FAILED: patch "[PATCH] x86/apic: Fix restoring boot IRQ mode in reboot and" failed to apply to 4.16-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.16-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 339b2ae0cd5d4a58f9efe06e4ee36adbeca59228 Mon Sep 17 00:00:00 2001
From: Baoquan He <bhe@redhat.com>
Date: Wed, 14 Feb 2018 13:46:53 +0800
Subject: [PATCH] x86/apic: Fix restoring boot IRQ mode in reboot and
 kexec/kdump

This is a regression fix.

Before, to fix erratum AVR31, the following commit:

  522e66464467 ("x86/apic: Disable I/O APIC before shutdown of the local APIC")

... moved the lapic_shutdown() call to after disable_IO_APIC() in the reboot
and kexec/kdump code paths.

This introduced the following regression: disable_IO_APIC() not only clears
the IO-APIC, but it also restores boot IRQ mode by setting the
LAPIC/APIC/IMCR, calling lapic_shutdown() after disable_IO_APIC() will
disable LAPIC and ruin the possible virtual wire mode setting which
the code has been trying to do all along.

The consequence is that a KVM guest kernel always prints the warning below
during kexec/kdump as the kernel boots up:

  [    0.001000] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/apic/apic.c:1467 setup_local_APIC+0x228/0x330
  [    ........]
  [    0.001000] Call Trace:
  [    0.001000]  apic_bsp_setup+0x56/0x74
  [    0.001000]  x86_late_time_init+0x11/0x16
  [    0.001000]  start_kernel+0x3c9/0x486
  [    0.001000]  secondary_startup_64+0xa5/0xb0
  [    ........]
  [    0.001000] masked ExtINT on CPU#0

To fix this, just call clear_IO_APIC() to stop the IO-APIC where
disable_IO_APIC() was called, and call restore_boot_irq_mode() to
restore boot IRQ mode before a reboot or a kexec/kdump jump.

Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: douly.fnst@cn.fujitsu.com
Cc: joro@8bytes.org
Cc: prarit@redhat.com
Cc: stable@vger.kernel.org
Cc: uobergfe@redhat.com
Fixes: commit 522e66464467 ("x86/apic: Disable I/O APIC before shutdown of the local APIC")
Link: http://lkml.kernel.org/r/20180214054656.3780-4-bhe@redhat.com
[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 10e74d4778a1..1f6680427ff0 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -199,9 +199,10 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 #ifdef CONFIG_X86_IO_APIC
 	/* Prevent crash_kexec() from deadlocking on ioapic_lock. */
 	ioapic_zap_locks();
-	disable_IO_APIC();
+	clear_IO_APIC();
 #endif
 	lapic_shutdown();
+	restore_boot_irq_mode();
 #ifdef CONFIG_HPET_TIMER
 	hpet_disable();
 #endif
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 2126b9d27c34..725624b6c0c0 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -666,7 +666,7 @@ void native_machine_shutdown(void)
 	 * Even without the erratum, it still makes sense to quiet IO APIC
 	 * before disabling Local APIC.
 	 */
-	disable_IO_APIC();
+	clear_IO_APIC();
 #endif
 
 #ifdef CONFIG_SMP
@@ -680,6 +680,7 @@ void native_machine_shutdown(void)
 #endif
 
 	lapic_shutdown();
+	restore_boot_irq_mode();
 
 #ifdef CONFIG_HPET_TIMER
 	hpet_disable();