Re: slub - extended kmalloc redzone and dma alignment

[Vlastimil Babka <vbabka@suse.cz>]

On 4/8/25 5:07 PM, Catalin Marinas wrote:

> Assuming I got kmalloc redzoning right, I think there's still a
> potential issue. Let's say we have a system with 128-byte DMA alignment
> required (the largest cache line size). We do a kmalloc(104) and
> kmalloc_size_roundup() returns 128, so all seems good to the DMA code.
> However, kmalloc() redzones from 104 to 128 as it tracks the original
> size. The DMA bouncing doesn't spot it since the
> kmalloc_size_roundup(104) is aligned to 128.

Note that kmalloc_size_roundup() is supposed to be used *before*
kmalloc(), such as dma_resv_list_alloc() does. Then there's no issue as
no redzoning would not be done between 104 and 128, there would be only
the additional redzone at 128+.