makedumpfile: get_max_mapnr() from ELF header problem

[Atsushi Kumagai]

>(2014/02/28 21:41), Michael Holzheu wrote:
>> Hello Atsushi,
>>
>> On s390 we have the following little problem:
>>
>> We use hypervisor or stand-alone dump tools to create Linux system
>> dumps. These tools do not know the kernel parameter line and dump the
>> full physical memory.
>>
>> We use makedumpfile to filter those dumps.
>>
>> If a Linux system has specified the "mem=" parameter, the dump tools
>> still dump the whole phypsical memory.
>>
>> Unfortunately in "get_max_mapnr()" makedumpfile uses the ELF header to
>> get the maxmimum page frame number. Since this is not the correct value
>> in our case makedumpfile fails to filter the dump.
>>
>> We get the following error on s390 with makedumpfile version 1.5.3:
>>
>> makedumpfile -c -d 31 vmcore dump.kdump
>> cyclic buffer size has been changed: 22156083 => 22156032
>> Excluding unnecessary pages        : [ 21 %] vtop_s390x: Address too big for the number of page table levels.
>> readmem: Can't convert a virtual address(8000180104670) to physical address.
>> readmem: type_addr: 0, addr:8000180104670, size:32768
>> __exclude_unnecessary_pages: Can't read the buffer of struct page.
>> Excluding unnecessary pages        : [ 23 %] vtop_s390x: Address too big for the number of page table levels. readmem:
>Can't convert a
>> virtual address(8000180104670) to physical address. readmem: type_addr:
>> 0, addr:8000180104670, size:327681.5.5 __exclude_unnecessary_pages:
>> Can't read the buffer of struct page.
>>
>> Since version 1.5.4 makedumpfile seems to loop in __exclude_unnecessary_pages().
>>
>> We thought about several ways to fix this problem but have not found a
>> good solution up to now.
>>
>> Do you have an idea how we could fix that?
>>
>> Best Regards,
>> Michael
>>
>
>At least on x86, makedumpfile appears to work well for dumps generated by sadump and virsh dump. In particular, virsh
>dump --memory-only generates dump in ELF, whose PT_LOAD entries are generated from RAM list managed by qemu, not managed
>by kernel.
>
>Looking into source code a little, max_mapnr is used only for calculating a size of two bitmaps. I guess there's any
>s390-specific issue.

On second thought, Michael's log looks strange.

>> Excluding unnecessary pages        : [ 21 %] vtop_s390x: Address too big for the number of page table levels.
>> readmem: Can't convert a virtual address(8000180104670) to physical address.
>> readmem: type_addr: 0, addr:8000180104670, size:32768
>> __exclude_unnecessary_pages: Can't read the buffer of struct page.

This message was shown during translating the virtual address of mem_map
to the physical address:

__exclude_unnecessary_pages():

        if (!readmem(VADDR, mem_map,
            page_cache + (index_pg * SIZE(page)),
            SIZE(page) * pfn_mm)) {
                ERRMSG("Can't read the buffer of struct page.\n");
                return FALSE;
        }

However, this should succeed even if mem= was specified because the
corresponding page table must exist in the memory image since it was
used by kernel actually. The address translation logic may have an issue.


Thanks
Atsushi Kumagai

>--
>Thanks.
>HATAYAMA, Daisuke
>
>
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