[Crash-utility] Re: [PATCH] loongarch64: fix mem section init failure

On 8/24/26 20:13, Dave Young wrote: Hi Dave, Thanks for finding this. I checked the history again. The value 28 in crash was not just an arbitrary downstream setting. LoongArch mainline has used SECTION_SIZE_BITS=29 since the initial upstream support, but there is a known issue with that value on LoongArch systems. With SECTION_SIZE_BITS=29, one memsection covers 512 MB, while the low physical address layout contains 256 MB of RAM followed by a 256 MB I/O register region. As a result, the I/O region may be treated as valid memory by the generic pfn_valid() implementation. There was already an upstream kernel patch in 2022 titled "LoongArch: Fix memsection size" which changed SECTION_SIZE_BITS from 29 to 28 to avoid accessing the I/O region during suspend/resume. Our downstream kernels have carried this change, which is why the original crash LoongArch support used 28. So I think there are actually two issues here: The mainline LoongArch kernel should probably be fixed to use SECTION_SIZE_BITS=28. crash should ideally obtain SECTION_SIZE_BITS from VMCOREINFO instead of hard-coding either 28 or 29, so that it can handle both existing mainline kernels and downstream kernels correctly. The kernel already exports NUMBER(SECTION_SIZE_BITS) in VMCOREINFO, so I think using that value when available would be more robust than simply changing the crash default from 28 to 29. I will also revisit the old kernel-side fix and see about getting it upstream. Thanks, Ming