linux-kernel - arm64: pseudo NMI bootconfig question

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Message-ID: <rs4igmsjrm6r2aio4nbe5jos3vcqk2u4bjhltjwtj2pn3cquip@kv3grgec7qrb>
Date: Wed, 12 Nov 2025 06:05:43 -0800
From: Breno Leitao <leitao@...ian.org>
To: catalin.marinas@....com, will@...nel.org, mark.rutland@....com
Cc: paulmck@...nel.org, mhiramat@...nel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: arm64: pseudo NMI bootconfig question

Hello,

In most major Linux distributions, it’s common to have a separate debug kernel
build. This variant is compiled with additional debug configuration options to
provide deeper observability and easier debugging, typically at the expense of
some performance.

This approach is also used in several companies, including mine. The debug
flavor is usually a drop-in replacement deployed when investigating
issues, allowing quicker identification before more detailed manual
debugging.

I’m currently debugging some hung tasks using the debug kernel flavor and
noticed that backtraces weren’t printed correctly because PSEUDO NMI isn’t
enabled.

AFAIK, to enable PSEUDO NMI on ARM, the following are required:

 cmdline: irqchip.gicv3_pseudo_nmi=1
 config: CONFIG_ARM64_PSEUDO_NMI=y

I wanted to have pseudo NMI enabled by default in the debug kernel
(without relying on kernel command-line parameters), but this isn’t
possible today. The reason is that `irqchip.gicv3_pseudo_nmi` is an early
parameter, which can’t be set through bootconfig, so, independent of my
.config, I need to hack cmdline arguments to have the debuggability
I need.

Question:

Would it make sense to provide an option to enable pseudo NMI in certain
kernel configuration without requiring an extra command-line parameter?