Patch "x86/smpboot: Init apic mapping before usage" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

x86/smpboot: Init apic mapping before usage

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-smpboot-init-apic-mapping-before-usage.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Gleixner <[email protected]>
Date: Sat, 29 Oct 2016 13:42:42 +0200
Subject: x86/smpboot: Init apic mapping before usage

From: Thomas Gleixner <[email protected]>

commit 1e90a13d0c3dc94512af1ccb2b6563e8297838fa upstream.

The recent changes, which forced the registration of the boot cpu on UP systems, which do not have ACPI tables, have been fixed for systems w/o local APIC, but left a wreckage for systems which have neither ACPI nor mptables, but the CPU has an APIC, e.g. virtualbox.

The boot process crashes in prefill_possible_map() as it wants to register the boot cpu, which needs to access the local apic, but the local APIC is not yet mapped.

There is no reason why init_apic_mapping() can't be invoked before prefill_possible_map(). So instead of playing another silly early mapping game, as the ACPI/mptables code does, we just move init_apic_mapping() before the call to prefill_possible_map().

In hindsight, I should have noticed that combination earlier.

Sorry for the churn (also in stable)!

---
 arch/x86/kernel/setup.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

@@ -1222,11 +1222,16 @@ void __init setup_arch(char **cmdline_p)
 	if (smp_found_config)
 		get_smp_config();
 
+	/*
+	 * Systems w/o ACPI and mptables might not have it mapped the local
+	 * APIC yet, but prefill_possible_map() might need to access it.
+	 */
+	init_apic_mappings();
+
 	prefill_possible_map();
 
 	init_cpu_to_node();
 
-	init_apic_mappings();
 	io_apic_init_mappings();
 
 	kvm_guest_init();

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/x86-smpboot-init-apic-mapping-before-usage.patch queue-4.8/x86-microcode-amd-fix-more-fallout-from-config_randomize_memory-y.patch queue-4.8/timers-lock-base-for-same-bucket-optimization.patch queue-4.8/timers-plug-locking-race-vs.-timer-migration.patch queue-4.8/timers-prevent-base-clock-corruption-when-forwarding.patch queue-4.8/timers-prevent-base-clock-rewind-when-forwarding-clock.patch