linux-kernel - Re: [PATCH 1/2] mm/cma: drop incorrect alignment check in cma_init_reserved

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Date: Thu, 4 Apr 2024 13:15:49 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Frank van der Linden <fvdl@...gle.com>
Cc: linux-mm@...ck.org, muchun.song@...ux.dev, linux-kernel@...r.kernel.org,
 Marek Szyprowski <m.szyprowski@...sung.com>, David Hildenbrand
 <david@...hat.com>
Subject: Re: [PATCH 1/2] mm/cma: drop incorrect alignment check in
 cma_init_reserved_mem

On Thu,  4 Apr 2024 16:25:14 +0000 Frank van der Linden <fvdl@...gle.com> wrote:

> cma_init_reserved_mem uses IS_ALIGNED to check if the size
> represented by one bit in the cma allocation bitmask is
> aligned with CMA_MIN_ALIGNMENT_BYTES (pageblock size).
> 
> However, this is too strict, as this will fail if
> order_per_bit > pageblock_order, which is a valid configuration.
> 
> We could check IS_ALIGNED both ways, but since both numbers are
> powers of two, no check is needed at all.

What are the userspace visible effects of this bug?