x86/nmi: Improve <asm/nmi.h> documentation

NMI handlers can be registered by various subsystems, including drivers.

However, the interface for registering and unregistering such handlers
is not clearly documented. In the future, the interface may need to be
extended to identify the source of the NMI.

Add documentation to make the current API more understandable and easier
to use.

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Link: https://lore.kernel.org/r/20250327234629.3953536-8-sohil.mehta@intel.com

diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index f85aea7bf7f196c07ccfaa324148d41f72b69283..79d88d12c8fbf1c718272aca53eba57515338515 100644 (file)
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -20,8 +20,20 @@ extern int unknown_nmi_panic;
 extern int panic_on_unrecovered_nmi;
 extern int panic_on_io_nmi;
 
+/* NMI handler flags */
 #define NMI_FLAG_FIRST 1
 
+/**
+ * enum - NMI types.
+ * @NMI_LOCAL:    Local NMI, CPU-specific NMI generated by the Local APIC.
+ * @NMI_UNKNOWN:  Unknown NMI, the source of the NMI may not be identified.
+ * @NMI_SERR:     System Error NMI, typically triggered by PCI errors.
+ * @NMI_IO_CHECK: I/O Check NMI, related to I/O errors.
+ * @NMI_MAX:      Maximum value for NMI types.
+ *
+ * NMI types are used to categorize NMIs and to dispatch them to the
+ * appropriate handler.
+ */
 enum {
        NMI_LOCAL=0,
        NMI_UNKNOWN,
@@ -30,6 +42,7 @@ enum {
        NMI_MAX
 };
 
+/* NMI handler return values */
 #define NMI_DONE       0
 #define NMI_HANDLED    1
 
@@ -43,6 +56,25 @@ struct nmiaction {
        const char              *name;
 };
 
+/**
+ * register_nmi_handler - Register a handler for a specific NMI type
+ * @t:    NMI type (e.g. NMI_LOCAL)
+ * @fn:   The NMI handler
+ * @fg:   Flags associated with the NMI handler
+ * @n:    Name of the NMI handler
+ * @init: Optional __init* attributes for struct nmiaction
+ *
+ * Adds the provided handler to the list of handlers for the specified
+ * NMI type. Handlers flagged with NMI_FLAG_FIRST would be executed first.
+ *
+ * Sometimes the source of an NMI can't be reliably determined which
+ * results in an NMI being tagged as "unknown". Register an additional
+ * handler using the NMI type - NMI_UNKNOWN to handle such cases. The
+ * caller would get one last chance to assume responsibility for the
+ * NMI.
+ *
+ * Return: 0 on success, or an error code on failure.
+ */
 #define register_nmi_handler(t, fn, fg, n, init...)    \
 ({                                                     \
        static struct nmiaction init fn##_na = {        \
@@ -56,7 +88,16 @@ struct nmiaction {
 
 int __register_nmi_handler(unsigned int, struct nmiaction *);
 
-void unregister_nmi_handler(unsigned int, const char *);
+/**
+ * unregister_nmi_handler - Unregister a handler for a specific NMI type
+ * @type: NMI type (e.g. NMI_LOCAL)
+ * @name: Name of the NMI handler used during registration
+ *
+ * Removes the handler associated with the specified NMI type from the
+ * NMI handler list. The "name" is used as a lookup key to identify the
+ * handler.
+ */
+void unregister_nmi_handler(unsigned int type, const char *name);
 
 void set_emergency_nmi_handler(unsigned int type, nmi_handler_t handler);