addr had been initialized with random
rubbish in the stack of alloc_system_page, the high four bytes is
unpredictable. The new mask, MLX5_NUM_4K_IN_PAGE, will reserve the high
four bytes. So, free_4k/find_fw_page will randomly failed.


> int err;
> int nid = dev_to_node(&dev->pdev->dev);
> --