[PATCH V4] Documentation: Improve crash_kexec_post_notifiers description

[PATCH V4] Documentation: Improve crash_kexec_post_notifiers description

[Guilherme G. Piccoli]

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@oracle.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.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

RE: [PATCH V4] Documentation: Improve crash_kexec_post_notifiers description

[Michael Kelley]

From: Guilherme G. Piccoli <gpiccoli@igalia.com> Sent: Sunday, October 27, 2024 1:37 PM
> 
> 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@oracle.com>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.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/all/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

Reviewed-by: Michael Kelley <mhklinux@outlook.com>

Re: [PATCH V4] Documentation: Improve crash_kexec_post_notifiers description

[Jonathan Corbet]

"Guilherme G. Piccoli" <gpiccoli@igalia.com> writes:

> 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@oracle.com>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
> ---

Applied, thanks.

jon