Merge tag 'x86_misc_for_v6.9_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull misc x86 fixes from Borislav Petkov:

 - Fix a wrong check in the function reporting whether a CPU executes
   (or not) a NMI handler

 - Ratelimit unknown NMIs messages in order to not potentially slow down
   the machine

 - Other fixlets

* tag 'x86_misc_for_v6.9_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/nmi: Fix the inverse "in NMI handler" check
  Documentation/maintainer-tip: Add C++ tail comments exception
  Documentation/maintainer-tip: Add Closes tag
  x86/nmi: Rate limit unknown NMI messages
  Documentation/kernel-parameters: Add spec_rstack_overflow to mitigations=off

Documentation/admin-guide/kernel-parameters.txt

@@ -3395,6 +3395,7 @@
 					       nospectre_v1 [X86,PPC]
 					       nospectre_v2 [X86,PPC,S390,ARM64]
 					       retbleed=off [X86]
+					       spec_rstack_overflow=off [X86]
 					       spec_store_bypass_disable=off [X86,PPC]
 					       spectre_v2_user=off [X86]
 					       srbds=off [X86,INTEL]

Documentation/process/maintainer-tip.rst

@@ -304,13 +304,15 @@ following tag ordering scheme:
 
  - Reported-by: ``Reporter <reporter@mail>``
 
+ - Closes: ``URL or Message-ID of the bug report this is fixing``
+
  - Originally-by: ``Original author <original-author@mail>``
 
  - Suggested-by: ``Suggester <suggester@mail>``
 
  - Co-developed-by: ``Co-author <co-author@mail>``
 
-   Signed-off: ``Co-author <co-author@mail>``
+   Signed-off-by: ``Co-author <co-author@mail>``
 
    Note, that Co-developed-by and Signed-off-by of the co-author(s) must
    come in pairs.
@@ -478,7 +480,7 @@ Multi-line comments::
 	 * Larger multi-line comments should be split into paragraphs.
 	 */
 
-No tail comments:
+No tail comments (see below):
 
   Please refrain from using tail comments. Tail comments disturb the
   reading flow in almost all contexts, but especially in code::
@@ -499,6 +501,34 @@ No tail comments:
 	/* This magic initialization needs a comment. Maybe not? */
 	seed = MAGIC_CONSTANT;
 
+  Use C++ style, tail comments when documenting structs in headers to
+  achieve a more compact layout and better readability::
+
+        // eax
+        u32     x2apic_shift    :  5, // Number of bits to shift APIC ID right
+                                      // for the topology ID at the next level
+                                : 27; // Reserved
+        // ebx
+        u32     num_processors  : 16, // Number of processors at current level
+                                : 16; // Reserved
+
+  versus::
+
+	/* eax */
+	        /*
+	         * Number of bits to shift APIC ID right for the topology ID
+	         * at the next level
+	         */
+         u32     x2apic_shift    :  5,
+		 /* Reserved */
+				 : 27;
+
+	/* ebx */
+		/* Number of processors at current level */
+	u32     num_processors  : 16,
+		/* Reserved */
+				: 16;
+
 Comment the important things:
 
   Comments should be added where the operation is not obvious. Documenting

arch/x86/kernel/nmi.c

@@ -304,13 +304,13 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
 
 	__this_cpu_add(nmi_stats.unknown, 1);
 
-	pr_emerg("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",
+	pr_emerg_ratelimited("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",
 			     reason, smp_processor_id());
 
 	if (unknown_nmi_panic || panic_on_unrecovered_nmi)
 		nmi_panic(regs, "NMI: Not continuing");
 
-	pr_emerg("Dazed and confused, but trying to continue\n");
+	pr_emerg_ratelimited("Dazed and confused, but trying to continue\n");
 }
 NOKPROBE_SYMBOL(unknown_nmi_error);
 
@@ -637,7 +637,7 @@ void nmi_backtrace_stall_check(const struct cpumask *btp)
 			msgp = nmi_check_stall_msg[idx];
 			if (nsp->idt_ignored_snap != READ_ONCE(nsp->idt_ignored) && (idx & 0x1))
 				modp = ", but OK because ignore_nmis was set";
-			if (nmi_seq & ~0x1)
+			if (nmi_seq & 0x1)
 				msghp = " (CPU currently in NMI handler function)";
 			else if (nsp->idt_nmi_seq_snap + 1 == nmi_seq)
 				msghp = " (CPU exited one NMI handler function)";