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

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Date:	Sat, 31 Jan 2015 12:14:29 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Greg KH <gregkh@...uxfoundation.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<linux-usb@...r.kernel.org>
Subject: Re: [PATCH] pci-dma: Fix x86 dma_alloc_coherent to fully clear all
 pages returned

On Fri, 30 Jan 2015, Andi Kleen wrote:

> > 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?
> 
> How would you find them all?
> 
> We don't even know which place in XHCI is the culprit here.

It shouldn't be too hard to find, expecially if the fault can easily 
be reproduced.

There are only about half a dozen calls to dma_alloc_coherent in the
xhci-hcd driver.  Just add 64 KB to the requested memory size in each
of them.  Then one-by-one (or using bisection) remove the extra size
and see which spots trigger the fault.

Alan Stern

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