Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all pages returned

[Jiri Slaby]

On 01/30/2015, 10:54 PM, Tim Chen wrote:
> On Sat, 2015-01-31 at 00:03 +0300, Sergei Shtylyov wrote:
>> On 01/30/2015 10:54 PM, Tim Chen wrote:
> 
>>>
>>>   		return NULL;
>>>   	}
>>> +	/* round up to full page size */
>>> +	size = (((size-1) >> PAGE_SHIFT) + 1) * PAGE_SIZE;
>>
>>     This is quite suboptimal formula, we can do without shifts and 
>> multiplications (hopefully, still converted to shifts by gcc):
>>
>> 	size = (size + ~PAGE_MASK) & PAGE_MASK;
> 
> Agree.  I've updated patch below
> 
> Thanks.
> 
> Tim
> 
> --->8---
> 
> From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Subject: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all pages returned
> 
> 
> Commit d92ef66c4f8f ("x86: make dma_alloc_coherent() return zeroed memory
> if CMA is enabled") changed the dma_alloc_coherent page clearance from
> using an __GFP_ZERO in page allocation to not setting the flag but doing
> an explicit memory clear at the end.
> 
> However the memory clear only covered the memory size that
> was requested, but may not be up to the full extent of the
> last page, if the total pages returned exceed the
> memory size requested.  This behavior has caused problem with XHCI
> and caused it to hang:
> 
> kernel: xhci_hcd 0000:00:14.0: Stopped the command ring failed, maybe the host is dead
> kernel: xhci_hcd 0000:00:14.0: Abort command ring failed
> kernel: xhci_hcd 0000:00:14.0: HC died; cleaning up
> kernel: xhci_hcd 0000:00:14.0: Error while assigning device slot ID
> kernel: xhci_hcd 0000:00:14.0: Max number of devices this xHCI host supports is 64.
> 
> Other drivers may have similar issue if it assumes that the pages
> allocated are completely zeroed.
> 
> This patch ensures that the pages returned are fully cleared.
> 
> Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 3.16+
> 
> ---
>  arch/x86/kernel/pci-dma.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index a25e202..e9d8dee 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -125,6 +125,8 @@ again:
>  
>  		return NULL;
>  	}
> +	/* round up to full page size */
> +	size = (size + ~PAGE_MASK) & PAGE_MASK;

Hi, is this an open-coded version of PAGE_ALIGN?

>  	memset(page_address(page), 0, size);
>  	*dma_addr = addr;
>  	return page_address(page);
> 


-- 
js
suse labs
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