[BUG] pgprot_noncached() is -NOT- safe for mapping vmalloc buffers into userspace
benh at kernel.crashing.org
Fri Mar 25 20:15:33 EST 2011
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.
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 ?
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