linux-kernel - Re: [PATCH] HID: sony: Enable Gasia third-party PS3 controllers

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Date:	Thu, 19 Mar 2015 10:54:22 +0100
From:	Oliver Neukum <oneukum@...e.de>
To:	Pavel Machek <pavel@....cz>
Cc:	Jiri Kosina <jkosina@...e.cz>, Lauri Kasanen <cand@....com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	ao2@....it, AndrewD207@....com
Subject: Re: [PATCH] HID: sony: Enable Gasia third-party PS3 controllers

On Thu, 2015-03-19 at 10:38 +0100, Pavel Machek wrote:
> On Thu 2015-03-19 10:14:21, Oliver Neukum wrote:
> > On Mon, 2015-03-16 at 22:37 +0100, Jiri Kosina wrote:

> > > Are you sure CONFIG_DMA_API_DEBUG wouldn't warn here?
> > 
> > As far as I can tell, it will not warn. The problem is not in the
> > mapping itself. That is usually legitimate. The problem arises
> > because the buffer doesn't have a cacheline of its own. Thus the
> > memory corruption happens after the IO operation has started.
> 
> Nasty. Would WARN_ON(buffer & CACHELINE_SIZE-1) do at least part of

No. It is perfectly legitimate to put your buffer at an offset
or to combine buffers provided you don't use them at the same
time.

> the trick? Alternatively, could we call ksize() on the object, and
> fail if it is not big enough?

What object? We have a pointer to a memory location.

> Alternatively, we could create "allocate_for_usb" function, and only
> take pointers allocated by that function in usb functions. That would
> also teach people the problem exists...

No, this problem is not limited to USB.

	Regards
		Oliver


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