RE: [PATCH v4 02/24] powerpc/pseries: Fix alignment of PLPKS structures and buffers

David Laight
2023-01-27T09:05:45Z

From: Andrew Donnellan
> Sent: 27 January 2023 03:21
>
> On Thu, 2023-01-26 at 17:31 +0000, David Laight wrote:
> > Changing the size to kzalloc() doesn't help.
> > The alignment depends on the allocator and is only required to have
> > a relatively small alignment (ARCH_MINALIGN?) regardless of the size.
> >
> > IIRC one of the allocators adds a small header to every item.
> > It won't return 16 byte aligned items at all.
>
> I'm relying on the behaviour described in Documentation/core-
> api/memory-allocation.rst:
>
> The address of a chunk allocated with kmalloc is aligned to at
> least ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of
> two, the alignment is also guaranteed to be at least the respective
> size.
>
> Is this wrong?

The alignment for power of two doesn't match what I've inferred
from reading comments on other patches.

It is true for dma_malloc_coherent() - that does guarantee that a
16k allocate will be aligned on a 16k physical address boundary.

David

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