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Date:   Tue, 9 Jun 2020 11:17:27 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Christoph Hellwig <hch@lst.de>,
        David Rientjes <rientjes@google.com>,
        "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>,
        alsa-devel@alsa-project.org, bp@alien8.de, hch@infradead.org,
        hpa@zytor.com, linux-kernel@vger.kernel.org, mingo@redhat.com,
        Pavel Machek <pavel@ucw.cz>, perex@perex.cz,
        tglx@linutronix.de, tiwai@suse.com, x86@kernel.org
Subject: Re: next-0519 on thinkpad x60: sound related? window manager crash
Message-ID: <20200609091727.GA23814@lst.de>
References: <20200520111136.GA3802@amd> <1591545088.74ii116nf2.none@localhost> <20200608061950.GA17476@lst.de> <1591624340.z01ejtod28.none@localhost> <alpine.DEB.2.22.394.2006081928070.148886@chino.kir.corp.google.com> <20200609054306.GA9606@lst.de> <s5hsgf4irzt.wl-tiwai@suse.de> <20200609084305.GA21671@lst.de> <s5hlfkwip1h.wl-tiwai@suse.de>
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On Tue, Jun 09, 2020 at 11:09:14AM +0200, Takashi Iwai wrote:
> On Tue, 09 Jun 2020 10:43:05 +0200,
> Christoph Hellwig wrote:
> > 
> > On Tue, Jun 09, 2020 at 10:05:26AM +0200, Takashi Iwai wrote:
> > > > >From the disassembly it seems like a vmalloc allocation is NULL, which
> > > > seems really weird as this patch shouldn't make a difference for them,
> > > > and I also only see a single places that allocates the field, and that
> > > > checks for an allocation failure.  But the sound code is a little
> > > > hard to unwind sometimes.
> > > 
> > > It's not clear which sound device being affected, but if it's
> > > HD-audio on x86, runtime->dma_area points to a vmapped buffer from
> > > SG-pages allocated by dma_alloc_coherent().
> > > 
> > > OTOH, if it's a USB-audio, runtime->dma_area is a buffer by
> > > vmalloc().
> > 
> > Err, you can't just vmap a buffer returned from dma_alloc_coherent,
> > dma_alloc_coherent returns values are opaque and can't be used
> > for virt_to_page.  Whatever that code did has already been broken
> > per the DMA API contract and on many architectures and just happend
> > to work on x86 by accident.
> 
> Hmm, that's bad.
> 
> How would be a proper way to get the virtually mapped SG-buffer pages
> with coherent memory?  (Also allowing user-space mmap, too)

dma_mmap_coherent / dma_mmap_attrs for userspace.  We don't really
have a good way for kernel space mappings.