On 12/17/20 12:06 PM, Takashi Iwai wrote:
On Thu, 17 Dec 2020 11:59:23 +0100,
Lars-Peter Clausen wrote:
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.
IIRC, we used GFP_ZERO in the past for the normal page allocations,
but this was dropped as it's no longer supported or so.
Also, we clear out the PCM buffer in hw_params call, but this is for
the requested size, not the actual allocated size, hence the padding
bytes will remain uncleared.
Ah! That memset() in hw_params is new.
So I believe it's safer to add an extra memset() like my test patch.
Yea, we definitely want that.
Do we care about leaking audio samples from a previous application. I.e.
application 'A' allocates a buffer plays back some data and then closes
the device again. Application 'B' then opens the same audio devices
allocates a slightly smaller buffer, so that it still uses the same
number of pages. The buffer from the previous allocation get reused, but
the remainder of the last page wont get cleared in hw_params().
