x86/microcode/intel: Clear patch pointer before jettisoning the initrd

During early boot, load_ucode_intel_ap() uses __load_ucode_intel()
to obtain a pointer to the relevant microcode patch (embedded in the
initrd), and stores this value in 'intel_ucode_patch' to speed up the
microcode patch application for subsequent CPUs.

On resuming from suspend-to-RAM, however, load_ucode_ap() calls
load_ucode_intel_ap() for each non-boot-CPU. By then the initramfs is
long gone so the pointer stored in 'intel_ucode_patch' no longer points to
a valid microcode patch.

Clear that pointer so that we effectively fall back to the CPU hotplug
notifier callbacks to update the microcode.
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
[ Edit and massage commit message. ]
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org> # 4.10..
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170607095819.9754-1-bp@alien8.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/microcode/intel.c

@@ -619,6 +619,9 @@ int __init save_microcode_in_initrd_intel(void)
 
 	show_saved_mc();
 
+	/* initrd is going away, clear patch ptr. */
+	intel_ucode_patch = NULL;
+
 	return 0;
 }