[PATCH 2/2] makedumpfile: Use max_pfn from mem_map array

[Michael Holzheu]

There are dump mechansims like s390 stand-alond dump or KVM virsh dump
that write the physical memory of a machine and are not aware of the
dumped operating system. For those dump mechanisms it can happen
that for the Linux kernel of the dumped system the "mem=" kernel
parameter has been specified. In this case max_mapnr that makedumpfile
gets from the ELF header can be bigger than the maximum page frame number
used by the dumped Linux kernel.

With this patch makedumpfile gets the maximum page frame number from
the mem_map array and adjusts info->max_mapnr if this value is smaller
than the value calculated from the ELF header.

Signed-off-by: Michael Holzheu <holzheu at linux.vnet.ibm.com>
---
 makedumpfile.c |   14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -2829,7 +2829,8 @@ get_mem_map_without_mm(void)
 int
 get_mem_map(void)
 {
-	int ret;
+	unsigned long max_pfn = 0;
+	int ret, i;
 
 	switch (get_mem_type()) {
 	case SPARSEMEM:
@@ -2861,6 +2862,17 @@ get_mem_map(void)
 		ret = FALSE;
 		break;
 	}
+	/*
+	 * Adjust "max_mapnr" for the case that Linux uses less memory
+	 * than is dumped. For example when "mem=" has been used for the
+	 * dumped system.
+	 */
+	for (i = 0; i < info->num_mem_map; i++) {
+		if (info->mem_map_data[i].mem_map == NOT_MEMMAP_ADDR)
+			continue;
+		max_pfn = MAX(max_pfn, info->mem_map_data[i].pfn_end);
+	}
+	info->max_mapnr = MIN(info->max_mapnr, max_pfn);
 	return ret;
 }