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

[Sergei Shtylyov]

Hello.

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

> > 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?

   Yes, it appears so. :-)

WBR, Sergei

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