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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