[PATCH 11/11] Documentation: admin-guide: kdump: document linux,no-dump DT property

Chen Wandun
2026-04-29T07:00:33Z

Describe the new 'linux,no-dump' reserved-memory device tree property
and the automatic exclusion of /memreserve/ entries from the kdump
vmcore.

The section covers:

- The two mechanisms that exclude reserved memory from the vmcore
(firmware /memreserve/ entries and linux,no-dump child nodes).
- Intended use cases (firmware-owned GPU, DSP and modem carveouts).
- Interaction with the existing 'no-map' and 'reusable' flags, with
the silent-ignore precedence implemented by the kernel.
- Architectures honouring the hint (arm64, riscv, loongarch).
- An illustrative reserved-memory DTS snippet.

The DT binding for the property itself is maintained in dt-schema.

Signed-off-by: Chen Wandun <chenwandun@lixiang.com>
---
Documentation/admin-guide/kdump/kdump.rst | 59 +++++++++++++++++++++++
1 file changed, 59 insertions(+)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index 7587caadbae1..c2246888e84d 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -600,6 +600,65 @@ with /sys/kernel/config/crash_dm_crypt_keys for setup,
3. After the dump-capture kerne get booted, restore the keys to user keyring
echo yes > /sys/kernel/crash_dm_crypt_keys/restore

+Excluding reserved memory regions from the vmcore (device tree)
+===============================================================
+
+On architectures that boot from a device tree and use kexec_file for
+kdump (arm64, riscv, loongarch), specific reserved memory regions can
+be excluded from the ELF PT_LOAD segments of the crash dump.
+
+Two mechanisms contribute to the exclusion:
+
+1) /memreserve/ entries from the FDT header.
+
+ These are firmware-level memory reservations with no associated
+ device tree node and therefore no driver-level description. Their
+ contents are typically firmware scratch areas that carry no value
+ for kernel crash analysis, so they are excluded from the vmcore
+ automatically.
+
+2) Reserved-memory nodes carrying the 'linux,no-dump' property.
+
+ Device tree authors can add this boolean hint to any
+ /reserved-memory child node to request that the kernel skip that
+ region when constructing the elfcorehdr. This is intended for
+ firmware-owned carveouts such as GPU, DSP and modem memory, whose
+ contents tend to significantly inflate the vmcore without aiding
+ kernel crash analysis.
+
+ Example::
+
+ reserved-memory {
+ #address-cells = <2>;
+ #size-cells = <2>;
+ ranges;
+
+ gpu_fw@a0000000 {
+ reg = <0x0 0xa0000000 0x0 0x01000000>;
+ no-map;
+ linux,no-dump;
+ };
+
+ modem_fw@b0000000 {
+ reg = <0x0 0xb0000000 0x0 0x02000000>;
+ linux,no-dump;
+ };
+ };
+
+Interaction with other reserved-memory flags:
+
+- 'no-map': the region is already absent from the kernel linear map,
+ so it does not appear in the vmcore to begin with. Combining
+ 'linux,no-dump' with 'no-map' is harmless but redundant.
+
+- 'reusable': the region is actively used by the kernel for movable
+ page allocations (CMA) and its contents are relevant to crash
+ analysis. 'linux,no-dump' is silently ignored on a reusable region.
+
+The property is an operating-system hint; DTBs that do not set it
+retain the legacy behaviour (all memory is dumped). Architectures
+that do not honour the hint simply ignore it.
+
Contact
=======

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2.43.0