[PATCH] kho: Skip zero-sized bootmem areas

[sashiko-bot at kernel.org]

> The lowmem and the global bootmem area are reserved unconditionally,
> while the per-node loop below already skips nodes whose size works out
> to 0. Either can legitimately be 0: the global size is the scaled total
> minus the lowmem one, so it is 0 whenever all measured reservations fit
> below ARCH_LOW_ADDRESS_LIMIT.
> 
> Reserving 0 bytes still succeeds, so an area covering nothing gets
> recorded with a valid address. That is not neutral:
> kho_bootmem_overlap() reports an overlap for any request straddling
> that address, and memblock_alloc_hugetlb() aligns a request to its page
> size, so a 1G hugetlb allocation retries a free candidate on account of
> an area that holds nothing.
> 
> A machine whose memory all starts at or above ARCH_LOW_ADDRESS_LIMIT
> hits the other side of the same code: the lowmem size is 0, the range
> below the limit is empty, the allocation fails and KHO is disabled
> although no lowmem area was needed.
> 
> Skip a zero-sized area instead, as the per-node loop does. The
> descriptor count stays consistent, as kho_populate() derives it from
> the segment length that kho_fill_kimage() serialises.
> 
> Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
> Signed-off-by: Chen Pei <cp0613 at linux.alibaba.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261026131851.9942-1-cp0613@linux.alibaba.com?part=1