[PATCH v5 0/5] kdump: Allow ELF header creation in new kernel

[Michael Holzheu]

Hello Vivek,

Sorry for the late reply. It took me some time to implement the page fault
mechanism to be used for zfcpdump.

So here the 5th version of the patch set. Included are also the required
changes for s390 regarding the new mmap support.

First some answers to outstanding questions:

> Ok, zfcpdump is a problem because HSA memory region is in addition to
> regular memory address space. 
>
> Yep trying to figure out unused memory region in first kernel and mapping
> HSA to that is little ugly. But you know s390 better, so you decide
> whether you want to take that path or not.

I would prefer the solution with the arch dependent ELF header access
functions as we already discussed (see this patch set).

> How about if we introduce another function to read notes, say
> arch_read_crash_notes(). So arch_read_from_crash_header() is meant
> to get just ELF headers (ELF header and PT_LOAD, PT_NOTE type elf headers)
> and arch_read_crash_notes() gets the data as pointed by PT_NOTE elf
> header.

I added that function.

Besides of that, as said above, I implemented mmap support for zfcpdump
by adding a fault handler function to vmcore. Also I did some other minor
changes (see change log).

In this patch series I did not include the discussed ELF header swap trick
patch because with the ELF header read functions this patch currently is
not necessary.

Best Regards,
Michael

ChangeLog
=========
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/kdump/mmap: Implement remap_oldmem_pfn_range for s390

Michael Holzheu (4):
  kdump: Introduce ELF header in new memory feature
  s390/kdump: Use ELF header in new memory feature
  vmcore/mmap: Introduce remap_oldmem_pfn_range()
  s390/kdump: Use vmcore for zfcpdump

 arch/s390/Kconfig             |   3 +-
 arch/s390/include/asm/sclp.h  |   1 +
 arch/s390/kernel/crash_dump.c | 203 +++++++++++++++++++++++++++++++++---------
 drivers/s390/char/zcore.c     |   6 +-
 fs/proc/vmcore.c              | 157 +++++++++++++++++++++++++++-----
 include/linux/crash_dump.h    |   8 ++
 6 files changed, 314 insertions(+), 64 deletions(-)

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1.8.1.6