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

[Dave Anderson]

----- Original Message -----
> 
> 
> ----- 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, ...

Actually that won't suffice, because the POST_GDB init call is done
before vm_init().  I'll add a new POST_VM case label to the s390x_init()
switch statement, and move the set_s390x_max_physmem_bits() call there.

Dave