linux-kernel - Re: ALSA: vmalloc buffers should use normal mmap

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Date:	Fri, 25 Mar 2011 11:14:48 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: ALSA: vmalloc buffers should use normal mmap

At Fri, 25 Mar 2011 17:51:54 +1100,
Benjamin Herrenschmidt wrote:
> 
> It's a big no-no to use pgprot_noncached() when mmap'ing such buffers
> into userspace since they are mapped cachable in kernel space.
> 
> This can cause all sort of interesting things ranging from to garbled
> sound to lockups on various architectures. I've observed that usb-audio
> is broken on powerpc 4xx for example because of that.
> 
> Also remove the now unused snd_pcm_lib_mmap_noncached(). It's
> an arch business to know when to use uncached mappings, there's
> already hacks for MIPS inside snd_pcm_default_mmap() and other
> archs are supposed to use dma_mmap_coherent().
> 
> (See my separate patch that adds dma_mmap_coherent() to powerpc)
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> CC: Takashi Iwai <tiwai@...e.de>

Applied now to sound git tree.  Thanks.


Takashi

> ---
>  include/sound/pcm.h     |    4 +---
>  sound/core/pcm_native.c |    9 ---------
>  2 files changed, 1 insertions(+), 12 deletions(-)
> 
> diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> index 430a9cc..e1bad11 100644
> --- a/include/sound/pcm.h
> +++ b/include/sound/pcm.h
> @@ -1031,9 +1031,7 @@ int snd_pcm_lib_mmap_iomem(struct snd_pcm_substream *substream, struct vm_area_s
>  #define snd_pcm_lib_mmap_iomem	NULL
>  #endif
>  
> -int snd_pcm_lib_mmap_noncached(struct snd_pcm_substream *substream,
> -			       struct vm_area_struct *area);
> -#define snd_pcm_lib_mmap_vmalloc	snd_pcm_lib_mmap_noncached
> +#define snd_pcm_lib_mmap_vmalloc NULL
>  
>  static inline void snd_pcm_limit_isa_dma_size(int dma, size_t *max)
>  {
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 2d99c37..7639407 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -3194,15 +3194,6 @@ int snd_pcm_lib_mmap_iomem(struct snd_pcm_substream *substream,
>  EXPORT_SYMBOL(snd_pcm_lib_mmap_iomem);
>  #endif /* SNDRV_PCM_INFO_MMAP */
>  
> -/* mmap callback with pgprot_noncached */
> -int snd_pcm_lib_mmap_noncached(struct snd_pcm_substream *substream,
> -			       struct vm_area_struct *area)
> -{
> -	area->vm_page_prot = pgprot_noncached(area->vm_page_prot);
> -	return snd_pcm_default_mmap(substream, area);
> -}
> -EXPORT_SYMBOL(snd_pcm_lib_mmap_noncached);
> -
>  /*
>   * mmap DMA buffer
>   */
> 
> 
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