[PATCH v8 0/6] kdump: Allow ELF header creation in new kernel

[Michael Holzheu]

Hello Andrew,

Here the new kdump patch series as discussed with Vivek and Hatayama
during the last months.

I adjusted the code to v3.11-rc2 where the following patches have been
integrated:

https://git.kernel.org/cgit/linux/kernel/git/s390/linux.git/commit/?h=features&id=5a74953ff56aa870d6913ef4d81934f5c620c59d
https://git.kernel.org/cgit/linux/kernel/git/s390/linux.git/commit/?h=features&id=191a2fa0a8d2bbb64c98f9b1976fcb37ee5eae6b 

Vivek has accepted the patch series. So would you integrate it into 3.12?

Best Regards,
Michael

ChangeLog
=========
v7 => v8)

- Rebase to v3.11-rc2
- Add patch 5/6: vmcore: Enable /proc/vmcore mmap for s390

v6 => v7)

- Rebase to v3.11-rc1
- Return VM_FAULT_SIGBUS in fault handler for non s390
- Use __va() for buffer in fault handler

v5 => v6)

- Set elfcorehdr_addr to ELFCORE_ADDR_ERR after elfcorehdr_free()
- Fix OLDMEM_SIZE/ZFCPDUMP_HSA_SIZE confusion
- Remove return VM_FAULT_MAJOR/MINOR
- Use find_or_create_page() in mmap_vmcore_fault()
- Use kfree instead of vfree in elfcorehdr_free()

v4 => v5)

- Add weak function elfcorehdr_read_notes() to read ELF notes
- Rename weak functions for ELF header access and use "vmcorehdr_" prefix
- Generic vmcore code calls elfcorehdr_alloc() if elfcorehdr= is not specified
- Add vmcore fault handler for mmap of non-resident memory regions
- Add weak function remap_oldmem_pfn_range() to be used by zfcpdump for mmap

v3 => v4)

- Rebase to 3.10-rc2 + vmcore mmap patches v8

v2 => v3)

- Get rid of ELFCORE_ADDR_NEWMEM
- 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/vmcore: Implement remap_oldmem_pfn_range for s390

Michael Holzheu (5):
  vmcore: Introduce ELF header in new memory feature
  s390/vmcore: Use ELF header in new memory feature
  vmcore: Introduce remap_oldmem_pfn_range()
  vmcore: Enable /proc/vmcore mmap for s390
  s390/vmcore: Use vmcore for zfcpdump

 arch/s390/Kconfig             |   3 +-
 arch/s390/include/asm/sclp.h  |   1 +
 arch/s390/kernel/crash_dump.c | 219 ++++++++++++++++++++++++++++++++++--------
 drivers/s390/char/zcore.c     |   6 +-
 fs/proc/vmcore.c              | 154 +++++++++++++++++++++++++----
 include/linux/crash_dump.h    |   9 ++
 6 files changed, 329 insertions(+), 63 deletions(-)

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1.8.2.3