Re: [PATCH v5 17/17] arm64: crash: Add crash hotplug support

[Jinjie Ruan]

在 2026/9/18 18:36, sashiko-bot@xxxxxxxxxx 写道:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] kexec: arch_crash_get_elfcorehdr_size() exports undersized buffer when MEMORY_HOTPLUG is disabled
> --
> 
> commit fd293f9cfd1a12554d9352f4ad58fc9f85721fa3
> Author: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> arm64: crash: Add crash hotplug support
> 
> This commit introduces kernel mechanisms to update only the elfcorehdr
> on memory hotplug events for arm64. It adds ARCH_SUPPORTS_CRASH_HOTPLUG 
> and implements arch-specific functions to handle memory hotplug, avoiding
> full kdump image reloads from userspace.
> 
> Link: https://lore.kernel.org/all/20240529133446.28446-1-Jonathan.Cameron@xxxxxxxxxx/
> 
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index b5a51b0ef9440..96de2660b1cbb 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -1720,6 +1720,9 @@ config ARCH_DEFAULT_CRASH_DUMP
>>  config ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
>>  	def_bool CRASH_RESERVE
>>  
>> +config ARCH_SUPPORTS_CRASH_HOTPLUG
>> +	def_bool y
>> +
> 
> [Severity: High]
> Does unconditionally enabling ARCH_SUPPORTS_CRASH_HOTPLUG here expose an
> undersized buffer to userspace when CONFIG_MEMORY_HOTPLUG is disabled?
> 
> Since CONFIG_HOTPLUG_CPU natively selects CONFIG_CRASH_HOTPLUG on
> architectures that support it, having this default to 'y' allows
> CRASH_HOTPLUG to be active even without MEMORY_HOTPLUG. This leads to the
> size calculation issue below.
> 
> [ ... ]
>> diff --git a/arch/arm64/kernel/crash.c b/arch/arm64/kernel/crash.c
>> new file mode 100644
>> index 0000000000000..08dc9b952498e
>> --- /dev/null
>> +++ b/arch/arm64/kernel/crash.c
> [ ... ]
>> +unsigned int arch_crash_get_elfcorehdr_size(void)
>> +{
>> +	unsigned long phdr_cnt;
>> +
>> +	/* A program header for possible CPUs, vmcoreinfo and kernel_map */
>> +	phdr_cnt = 2 + num_possible_cpus();
>> +	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> +		phdr_cnt += CONFIG_CRASH_MAX_MEMORY_RANGES;
>> +
> 
> [Severity: High]
> Is this calculation missing the static memory ranges when
> CONFIG_MEMORY_HOTPLUG is disabled?
> 
> If compiled with CONFIG_HOTPLUG_CPU=y (which natively selects
> CONFIG_CRASH_HOTPLUG) and CONFIG_MEMORY_HOTPLUG=n, phdr_cnt is computed as
> exactly 2 + num_possible_cpus(). This does not account for the mandatory
> memblock ranges from arch_get_system_nr_ranges(). 

Will fix it in v6.

> 
> Unlike x86 or powerpc which might survive this due to heavily padded
> CONFIG_NR_CPUS_DEFAULT values, arm64's precise num_possible_cpus() leaves
> zero headroom. As a result, the exported maximum elfcorehdr size is strictly
> smaller than the required size to hold static memory ranges, and any attempt
> to arm kdump (kexec -p) will fail because kexec-tools cannot load the crash
> kernel into the undersized segment.
> 

-- 
Best regards,
Jinjie