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.
So I believe it's safer to add an extra memset() like my test patch.
Takashi