Re: [Crash-utility] [PATCH] Crash-Utility: s390x: Auto-detect the correct MAX_PHYSMEM_BITS used in vmcore being analyzed.
----- Original Message -----
----- Original Message -----
> From: Mahesh Salgaonkar <mahesh(a)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(a)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