Re: RDMA Read: Local protection error

[Sagi Grimberg <sagi-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>]

>>>> When debugging is disabled, kzalloc returns page-aligned
>>>> addresses:
>>>
>>> Is it defined some where that regular kzalloc/kmalloc guaranties to
>>> return a page-aligned address as you see in your testing ? if so the
>>> debug mode should behave the same. Otherwise we can consider using any
>>> flag allocation that can force that if such exists.
>>> Let's get other people's input here.
>>
>> My understanding is that the fact that k[mz]alloc() returns a page-aligned buffer if the allocation size is > PAGE_SIZE / 2 is a side effect of the implementation and not something callers of that function should rely on. I think the only assumption k[mz]alloc() callers should rely on is that the allocated memory respects ARCH_KMALLOC_MINALIGN.
>
> I agree. mlx4_alloc_priv_pages() is carefully designed to
> correct the alignment of the buffer, so it already assumes
> that it is not getting a page-aligned buffer.
>
> The alignment isn't the problem here, though. It's that
> the buffer contains a page-boundary. That is guaranteed
> to be the case for HCAs that support more than 512
> sges, so that will have to be addressed (at least in
> mlx5).

rrr...

I think we should make the pages allocations dma coherent
in order to fix that...

Nice catch Chunk.
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