p2m stuff and crash tool
by Daniel Kiper
Hey Juergen,
As I saw you are strongly playing with p2m stuff, so,
I hope that you can enlighten me a bit in that area.
OVM, Oracle product, uses as dom0 kernel Linux 3.8.13
(yep, I know this is very ancient stuff) with a lot of
backports. Among them there is commit 2c185687ab016954557aac80074f5d7f7f5d275c
(x86/xen: delay construction of mfn_list_list). After
an investigation I discovered that it breaks crash tool.
It fails with following message:
crash: read error: kernel virtual address: ffff88027ce0b700 type: "current_task (per_cpu)"
crash: read error: kernel virtual address: ffff88027ce2b700 type: "current_task (per_cpu)"
crash: read error: kernel virtual address: ffff88027ce4b700 type: "current_task (per_cpu)"
crash: read error: kernel virtual address: ffff88027ce6b700 type: "current_task (per_cpu)"
crash: read error: kernel virtual address: ffff88027ce10c64 type: "tss_struct ist array"
Addresses and symbols depends on a given build.
The problem is that xen_max_p2m_pfn in xen_build_mfn_list_list()
is equal to xen_start_info->nr_pages. This means that memory
which is above due to some remapping/relocation (usually it is
small fraction) is not mapped via p2m_top_mfn and p2m_top_mfn_p.
I should mention here that Xen is started with e.g. dom0_mem=1g,max:1g.
If I remove max argument then crash works because xen_max_p2m_pfn
is greater than xen_start_info->nr_pages. Additionally, the issue
could be fixed by replacing xen_max_p2m_pfn in xen_build_mfn_list_list()
with max_pfn.
After that I decided to take a look at Linux kernel upstream. I saw
that xen_max_p2m_pfn in xen_build_mfn_list_list() is equal to "the
end of last usable machine memory region available for a given
dom0_mem argument + something", e.g.
For dom0_mem=1g,max:1g:
(XEN) Xen-e820 RAM map:
(XEN) 0000000000000000 - 000000000009fc00 (usable)
(XEN) 000000000009fc00 - 00000000000a0000 (reserved)
(XEN) 00000000000f0000 - 0000000000100000 (reserved)
(XEN) 0000000000100000 - 000000007ffdf000 (usable) <--- HERE
(XEN) 000000007ffdf000 - 0000000080000000 (reserved)
(XEN) 00000000b0000000 - 00000000c0000000 (reserved)
(XEN) 00000000feffc000 - 00000000ff000000 (reserved)
(XEN) 00000000fffc0000 - 0000000100000000 (reserved)
(XEN) 0000000100000000 - 0000000180000000 (usable)
Hence xen_max_p2m_pfn == 0x80000
Later I reviewed most of your p2m related commits and I realized
that you played whack-a-mole game with p2m bugs. Sadly, I was not
able to identify exactly one (or more) commit which would fix the
same issue (well, there are some which fixes similar stuff but not
the same one described above). So, if you explain to me why
xen_max_p2m_pfn is set to that value and does not e.g. max_pfn then
it will be much easier for me to write proper fix and maybe fix
the same issue in upstream kernel if it is needed (well, crash
tool does not work with new p2m layout so first of all I must fix it;
I hope that you will help me to that sooner or later).
Additionally, during that work I realized that p2m_top (xen_p2m_addr
in latest Linux kernel) and p2m_top_mfn differs. As I saw p2m_top
represents all stuff (memory, missing, identity, etc.) found in PV
guest address space. However, p2m_top_mfn is just limited to memory
and missing things. Taking into account that p2m_top_mfn is used just
for migration and crash tool it looks that it is sufficient. Am I correct?
Am I not missing any detail?
Daniel
PS I am sending this to wider forum because I think that it
is worth spreading knowledge even if it is not strictly
related to latest Xen or Linux kernel developments.
8 years, 4 months
- 2
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crash-utility for inspecting FreeBSD VM dump
by Miao Jincheng
Hi everyone,
I am curious for inspecting FreeBSD VM dump by crash-utility.
I built crash from source, and changed the configure option of gdb to target FreeBSD.
And used virsh dump --memory-only to generate freebsd.dump.
But I got an obstacle when use this crash utility to load FreeBSD dump:
# ./crash/crash ./kernel.debug ./freebsd.dump
crash 7.1.4
Copyright (C) 2002-2015 Red Hat, Inc.
Copyright (C) 2004, 2005, 2006, 2010 IBM Corporation
Copyright (C) 1999-2006 Hewlett-Packard Co
Copyright (C) 2005, 2006, 2011, 2012 Fujitsu Limited
Copyright (C) 2006, 2007 VA Linux Systems Japan K.K.
Copyright (C) 2005, 2011 NEC Corporation
Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions. Enter "help copying" to see the conditions.
This program has absolutely no warranty. Enter "help warranty" for details.
GNU gdb (GDB) 7.6
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=x86_64-unknown-linux-gnu --target=x86_64-free bsd"...
crash: ./kernel.debug: no debugging data available
But this kernel.debug does have the debug sections:
# readelf --sections ./kernel.debug | grep -i debug
[39] .debug_aranges PROGBITS 0000000000000000 010e500b
[40] .debug_pubnames PROGBITS 0000000000000000 0110d7eb
[41] .debug_info PROGBITS 0000000000000000 012197dd
[42] .debug_abbrev PROGBITS 0000000000000000 034485ff
[43] .debug_line PROGBITS 0000000000000000 03557e9f
[44] .debug_frame PROGBITS 0000000000000000 0387a408
[45] .debug_str PROGBITS 0000000000000000 03985a90
[46] .debug_loc PROGBITS 0000000000000000 03b92d35
[47] .debug_pubtypes PROGBITS 0000000000000000 049b94f1
[48] .debug_ranges PROGBITS 0000000000000000 04da98be
So how is it possible to use crash to load FreeBSD dump?
Thanks in advance.
Jincheng Miao
8 years, 4 months
- 2
- 2