Re: [PATCH v6 5/9] x86/nmi: Add support to handle NMIs with source information

[Xin Li]

On 5/13/2025 1:37 PM, Sohil Mehta wrote:
> The NMI-source bitmap is delivered as FRED event data to the kernel.
> When available, use NMI-source based filtering to determine the exact
> handlers to run.
>
> Activate NMI-source based filtering only for Local NMIs. While handling
> platform NMI types (such as SERR and IOCHK), do not use the source
> bitmap. They have only one handler registered per type, so there is no
> need to disambiguate between multiple handlers.
>
> Some third-party chipsets may send NMI messages with a hardcoded vector
> of 2, which would result in bit 2 being set in the NMI-source bitmap.
> Skip the local NMI handlers in this situation.
>
> Bit 0 of the source bitmap is set by the hardware whenever a source
> vector was not used while generating an NMI, or the originator could not
> be reliably identified. Poll all the registered handlers in that case.
>
> When multiple handlers need to be executed, adhere to the existing
> priority scheme and execute the handlers registered with NMI_FLAG_FIRST
> before others.
>
> The logic for handling legacy NMIs is unaffected since the source bitmap
> would always have all bits set.
>
> Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>

Reviewed-by: Xin Li (Intel) <xin@xxxxxxxxx>