[PATCH RFC][makedumpfile 00/10] btf/kallsyms based eppic extension for mm page filtering
Tao Liu
ltao at redhat.com
Tue Jun 10 02:57:33 PDT 2025
A) This patchset will introduce the following features to makedumpfile:
1) Enable eppic script for memory pages filtering.
2) Enable btf and kallsyms for symbol type and address resolving.
3) Port maple tree data structures and functions, primarily used for
vma iteration.
B) The purpose of the features are:
1) Currently makedumpfile filters mm pages based on page flags, because flags
can help to determine one page's usage. But this page-flag-checking method
lacks of flexibility in certain cases, e.g. if we want to filter those mm
pages occupied by GPU during vmcore dumping due to:
a) GPU may be taking a large memory and contains sensitive data;
b) GPU mm pages have no relations to kernel crash and useless for vmcore
analysis.
But there is no GPU mm page specific flags, and apparently we don't need
to create one just for kdump use. A programmable filtering tool is more
suitable for such cases. In addition, different GPU vendors may use
different ways for mm pages allocating, programmable filtering is better
than hard coding these GPU specific logics into makedumpfile in this case.
2) Currently makedumpfile already contains a programmable filtering tool, aka
eppic script, which allows user to write customized code for data erasing.
However it has the following drawbacks:
a) cannot do mm page filtering.
b) need to access to debuginfo of both kernel and modules, which is not
applicable in the 2nd kernel.
c) Poor performance, making vmcore dumping time unacceptable (See
the following performance testing).
makedumpfile need to resolve the dwarf data from debuginfo, to get symbols
types and addresses. In recent kernel there are dwarf alternatives such
as btf/kallsyms which can be used for this purpose. And btf/kallsyms info
are already packed within vmcore, so we can use it directly.
3) Maple tree data structures are used in recent kernels, such as vma
iteration. So maple tree poring is needed.
With these, this patchset introduces an upgraded eppic, which is based on
btf/kallsyms symbol resolving, and is programmable for mm page filtering.
The following info shows its usage and performance, please note the tests
are performed in 1st kernel:
$ time ./makedumpfile -d 31 -l /var/crash/127.0.0.1-2025-06-10-18\:03\:12/vmcore
/tmp/dwarf.out -x /lib/debug/lib/modules/6.11.8-300.fc41.x86_64/vmlinux
--eppic eppic_scripts/filter_amdgpu_mm_pages.c
real 14m6.894s
user 4m16.900s
sys 9m44.695s
$ time ./makedumpfile -d 31 -l /var/crash/127.0.0.1-2025-06-10-18\:03\:12/vmcore
/tmp/btf.out --eppic eppic_scripts/filter_amdgpu_mm_pages.c
real 0m10.672s
user 0m9.270s
sys 0m1.130s
-rw------- 1 root root 367475074 Jun 10 18:06 btf.out
-rw------- 1 root root 367475074 Jun 10 21:05 dwarf.out
-rw-rw-rw- 1 root root 387181418 Jun 10 18:03 /var/crash/127.0.0.1-2025-06-10-18:03:12/vmcore
C) Discussion:
1) GPU types: Currently only tested with amdgpu's mm page filtering, others
are not tested.
2) Code structure: There are some similar code shared by makedumpfile and
crash, such as maple tree data structure, also I planed to port the
btf/kallsyms code to crash as well, so there are code duplications for
crash & makedumpfile. Since I havn't working on crash poring, code change
on btf/kallsyms is expected. How can we share the code, creating a common
library or keep the duplication as it is?
3) OS: The code can work on rhel-10+/rhel9.5+ on x86_64/arm64/s390/ppc64.
Others are not tested.
D) Testing:
1) If you don't want to create your vmcore, you can find a vmcore which I
created with amdgpu mm pages unfiltered [1], the amdgpu mm pages are
allocated by program [2]. You can use the vmcore in 1st kernel to filter
the amdgpu mm pages by the previous performance testing cmdline. To
verify the pages are filtered in crash:
Unfiltered:
crash> search -c "!QAZXSW@#EDC"
ffff96b7fa800000: !QAZXSW@#EDCXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
ffff96b87c800000: !QAZXSW@#EDCXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
crash> rd ffff96b7fa800000
ffff96b7fa800000: 405753585a415121 !QAZXSW@
crash> rd ffff96b87c800000
ffff96b87c800000: 405753585a415121 !QAZXSW@
Filtered:
crash> search -c "!QAZXSW@#EDC"
crash> rd ffff96b7fa800000
rd: page excluded: kernel virtual address: ffff96b7fa800000 type: "64-bit KVADDR"
crash> rd ffff96b87c800000
rd: page excluded: kernel virtual address: ffff96b87c800000 type: "64-bit KVADDR"
2) You can use eppic_scripts/print_all_vma.c against an ordinary vmcore to
test only btf/kallsyms functions by output all VMAs if no amdgpu
vmcores/machine avaliable.
[1]: https://people.redhat.com/~ltao/core/
[2]: https://gist.github.com/liutgnu/a8cbce1c666452f1530e1410d1f352df
Tao Liu (10):
dwarf_info: Support kernel address randomization
dwarf_info: Fix a infinite recursion bug for search_domain
Add page filtering function
Add btf/kallsyms support for symbol type/address resolving
Export necessary btf/kallsyms functions to eppic extension
Port the maple tree data structures and functions
Supporting main() as the entry of eppic script
Enable page filtering for dwarf eppic
Enable page filtering for btf/kallsyms eppic
Introducing 2 eppic scripts to test the dwarf/btf eppic extension
Makefile | 6 +-
btf.c | 919 +++++++++++++++++++++++++
btf.h | 176 +++++
dwarf_info.c | 15 +-
eppic_maple.c | 431 ++++++++++++
eppic_maple.h | 8 +
eppic_scripts/filter_amdgpu_mm_pages.c | 36 +
eppic_scripts/print_all_vma.c | 29 +
erase_info.c | 123 +++-
erase_info.h | 22 +
extension_btf.c | 218 ++++++
extension_eppic.c | 41 +-
extension_eppic.h | 6 +-
kallsyms.c | 371 ++++++++++
kallsyms.h | 42 ++
makedumpfile.c | 21 +-
makedumpfile.h | 11 +
17 files changed, 2448 insertions(+), 27 deletions(-)
create mode 100644 btf.c
create mode 100644 btf.h
create mode 100644 eppic_maple.c
create mode 100644 eppic_maple.h
create mode 100644 eppic_scripts/filter_amdgpu_mm_pages.c
create mode 100644 eppic_scripts/print_all_vma.c
create mode 100644 extension_btf.c
create mode 100644 kallsyms.c
create mode 100644 kallsyms.h
--
2.47.0
More information about the kexec
mailing list