Can't load bzImage crashkernel on xen system with 32 bit kernel

[Anthony Wright]

Hi Chao,

Thanks for looking at this.

On 10/07/2014 08:47, WANG Chao wrote:
> Hi, Anthony
>
> On 07/08/14 at 11:34am, Anthony Wright wrote:
>> After successfully modifying kexec-tools to get it to load a crashkernel
>> on a standard 32 bit linux 3.10.17 kernel, I tried to get it to load the
>> same crashkernel on the same 32 bit linux kernel running under xen
>> 4.4.0, but get the error "Cannot load <kernel-path>".
>>
>> I've patched the code to include some diagnostics, and the problem is
>> caused by add_memmap() reporting that it's been called with overlapping
>> memory.
>>
>> It's called twice, the first time it's called with:
>> 	address: 0x00000000
>> 	size:    0x0009f800
>> 	type:    0
>>
>> This comes from info->backup_src_*
>>
>> The second time it is passed
>> 	address: 0x00000000
>> 	size:    0x00000000
>> 	type:    0
>>
>> This is derived from the crash_reserved_mem[] array, which has one
>> element with the values:
>> 	start: 0x0000000000000000 (16 0's)
>> 	end:   0xffffffffffffffff (16 f's)
> Why it looks like that? crashkernel memory region shouldn't be that
> extreme.
Is it something to do with xen 4.4.0? The xen hypervisor is 64 bit, but
the Dom0 linux kernel is 32 bit. I realise this is a bit of a strange
combination, but we run this way for historical reasons.
> Maybe there's something wrong when it retrieves crashkernel reserved
> region. How you does your /proc/iomem look like?
>
> Turn on debug option (-d) would be helpful too.
I've attached a copy of /proc/iomem and the output of kexec with the -d
flag.
>> The problem isn't caused by the zero size because the maths in
>> add_memmap, uses size to calculate end which overflows back again, and
>> (partially) cancels out the error. The problem is caused by the two
>> memory blocks being based at 0x0, causing the blocks to overlap.
> The overflow issue should be easy to fix once we figure out why the
> crash_reserved_mem[] has a element like that.
>
> Thanks
> WANG Chao
thanks,

Anthony.
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00000000-00000fff : reserved
00001000-0009efff : System RAM
0009f000-0009f7ff : RAM buffer
0009f800-000fffff : reserved
  000a0000-000bffff : PCI Bus 0000:00
  000c0000-000cebff : Video ROM
  000d0000-000dffff : PCI Bus 0000:00
  000f0000-000fffff : System ROM
00100000-cff9ffff : System RAM
  01000000-015897cd : Kernel code
  015897ce-0182debf : Kernel data
  018e6000-019bbfff : Kernel bss
  18000000-1fffffff : Crash kernel
cffa0000-cffaffff : ACPI Tables
cffb0000-cffdffff : ACPI Non-volatile Storage
cffe0000-cfffffff : reserved
d0000000-dfffffff : PCI Bus 0000:00
  d0000000-dfffffff : PCI Bus 0000:01
    d0000000-dfffffff : 0000:01:05.0
e0000000-efffffff : PCI MMCONFIG 0000 [bus 00-ff]
  e0000000-efffffff : pnp 00:0c
f0000000-febfffff : PCI Bus 0000:00
  fdf00000-fdffffff : PCI Bus 0000:03
    fdff8000-fdffbfff : 0000:03:00.0
      fdff8000-fdffbfff : r8169
    fdfff000-fdffffff : 0000:03:00.0
      fdfff000-fdffffff : r8169
  fe7f4000-fe7f7fff : 0000:00:14.2
  fe7fa000-fe7fafff : 0000:00:14.5
    fe7fa000-fe7fafff : ohci_hcd
  fe7fb000-fe7fbfff : 0000:00:13.1
    fe7fb000-fe7fbfff : ohci_hcd
  fe7fc000-fe7fcfff : 0000:00:13.0
    fe7fc000-fe7fcfff : ohci_hcd
  fe7fd000-fe7fdfff : 0000:00:12.1
    fe7fd000-fe7fdfff : ohci_hcd
  fe7fe000-fe7fefff : 0000:00:12.0
    fe7fe000-fe7fefff : ohci_hcd
  fe7ff400-fe7ff4ff : 0000:00:13.2
    fe7ff400-fe7ff4ff : ehci_hcd
  fe7ff800-fe7ff8ff : 0000:00:12.2
    fe7ff800-fe7ff8ff : ehci_hcd
  fe7ffc00-fe7fffff : 0000:00:11.0
    fe7ffc00-fe7fffff : ahci
  fe800000-fe9fffff : PCI Bus 0000:01
    fe800000-fe8fffff : 0000:01:05.0
    fe9f0000-fe9fffff : 0000:01:05.0
  fea00000-feafffff : PCI Bus 0000:02
    feaff800-feafffff : 0000:02:00.0
      feaff800-feafffff : firewire_ohci
  feb00000-febfffff : PCI Bus 0000:03
    febe0000-febfffff : 0000:03:00.0
fec00000-fec003ff : IOAPIC 0
fec10000-fec1001f : pnp 00:08
fee00000-feefffff : reserved
  fee00000-fee00fff : Local APIC
    fee00000-fee00fff : pnp 00:07
ffb80000-ffbfffff : pnp 00:08
fff00000-ffffffff : reserved
100000000-21fffffff : System RAM
fd00000000-ffffffffff : reserved
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