Messages in this thread | | | Subject | Re: [PATCH v1 ] ALSA: core: memalloc: add page alignment for iram | From | Lars-Peter Clausen <> | Date | Thu, 17 Dec 2020 11:59:23 +0100 |
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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.
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