From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [BUG] pgprot_noncached() is -NOT- safe for mapping vmalloc buffers into userspace Date: Fri, 25 Mar 2011 20:15:33 +1100 Message-ID: <1301044533.2402.478.camel@pasglop> References: <1301005008.2402.453.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from gate.crashing.org ([63.228.1.57]:32846 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755122Ab1CYJPv (ORCPT ); Fri, 25 Mar 2011 05:15:51 -0400 In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Takashi Iwai Cc: "linux-kernel@vger.kernel.org" , linuxppc-dev , linux-arch@vger.kernel.org, Matthew Evans On Fri, 2011-03-25 at 09:01 +0100, Takashi Iwai wrote: > > In fact, cache coherent architectures often don't support mapping memory > > uncached -at-all- so something like snd_pcm_lib_mmap_noncached() > > shouldn't exist, or at least be under arch control. There's no case > > where it's "always safe". There will almost always be a cache alias in > > the linear mapping unless special arch specific sauce has been applied. > > I see. I'll take your removal patch. > It should be applied to stable kernel, too, right? I suppose so :-) > > Now, there's another problem on top of that, which is that > > snd_pcm_default_mmap() will not work properly the "other way around" on > > powerpc, where the mapping -needs- to be uncached bcs you are running on > > a non cache coherent embedded CPU and trying to mmap DMA memory, but > > that's something that needs fixing inside powerpc by properly defining > > dma_mmap_coherent() & ARCH_HAS_DMA_MMAP_COHERENT (I thought we had added > > it a while back but it's not upstream, patch must have got lost). > > Mea culpa. I moved to a different team and have had little time for > the upstream development since then... That's ok, I did a new one, which you have noticed already anyways :-) > > We > > must also make sure we don't go down that path for vmalloc memory > > though. > > Yes. I haven't actually checked, but I assume that the test substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV In snd_pcm_default_mmap() takes care of that, please correct me if I'm wrong in which case we'll need something else there. > Your patch looks good. Thanks for taking care of this! Are you taking care of sending it upstream ? Cheers, Ben.