[PATCH v2][makedumpfile 00/14] btf/kallsyms based eppic extension for mm page filtering
Tao Liu
ltao at redhat.com
Sun Nov 23 20:46:37 PST 2025
Kindly ping... Any comments on this?
Thanks,
Tao Liu
On Tue, Oct 21, 2025 at 11:24 AM Tao Liu <ltao at redhat.com> wrote:
>
> 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.
>
> 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.
>
> 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) 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
>
> v2 -> v1:
>
> 1) Moved maple tree related code(for VMA iteration) into eppic script, so we
> don't need to port maple tree code to makedumpfile.
>
> 2) Reorganized the patchset as follows:
>
> --- <common modification> ---
> 1.Add page filtering function
> 2.Supporting main() as the entry of eppic script
>
> --- <dwarf related modification> ---
> 3.dwarf_info: Support kernel address randomization
> 4.dwarf_info: Fix a infinite recursion bug for rust
> 5.eppic dwarf: support anonymous structs member resolving
> 6.Enable page filtering for dwarf eppic
>
> --- <btf & kallsyms related modification> ---
> 7.Implement kernel kallsyms resolving
> 8.Implement kernel btf resolving
> 9.Implement kernel module's kallsyms resolving
> 10.Implement kernel module's btf resolving
> 11.Export necessary btf/kallsyms functions to eppic extension
> 12.Enable page filtering for btf/kallsyms eppic
> 13.Docs: Update eppic related entries
>
> --- <only for test purpose, don't merge> ---
> 14.Introducing 2 eppic scripts to test the dwarf/btf eppic extension
>
> The modification on dwarf is primary for comparision purpose, that
> for the same eppic program, mm page filtering should get exact same
> outputs for dwarf & kallsyms/btf based approaches. If outputs unmatch,
> this indicates bugs. In fact, we will never take dwarf mm pages filtering
> in real use, due to its poor performance as well as inaccessibility
> of debuginfo during kdump in 2nd kernel. So patch 3/4/5 won't affect
> the function of btf/kallsyms eppic mm page filtering, but there are
> functions shared in patch 6, so it is a must-have one. Patch 14 is
> only for test purpose, to demonstrate how to write eppic script for
> mm page filtering, so it isn't a must-have patch.
>
> Please note, in patch 14, I have deliberately converted all array
> operation into pointer operation, e.g. modified "node->slot[i]" into
> "*((unsigned long *)&(node->slot) + i)". This is because there are
> bugs for array operation support in extension_eppic.c. I didn't have
> effort to test and fix them all because as I mentioned previously,
> mm page filtering in dwarf side is only for comparision and will
> never be used in real use. There is no such issue for kallsyms/btf
> eppic side.
>
> 3) Since we ported maple tree code to eppic script, several bugs found
> both for eppic library & eppic btf support. Please use master branch
> of eppic library to co-compile with this patchset.
>
> Tao Liu (14):
> Add page filtering function
> Supporting main() as the entry of eppic script
> dwarf_info: Support kernel address randomization
> dwarf_info: Fix a infinite recursion bug for rust
> eppic dwarf: support anonymous structs member resolving
> Enable page filtering for dwarf eppic
> Implement kernel kallsyms resolving
> Implement kernel btf resolving
> Implement kernel module's kallsyms resolving
> Implement kernel module's btf resolving
> Export necessary btf/kallsyms functions to eppic extension
> Enable page filtering for btf/kallsyms eppic
> Docs: Update eppic related entries
> Introducing 2 eppic scripts to test the dwarf/btf eppic extension
>
> Makefile | 6 +-
> btf.c | 919 +++++++++++++++++++++++++
> btf.h | 177 +++++
> dwarf_info.c | 7 +
> eppic_scripts/filter_amdgpu_mm_pages.c | 255 +++++++
> eppic_scripts/print_all_vma.c | 239 +++++++
> erase_info.c | 120 +++-
> erase_info.h | 19 +
> extension_btf.c | 258 +++++++
> extension_eppic.c | 106 ++-
> extension_eppic.h | 6 +-
> kallsyms.c | 392 +++++++++++
> kallsyms.h | 41 ++
> makedumpfile.8.in | 24 +-
> makedumpfile.c | 21 +-
> makedumpfile.h | 11 +
> print_info.c | 11 +-
> 17 files changed, 2550 insertions(+), 62 deletions(-)
> create mode 100644 btf.c
> create mode 100644 btf.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
>
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