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

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 02/02/2015 05:02 PM, Jiri Slaby wrote:

>> From: Tim Chen <tim.c.chen@linux.intel.com>
>> 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@linux.intel.com>
>> Cc: <stable@vger.kernel.org> # 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?

    Yes, it appears so. :-)

WBR, Sergei