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

[Mahesh J Salgaonkar]

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;