linux-kernel - Re: USB transfer_buffer allocations on 64bit systems

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <201004090804.36213.oliver@neukum.org>
Date:	Fri, 9 Apr 2010 08:04:35 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Daniel Mack <daniel@...aq.de>, linux-kernel@...r.kernel.org,
	Pedro Ribeiro <pedrib@...il.com>, akpm@...ux-foundation.org,
	Greg KH <gregkh@...e.de>, alsa-devel@...a-project.org,
	linux-usb@...r.kernel.org
Subject: Re: USB transfer_buffer allocations on 64bit systems

Am Freitag, 9. April 2010 00:20:36 schrieb Alan Stern:
> > > That would work, but it doesn't match the way existing drivers use the
> > > interface.  For example, the audio driver allocates a 16-byte coherent
> > > buffer and then uses four bytes from it for each of four different 
> > > URBs.
> > 
> > That will not work with any fallback that does not yield a coherent buffer.
> 
> What you mean isn't entirely clear.  But it certainly does work in 
> various circumstances that don't yield coherent buffers.  For example, 
> it works if the controller uses PIO instead of DMA.  It also works if 
> the controller uses DMA and the URBs have to be bounced.

It'll work on x86. On incoherent architectures this violates the cacheline
rules for DMA-mapping if you have to bounce. So it seems to me that
if you want to share a buffer between URBs, it must be coherent.

	Regards
		Oliver
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/