Subject: Re: [PATCH v2 2/3] vmcore: allow fadump to export vmcore even if is_kdump_kernel() is false

From: Michael Ellerman <[email-masked]>
Date: Mon, 11 Sep 2023 17:13:08 +1000

Hari Bathini <[email-masked]> writes:
> Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
> While elfcorehdr_addr is set for kexec based kernel dump mechanism,
> alternate dump capturing methods like fadump [1] also set it to export
> the vmcore. Since, is_kdump_kernel() is used to restrict resources in
> crash dump capture kernel and such restrictions are not desirable for
> fadump, allow is_kdump_kernel() to be defined differently for fadump
> case. With that change, include is_fadump_active() check in functions
> is_vmcore_usable() & vmcore_unusable() to be able to export vmcore for
> fadump case too.
...
> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> index 0f3a656293b0..de8a9fabfb6f 100644
> --- a/include/linux/crash_dump.h
> +++ b/include/linux/crash_dump.h
> @@ -50,6 +50,7 @@ void vmcore_cleanup(void);
>  #define vmcore_elf64_check_arch(x) (elf_check_arch(x) || vmcore_elf_check_arch_cross(x))
>  #endif
>  
> +#ifndef is_kdump_kernel
>  /*
>   * is_kdump_kernel() checks whether this kernel is booting after a panic of
>   * previous kernel or not. This is determined by checking if previous kernel
> @@ -64,6 +65,19 @@ static inline bool is_kdump_kernel(void)
>  {
>  	return elfcorehdr_addr != ELFCORE_ADDR_MAX;
>  }
> +#endif
> +
> +#ifndef is_fadump_active
> +/*
> + * If f/w assisted dump capturing mechanism (fadump), instead of kexec based
> + * dump capturing mechanism (kdump) is exporting the vmcore, then this function
> + * will be defined in arch specific code to return true, when appropriate.
> + */
> +static inline bool is_fadump_active(void)
> +{
> +	return false;
> +}
> +#endif
>  
>  /* is_vmcore_usable() checks if the kernel is booting after a panic and
>   * the vmcore region is usable.
> @@ -75,7 +89,8 @@ static inline bool is_kdump_kernel(void)
>  
>  static inline int is_vmcore_usable(void)
>  {
> -	return is_kdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
> +	return (is_kdump_kernel() || is_fadump_active())
> +		&& elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
>  }
>  
>  /* vmcore_unusable() marks the vmcore as unusable,
> @@ -84,7 +99,7 @@ static inline int is_vmcore_usable(void)
>  
>  static inline void vmcore_unusable(void)
>  {
> -	if (is_kdump_kernel())
> +	if (is_kdump_kernel() || is_fadump_active())
>  		elfcorehdr_addr = ELFCORE_ADDR_ERR;
>  }

I think it would be cleaner to decouple is_vmcore_usable() and
vmcore_usable() from is_kdump_kernel().

ie, make them operate solely based on the value of elforehdr_addr:

static inline int is_vmcore_usable(void)
{
	elfcorehdr_addr != ELFCORE_ADDR_ERR && \
		elfcorehdr_addr != ELFCORE_ADDR_MAX;
}

static inline void vmcore_unusable(void)
{
	elfcorehdr_addr = ELFCORE_ADDR_ERR;
}

Then all we need on powerpc is a way to override is_kdump_kernel().

cheers