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

[Mahesh J Salgaonkar]

Hi Tachibana,

As part of the s390 patch to add support for > 4TB system memory (present in
linux-next tree), the newer s390 kernel will bump the MAX_PHYSMEM_BITS from
42 to 46. Once that patch makes into umpstream kernel, this change will need
to go into makedumpfile.  For now, I am posting this patch for a review.

Reference: http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commit;h=8980036860565a6d2a4f95bb097927e832fa3d1a

Thanks,
-Mahesh.


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 auto-detects 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>
---
 arch/s390x.c   |   27 ++++++++++++++++++++++++++-
 makedumpfile.h |    3 ++-
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/s390x.c b/arch/s390x.c
index 9237eaa..c73220a 100644
--- a/arch/s390x.c
+++ b/arch/s390x.c
@@ -60,6 +60,28 @@
 #define pte_offset(x)		(pte_index(x) * sizeof(unsigned long))
 
 int
+set_s390x_max_physmem_bits(void)
+{
+	long array_len = ARRAY_LENGTH(mem_section);
+	/*
+	 * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
+	 * newer kernels uses 46 bits.
+	 */
+
+	info->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;
+
+	info->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;
+}
+
+int
 get_machdep_info_s390x(void)
 {
 	unsigned long vmalloc_start;
@@ -70,7 +92,10 @@ get_machdep_info_s390x(void)
 		flag_ignore_r_char = 1;
 
 	info->section_size_bits = _SECTION_SIZE_BITS;
-	info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
+	if (!set_s390x_max_physmem_bits()) {
+		ERRMSG("Can't detect max_physmem_bits.\n");
+		return FALSE;
+	}
 	info->page_offset = __PAGE_OFFSET;
 
 	if (SYMBOL(_stext) == NOT_FOUND_SYMBOL) {
diff --git a/makedumpfile.h b/makedumpfile.h
index b3de521..a95d132 100644
--- a/makedumpfile.h
+++ b/makedumpfile.h
@@ -531,7 +531,8 @@ do { \
 #define KERNELBASE		(0)
 #define KVBASE			KERNELBASE
 #define _SECTION_SIZE_BITS	(28)
-#define _MAX_PHYSMEM_BITS	(42)
+#define _MAX_PHYSMEM_BITS_OLD	(42)
+#define _MAX_PHYSMEM_BITS_NEW	(46)
 
 /* Bits in the segment/region table address-space-control-element */
 #define _ASCE_TYPE_MASK		0x0c