Re: [PATCH v2] mm/cma: simplify cma_declare_contiguous_multi()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/cma: unguarded 64-bit SZ_4G comparison in
  cma_find_free_range() on 32-bit
--

commit c3ad286c7568d10ee09caebdcdc606cff727c93b
Author: Mike Rapoport (Microsoft) <rppt@kernel.org>

mm/cma: simplify cma_declare_contiguous_multi()

This commit replaces the linked-list range collection in
cma_declare_contiguous_multi() with a loop that repeatedly reserves the
largest free memblock range above 4G and then sorts the resulting ranges.

> diff --git a/mm/cma.c b/mm/cma.c
> index f61d52796f4ef..f01850d13799f 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c

[ ... ]

> @@ -524,37 +474,71 @@ static int __init __cma_declare_contiguous_nid(phys_addr_t *basep,
>  	return 0;
>  }
>  
> +/*
> + * Find the largest free range above 4G that can hold a part of a multi-range
> + * CMA area.
> + */
> +static phys_addr_t __init cma_find_free_range(phys_addr_t align,
> +		phys_addr_t size_align, int nid, phys_addr_t *basep)
> +{
> +	phys_addr_t start, end, size;
> +	phys_addr_t max = 0;
> +	u64 i;
> +
> +	for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &start, &end, NULL) {
> +		if (start < SZ_4G)
> +			continue;

[Severity: Low]
Does comparing start against SZ_4G trigger a
-Wtautological-constant-out-of-range-compare warning on 32-bit Clang W=1
builds when CONFIG_PHYS_ADDR_T_64BIT is disabled?

When CONFIG_PHYS_ADDR_T_64BIT is not set, phys_addr_t is u32 while SZ_4G
is 0x100000000ULL.  The previous code checked upper_32_bits(start) == 0,
and cma_alloc_mem() in the same file guards its SZ_4G check with #ifdef
CONFIG_PHYS_ADDR_T_64BIT.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111-cma-multi-v2-1-4e2dddb2a2d8@kernel.org?part=1