netdev - Re: [linux-next PATCH] mlx5: wrong page mask if CONFIG_ARCH_DMA_ADDR_T

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Date:	Mon, 13 Apr 2015 17:19:38 +0800
From:	Honggang LI <honli@...hat.com>
To:	Eli Cohen <eli@...lanox.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [linux-next PATCH] mlx5: wrong page mask if
  CONFIG_ARCH_DMA_ADDR_T_64BIT enabled for 32Bit architectures

On Mon, Apr 13, 2015 at 06:47:11AM +0000, Eli Cohen wrote:
>  On Mon, Apr 13, 2015 at 08:33:33AM +0800, Honggang LI wrote:
> > 
> > Yes, replaced all of the PAGE_MASK in the file. Please see attched new
> > patch.
> > 
> 
> I think you need to send the new patch inline in your email.
> 

I will resent the patch.

> > > 
> > > @@ -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.
> > 
> 
> Sorry, I still don't understand the issue here. MLX5_NUM_4K_IN_PAGE is
> not a mask and will always get the correct value which is fairly
> small.

Sorry. It was a typo. It should be MLX5_U64_4K_PAGE_MASK.


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