makedumpfile: get_max_mapnr() from ELF header problem

[Michael Holzheu]

Hello Atsushi,

On s390 we have the following little problem:

We use hypervisor or stand-alone dump tools to create Linux system
dumps. These tools do not know the kernel parameter line and dump the
full physical memory.

We use makedumpfile to filter those dumps.

If a Linux system has specified the "mem=" parameter, the dump tools
still dump the whole phypsical memory.

Unfortunately in "get_max_mapnr()" makedumpfile uses the ELF header to
get the maxmimum page frame number. Since this is not the correct value
in our case makedumpfile fails to filter the dump.

We get the following error on s390 with makedumpfile version 1.5.3:

makedumpfile -c -d 31 vmcore dump.kdump
cyclic buffer size has been changed: 22156083 => 22156032
Excluding unnecessary pages        : [ 21 %] vtop_s390x: Address too big for the number of page table levels.
readmem: Can't convert a virtual address(8000180104670) to physical address.
readmem: type_addr: 0, addr:8000180104670, size:32768
__exclude_unnecessary_pages: Can't read the buffer of struct page.
Excluding unnecessary pages        : [ 23 %] vtop_s390x: Address too big for the number of page table levels. readmem: Can't convert a
virtual address(8000180104670) to physical address. readmem: type_addr:
0, addr:8000180104670, size:327681.5.5 __exclude_unnecessary_pages: 
Can't read the buffer of struct page.

Since version 1.5.4 makedumpfile seems to loop in __exclude_unnecessary_pages().

We thought about several ways to fix this problem but have not found a
good solution up to now.

Do you have an idea how we could fix that?

Best Regards,
Michael