linux-kernel - [PATCH V4] Documentation: Improve crash_kexec_post

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Message-ID: <20241027204159.985163-1-gpiccoli@igalia.com>
Date: Sun, 27 Oct 2024 17:36:58 -0300
From: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To: kexec@...ts.infradead.org,
	linux-doc@...r.kernel.org
Cc: bhe@...hat.com,
	vgoyal@...hat.com,
	dyoung@...hat.com,
	corbet@....net,
	linux-kernel@...r.kernel.org,
	linux-debuggers@...r.kernel.org,
	stephen.s.brennan@...cle.com,
	horms@...nel.org,
	kernel@...ccoli.net,
	kernel-dev@...lia.com,
	mhklinux@...look.com,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>
Subject: [PATCH V4] Documentation: Improve crash_kexec_post_notifiers description

The crash_kexec_post_notifiers description could be improved a bit,
by clarifying its upsides (yes, there are some!) and be more descriptive
about the downsides, specially mentioning code that enables the option
unconditionally, like Hyper-V[0], PowerPC (fadump)[1] and more recently,
AMD SEV-SNP[2].

[0] Commit a11589563e96 ("x86/Hyper-V: Report crash register data or kmsg before running crash kernel").
[1] Commit 06e629c25daa ("powerpc/fadump: Fix inaccurate CPU state info in vmcore generated with panic").
[2] Commit 8ef979584ea8 ("crypto: ccp: Add panic notifier for SEV/SNP firmware shutdown on kdump").

Reviewed-by: Stephen Brennan <stephen.s.brennan@...cle.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
---


V4:
* s/AMD SEV/AMD SEV-SNP/ for better clarity, since there are more variants
of AMD SEV - thanks a lot Michael Kelley for the good explanation.

V3 link, including interesting clarifications about AMD SEV variants, by
Michael: https://lore.kernel.org/r/20241025162042.905104-1-gpiccoli@igalia.com/


 Documentation/admin-guide/kernel-parameters.txt | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3978fb704c53..1dbd0b0df6fe 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -918,12 +918,16 @@
 			the parameter has no effect.
 
 	crash_kexec_post_notifiers
-			Run kdump after running panic-notifiers and dumping
-			kmsg. This only for the users who doubt kdump always
-			succeeds in any situation.
-			Note that this also increases risks of kdump failure,
-			because some panic notifiers can make the crashed
-			kernel more unstable.
+			Only jump to kdump kernel after running the panic
+			notifiers and dumping kmsg. This option increases
+			the risks of a kdump failure, since some panic
+			notifiers can make the crashed kernel more unstable.
+			In configurations where kdump may not be reliable,
+			running the panic notifiers could allow collecting
+			more data on dmesg, like stack traces from other CPUS
+			or extra data dumped by panic_print. Note that some
+			configurations enable this option unconditionally,
+			like Hyper-V, PowerPC (fadump) and AMD SEV-SNP.
 
 	crashkernel=size[KMG][@offset[KMG]]
 			[KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
-- 
2.46.2