[PATCH 0/3] kdump: Allow ELF header creation in new kernel

Michael Holzheu holzheu at linux.vnet.ibm.com
Thu May 23 14:56:58 EDT 2013

Hello Vivek,

Here, as discussed, the 3nd version of the patch set.

v2 => v3)
- Make read_from_crash_header() only read from kernel
- Move read_from_crash_header() to weak function arch_read_from_crash_header()
- Implement read_from_crash_header() strong function for s390
- Set elfcorehdr_addr to address of new ELF header

v1 => v2)

- Rebase 3.10-rc2 + vmcore mmap patches
- Introduced arch_get/free_crash_header() and ELFCORE_ADDR_NEWMEM

Feature Description
For s390 we want to use /proc/vmcore for our SCSI stand-alone
dump (zfcpdump). We have support where the first HSA_SIZE bytes are
saved into a hypervisor owned memory area (HSA) before the kdump
kernel is booted. When the kdump kernel starts, it is restricted
to use only HSA_SIZE bytes.

The advantages of this mechanism are:

* No crashkernel memory has to be defined in the old kernel.
* Early boot problems (before kexec_load has been done) can be dumped 
* Non-Linux systems can be dumped.

We modify the s390 copy_oldmem_page() function to read from the HSA memory
if memory below HSA_SIZE bytes is requested.

Since we cannot use the kexec tool to load the kernel in this scenario,
we have to build the ELF header in the 2nd (kdump/new) kernel.

So with the following patch set we would like to introduce the new
function that the ELF header for /proc/vmcore can be created in the 2nd
kernel memory.

The following steps are done during zfcpdump execution:

1.  Production system crashes
2.  User boots a SCSI disk that has been prepared with the zfcpdump tool
3.  Hypervisor saves CPU state of boot CPU and HSA_SIZE bytes of memory into HSA
4.  Boot loader loads kernel into low memory area
5.  Kernel boots and uses only HSA_SIZE bytes of memory
6.  Kernel saves registers of non-boot CPUs
7.  Kernel does memory detection for dump memory map
8.  Kernel creates ELF header for /proc/vmcore
9.  /proc/vmcore uses this header for initialization
10. The zfcpdump user space reads /proc/vmcore to write dump to SCSI disk
    - copy_oldmem_page() copies from HSA for memory below HSA_SIZE
    - copy_oldmem_page() copies from real memory for memory above HSA_SIZE

Jan Willeke (1):
  s390/kdump: Use vmcore for zfcpdump

Michael Holzheu (2):
  kdump: Introduce ELF header in new memory feature
  s390/kdump: Use ELF header in new memory feature

 arch/s390/Kconfig             |   3 +-
 arch/s390/include/asm/sclp.h  |   1 +
 arch/s390/kernel/crash_dump.c | 138 +++++++++++++++++++++++++++++++-----------
 drivers/s390/char/zcore.c     |   6 +-
 fs/proc/vmcore.c              |  65 ++++++++++++++------
 include/linux/crash_dump.h    |   4 ++
 6 files changed, 161 insertions(+), 56 deletions(-)


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