From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 2867C1007D5 for ; Fri, 25 Mar 2011 20:15:45 +1100 (EST) Subject: Re: [BUG] pgprot_noncached() is -NOT- safe for mapping vmalloc buffers into userspace From: Benjamin Herrenschmidt To: Takashi Iwai In-Reply-To: References: <1301005008.2402.453.camel@pasglop> Content-Type: text/plain; charset="UTF-8" Date: Fri, 25 Mar 2011 20:15:33 +1100 Message-ID: <1301044533.2402.478.camel@pasglop> Mime-Version: 1.0 Cc: linux-arch@vger.kernel.org, linuxppc-dev , "linux-kernel@vger.kernel.org" , Matthew Evans List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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.