[PATCH v5 1/2] x86/crash: reserve elfcorehdr for CONFIG_NR_CPUS, not CONFIG_NR_CPUS_DEFAULT

[Sourabh Jain]

Hello,

The below patch overrides the changes introduce here:
https://lore.kernel.org/all/20260826092541.3905933-13-ruanjinjie@huawei.com/

Can you please review the above patch instead?

- Sourabh Jain

On 01/09/26 12:40, Ionut Nechita (Wind River) wrote:
> From: Ionut Nechita <ionut.nechita at windriver.com>
>
> NR_CPUS_DEFAULT is purely a Kconfig thing.  Its entire purpose in life is
> to start NR_CPUS at a sane value.  There is precisely one (buggy)
> reference to it outside of Kconfig in the whole kernel: the x86 crash
> code.
>
> That code undersizes the elfcorehdr reservation whenever NR_CPUS exceeds
> NR_CPUS_DEFAULT, because the header carries one phdr per possible CPU and
> num_possible_cpus() is bounded by NR_CPUS.  kexec_file_load(2) then fails
> with -EINVAL from sanity_check_segment_list(), and kexec_load(2) silently
> truncates the elfcorehdr, which surfaces later as a bad or unusable dump.
>
> Size the elfcorehdr reservation with NR_CPUS instead.
>
> Fixes: ea53ad9cf73b ("x86/crash: add x86 crash hotplug support")
> Assisted-by: LLM
> Signed-off-by: Ionut Nechita <ionut.nechita at windriver.com>
> Reviewed-by: Jinjie Ruan <ruanjinjie at huawei.com>
> Reviewed-by: Bradley Morgan <brads at mainlining.org>
> Reviewed-by: Sourabh Jain <sourabhjain at linux.ibm.com>
> Acked-by: Baoquan He <baoquan.he at linux.dev>
> ---
>   arch/x86/kernel/crash.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index e681ec9cf1dc..e6f23933a6df 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -369,9 +369,9 @@ int crash_load_segments(struct kimage *image)
>   	 * maximum CPUs and maximum memory ranges.
>   	 */
>   	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> -		pnum = 2 + CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES;
> +		pnum = 2 + CONFIG_NR_CPUS + CONFIG_CRASH_MAX_MEMORY_RANGES;
>   	else
> -		pnum += 2 + CONFIG_NR_CPUS_DEFAULT;
> +		pnum += 2 + CONFIG_NR_CPUS;
>   
>   	if (pnum < (unsigned long)PN_XNUM) {
>   		kbuf.memsz = pnum * sizeof(Elf64_Phdr);
> @@ -430,7 +430,7 @@ unsigned int arch_crash_get_elfcorehdr_size(void)
>   	unsigned int sz;
>   
>   	/* kernel_map, VMCOREINFO and maximum CPUs */
> -	sz = 2 + CONFIG_NR_CPUS_DEFAULT;
> +	sz = 2 + CONFIG_NR_CPUS;
>   	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>   		sz += CONFIG_CRASH_MAX_MEMORY_RANGES;
>   	sz *= sizeof(Elf64_Phdr);
>
> base-commit: 89c07d98716a13454ec3fd9f97689e812cc71bd4