[PATCH v5 3/5] kdump, documentation: describe craskernel CMA reservation

Jiri Bohac
2025-06-12T10:17:41Z

Describe the new crashkernel ",cma" suffix in Documentation/

Signed-off-by: Jiri Bohac <jbohac@suse.cz>
---
Documentation/admin-guide/kdump/kdump.rst | 21 ++++++++++++++++++
.../admin-guide/kernel-parameters.txt | 22 +++++++++++++++++++
2 files changed, 43 insertions(+)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index 1f7f14c6e184..089665731509 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -311,6 +311,27 @@ crashkernel syntax

crashkernel=0,low

+4) crashkernel=size,cma
+
+ Reserve additional crash kernel memory from CMA. This reservation is
+ usable by the first system's userspace memory and kernel movable
+ allocations (memory balloon, zswap). Pages allocated from this memory
+ range will not be included in the vmcore so this should not be used if
+ dumping of userspace memory is intended and it has to be expected that
+ some movable kernel pages may be missing from the dump.
+
+ A standard crashkernel reservation, as described above, is still needed
+ to hold the crash kernel and initrd.
+
+ This option increases the risk of a kdump failure: DMA transfers
+ configured by the first kernel may end up corrupting the second
+ kernel's memory.
+
+ This reservation method is intended for systems that can't afford to
+ sacrifice enough memory for standard crashkernel reservation and where
+ less reliable and possibly incomplete kdump is preferable to no kdump at
+ all.
+
Boot into System Kernel
-----------------------
1) Update the boot loader (such as grub, yaboot, or lilo) configuration
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ea81784be981..ee6be52dd8a5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -983,6 +983,28 @@
0: to disable low allocation.
It will be ignored when crashkernel=X,high is not used
or memory reserved is below 4G.
+ crashkernel=size[KMG],cma
+ [KNL, X86] Reserve additional crash kernel memory from
+ CMA. This reservation is usable by the first system's
+ userspace memory and kernel movable allocations (memory
+ balloon, zswap). Pages allocated from this memory range
+ will not be included in the vmcore so this should not
+ be used if dumping of userspace memory is intended and
+ it has to be expected that some movable kernel pages
+ may be missing from the dump.
+
+ A standard crashkernel reservation, as described above,
+ is still needed to hold the crash kernel and initrd.
+
+ This option increases the risk of a kdump failure: DMA
+ transfers configured by the first kernel may end up
+ corrupting the second kernel's memory.
+
+ This reservation method is intended for systems that
+ can't afford to sacrifice enough memory for standard
+ crashkernel reservation and where less reliable and
+ possibly incomplete kdump is preferable to no kdump at
+ all.

cryptomgr.notests
[KNL] Disable crypto self-tests

--
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, Prague, Czechia