linux-kernel - Re: [PATCH v1 ] ALSA: core: memalloc: add page alignment for iram

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Date:   Thu, 17 Dec 2020 17:28:40 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     alsa-devel@...a-project.org, gustavoars@...nel.org,
        linux-kernel@...r.kernel.org, shengjiu.wang@....com,
        tiwai@...e.com, pierre-louis.bossart@...ux.intel.com,
        xiang@...nel.org, Robin Gong <yibin.gong@....com>,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v1 ] ALSA: core: memalloc: add page alignment for iram

On Thu, 17 Dec 2020 16:38:22 +0100,
Lars-Peter Clausen wrote:
> 
> >> Maybe what we need is a check that runtime->dma_area is page aligned
> >> and runtime->dma_bytes is a multiple of PAGE_SIZE. With a warning at
> >> first and then turn this into a error a year later or so.
> > OK, how about the following instead?
> > Just check SNDRV_PCM_INFO_MMAP in runtime->info; if this is set, the
> > buffer size must be aligned with the page size, and we are safe to
> > extend the size to clear.
> >
> > So the revised fix is much simpler, something like below.
> 
> I think this will work for the leaking data issue.
> 
> But it will not help with the original issue that
> gen_pool_dma_alloc_align() does not reserve the remainder of the page
> and could give it out to other allocations. We'd need a separate patch
> for that.

That can be fixed by the pcm_memory.c change in the previous patch.
Recited below.

Of course it won't cover the non-standard allocation case, but then
it's rather the responsibility of such driver.


Takashi

---
--- a/sound/core/pcm_memory.c
+++ b/sound/core/pcm_memory.c
@@ -36,6 +36,7 @@ static int do_alloc_pages(struct snd_card *card, int type, struct device *dev,
 {
 	int err;
 
+	size = PAGE_ALIGN(size)
 	if (max_alloc_per_card &&
 	    card->total_pcm_alloc_bytes + size > max_alloc_per_card)
 		return -ENOMEM;
@@ -187,7 +188,7 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry,
 				buffer->error = -ENOMEM;
 				return;
 			}
-			substream->buffer_bytes_max = size;
+			substream->buffer_bytes_max = new_dmab.bytes;
 		} else {
 			substream->buffer_bytes_max = UINT_MAX;
 		}