[PATCH v2 0/3] kdump: Allow ELF header creation in new kernel

From: Michael Holzheu
Date: Wed May 22 2013 - 13:59:21 EST

Hello Vivek,

Here the 2nd version of the patch set. We tried to implement the
function using the arch_get/free_crash_header() weak function as
you suggested. We kept the ELFCORE_ADDR_NEWMEM define so that
is_kdump_kernel() also works for our case.

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 arch function call for kdump

arch/s390/Kconfig | 3 +-
arch/s390/include/asm/sclp.h | 1 +
arch/s390/kernel/crash_dump.c | 126 +++++++++++++++++++++++++++++++-----------
drivers/s390/char/zcore.c | 6 +-
fs/proc/vmcore.c | 80 +++++++++++++++++++++------
include/linux/crash_dump.h | 3 +
6 files changed, 164 insertions(+), 55 deletions(-)


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