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

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Message-ID:
 <SN6PR02MB415728E95FEBF7CC79D45B97D4492@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Sun, 27 Oct 2024 22:35:28 +0000
From: Michael Kelley <mhklinux@...look.com>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>, "kexec@...ts.infradead.org"
	<kexec@...ts.infradead.org>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>
CC: "bhe@...hat.com" <bhe@...hat.com>, "vgoyal@...hat.com"
	<vgoyal@...hat.com>, "dyoung@...hat.com" <dyoung@...hat.com>,
	"corbet@....net" <corbet@....net>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-debuggers@...r.kernel.org"
	<linux-debuggers@...r.kernel.org>, "stephen.s.brennan@...cle.com"
	<stephen.s.brennan@...cle.com>, "horms@...nel.org" <horms@...nel.org>,
	"kernel@...ccoli.net" <kernel@...ccoli.net>, "kernel-dev@...lia.com"
	<kernel-dev@...lia.com>
Subject: RE: [PATCH V4] Documentation: Improve crash_kexec_post_notifiers
 description

From: Guilherme G. Piccoli <gpiccoli@...lia.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@...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/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@...look.com>