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

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Message-ID: <20150319101203.GA22127@amd>
Date:	Thu, 19 Mar 2015 11:12:03 +0100
From:	Pavel Machek <pavel@....cz>
To:	Oliver Neukum <oneukum@...e.de>
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 10:54:22, Oliver Neukum wrote:
> 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.

Legitimate: yes. Is anyone doing it? And will not they see exactly the
same data corruption with the aliasing data?

> > 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.

Well.. Recognize that just because you have a pointer does not mean
you can pass it to certain functions.

Maybe those functions should not be taking pointers in the first
place....

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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