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SubjectRe: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all pages returned
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On Fri, 2015-01-30 at 14:07 -0800, Greg KH wrote:
> On Fri, Jan 30, 2015 at 02:01:58PM -0800, Tim Chen wrote:
> > On Fri, 2015-01-30 at 11:58 -0800, Greg KH wrote:
> >
> > >
> > > Shouldn't this go to stable trees too?
> > >
> >
> > Yes. Added the stable tag in updated patch that's resent.
> >
> > > Also, why is the xhci driver not asking for the memory it is going to
> > > need? If it wants to use the full page, shouldn't it ask for it?
> > >
> >
> > I agree that xhci should have done that, but it didn't. Commit
> > d92ef66c4f8f ("x86: make dma_alloc_coherent() return zeroed memory
> > if CMA is enabled") changed the behavior of dma_alloc_coherent
> > by clearing only the memory being asked for.
> >
> > So for backward compatibility, clearing the pages
> > completely to revert to dma_alloc_coherent's original
> > behavior is probably the safe thing to do.
>
> We don't "need" any backward compatility, why not fix the broken drivers
> that are using memory outside of what they are asking for? That's not
> ok no matter what, right?

Not disagreeing with you. I'll be equally happy if the xhci folks
can fix the driver. Mathias?

Tim



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