Messages in this thread | | | Date | Sat, 31 Jan 2015 00:03:28 +0300 | From | Sergei Shtylyov <> | Subject | Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all pages returned |
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On 01/30/2015 10:54 PM, Tim Chen wrote:
> 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 and froze usb:
> 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> > --- > 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..534470f 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-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;
WBR, Sergei
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