From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Mon, 02 Feb 2015 19:39:18 +0300
From: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
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To: Jiri Slaby <jslaby@suse.cz>, Tim Chen <tim.c.chen@linux.intel.com>
CC: "H. Peter Anvin" <hpa@zytor.com>,
	Akinobu Mita <akinobu.mita@gmail.com>,
	Mathias Nyman <mathias.nyman@linux.intel.com>,
	Andi Kleen <andi@firstfloor.org>, Ingo Molnar <mingo@elte.hu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-usb@vger.kernel.org, stable <stable@vger.kernel.org>
Subject: Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all
 pages returned
References: <1422647641.9530.2.camel@schen9-desk2.jf.intel.com>	 <54CBF1A0.9080005@cogentembedded.com> <1422654849.9530.8.camel@schen9-desk2.jf.intel.com> <54CF8374.80704@suse.cz>
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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