Re: [PATCH v1 ] ALSA: core: memalloc: add page alignment for iram
From: Lars-Peter Clausen
Date: Thu Dec 17 2020 - 06:00:11 EST
On 12/17/20 10:55 AM, Takashi Iwai wrote:
On Thu, 17 Dec 2020 10:43:45 +0100,
Lars-Peter Clausen wrote:
On 12/17/20 5:15 PM, Robin Gong wrote:
Since mmap for userspace is based on page alignment, add page alignment
for iram alloc from pool, otherwise, some good data located in the same
page of dmab->area maybe touched wrongly by userspace like pulseaudio.
I wonder, do we also have to align size to be a multiple of PAGE_SIZE
to avoid leaking unrelated data?
Hm, a good question. Basically the PCM buffer size itself shouldn't
be influenced by that (i.e. no hw-constraint or such is needed), but
the padding should be cleared indeed. I somehow left those to the
allocator side, but maybe it's safer to clear the whole buffer in
sound/core/memalloc.c commonly.
What I meant was that most of the APIs that we use to allocate memory
work on a PAGE_SIZE granularity. I.e. if you request a buffer that where
the size is not a multiple of PAGE_SIZE internally they will still
allocate a buffer that is a multiple of PAGE_SIZE and mark the unused
bytes as reserved.
But I believe that is not the case gen_pool_dma_alloc(). It will happily
allocate those extra bytes to some other allocation request.
That we need to zero out the reserved bytes even for those other APIs is
a very good additional point!
I looked at this a few years ago and I'm pretty sure that we cleared out
the allocated area, but I can't find that anymore in the current code.
Which is not so great I guess.