x86/microcode: Deprecate MICROCODE_OLD_INTERFACE

This is the ancient loading interface which requires special tools to be
used. The bigger problem with it is that it is as inadequate for proper
loading of microcode as the late microcode loading interface is because
it happens just as late.

iucode_tool's manpage already warns people that it is deprecated.

Deprecate it and turn it off by default along with a big fat warning in
the Kconfig help. It will go away sometime in the future.

Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]

arch/x86/Kconfig

@@ -1330,8 +1330,16 @@ config MICROCODE_AMD
 	  processors will be enabled.
 
 config MICROCODE_OLD_INTERFACE
-	def_bool y
+	bool "Ancient loading interface (DEPRECATED)"
+	default n
 	depends on MICROCODE
+	---help---
+	  DO NOT USE THIS! This is the ancient /dev/cpu/microcode interface
+	  which was used by userspace tools like iucode_tool and microcode.ctl.
+	  It is inadequate because it runs too late to be able to properly
+	  load microcode on a machine and it needs special tools. Instead, you
+	  should've switched to the early loading method with the initrd or
+	  builtin microcode by now: Documentation/x86/microcode.txt
 
 config X86_MSR
 	tristate "/dev/cpu/*/msr - Model-specific register support"