[Crash-utility] [PATCH] Crash-Utility: s390x: Auto-detect the correct MAX_PHYSMEM_BITS used in vmcore being analyzed.

[Dave Anderson]

----- Original Message -----
> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> 
> So far s390x kernel was using 42 bits for MAX_PHYSMEM_BITS that use to
> support maximum of 4TB of memory. In order to support bigger systems,
> the newer s390x kernel will now use 46 bits for MAX_PHYSMEM_BITS to support
> maximum of 64TB of memory.
> 
> This patch enhances crash utility to auto-detect the correct value to use
> for MAX_PHYSMEM_BITS by examining the mem_section array size from the vmcore
> being analyzed.
> 
> Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> ---
>  defs.h  |    3 ++-
>  s390x.c |   26 +++++++++++++++++++++++++-
>  2 files changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/defs.h b/defs.h
> index 381e8c2..eb992d1 100755
> --- a/defs.h
> +++ b/defs.h
> @@ -2954,7 +2954,8 @@ struct efi_memory_desc_t {
>  #define TIF_SIGPENDING (2)
>  
>  #define _SECTION_SIZE_BITS	28
> -#define _MAX_PHYSMEM_BITS	42
> +#define _MAX_PHYSMEM_BITS_OLD	42
> +#define _MAX_PHYSMEM_BITS_NEW	46
>  
>  #endif  /* S390X */
>  
> diff --git a/s390x.c b/s390x.c
> index 22e29a9..53bf272 100755
> --- a/s390x.c
> +++ b/s390x.c
> @@ -282,6 +282,29 @@ static void s390x_process_elf_notes(void
> *note_ptr, unsigned long size_note)
>  	}
>  }
>  
> +static int
> +set_s390x_max_physmem_bits(void)
> +{
> +	int array_len = get_array_length("mem_section", NULL, 0);
> +	/*
> +	 * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
> +	 * newer kernels uses 46 bits.
> +	 */
> +
> +	STRUCT_SIZE_INIT(mem_section, "mem_section");
> +	machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_OLD;
> +	if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> +		|| (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> +		return TRUE;
> +
> +	machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_NEW;
> +	if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> +		|| (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> +		return TRUE;
> +
> +	return FALSE;
> +}
> +
>  /*
>   *  Do all necessary machine-specific setup here.  This is called several
>   *  times during initialization.
> @@ -350,7 +373,8 @@ s390x_init(int when)
>  		if (!machdep->hz)
>  			machdep->hz = HZ;
>  		machdep->section_size_bits = _SECTION_SIZE_BITS;
> -		machdep->max_physmem_bits = _MAX_PHYSMEM_BITS;
> +		if (!set_s390x_max_physmem_bits())
> +			error(FATAL, "Can't detect max_physmem_bits.");
>  		s390x_offsets_init();
>  		break;

This would seem to be a little extreme.  If by chance CONFIG_SPARSEMEM 
is not configured, or for that matter, in old pre-sparsemem kernels, 
"mem_section" doesn't even exist as a symbol.  So there should be an 
IS_SPARSEMEM() qualifier to prevent the FATAL session-ending error. 

I'm waiting for an s390x reservation as we speak, and I'll change 
(and test) the patch to do something like:

               if (IS_SPARSEMEM() && !set_s390x_max_physmem_bits())
                       error(FATAL, ...

Dave