On 7/7/2025 6:21 AM, Zhuo, Qiuxu wrote:

quoted

From: Sohil Mehta <redacted>
[...]
Vector 2 is reserved for external NMIs corresponding to the Local APIC -
LINT1 pin. Some third-party chipsets may send NMI messages with a fixed
vector value of 2. Using vector 2 for something else would lead to confusion
about the exact source. Do not assign it to any handler.

NMI-source vectors are only assigned for NMI_LOCAL type handlers.
Platform NMI handlers have a single handler registered per type. They don't

From the current NMI code point of view [1] or [2],
a type of platform NMI handler may have multiple handlers registered. 

[1] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/nmi.c#n199
[2] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/nmi.c#n201

We have warnings that should flag any time multiple handlers are
registered for SERR or IO_CHK:

	/*
	 * Indicate if there are multiple registrations on the
	 * internal NMI handler call chains (SERR and IO_CHECK).
	 */
	WARN_ON_ONCE(type == NMI_SERR && !list_empty(&desc->head));
	WARN_ON_ONCE(type == NMI_IO_CHECK && !list_empty(&desc->head));

quoted

need additional source information to differentiate among them.

[...]