[Patch v2 04/16] x86/apic: Panic if kernel doesn't support x2apic but BIOS has enabled x2apic

[Jiang Liu <jiang.liu@linux.intel.com>]

When kernel doesn't support X2APIC but BIOS has enabled X2APIC, system
may panic or hang without useful messages. On the other hand, it's
hard to dynamically disable X2APIC when CONFIG_X86_X2APIC is disabled.
So panic with a clear message in such a case.

System panics as below when X2APIC is disabled and interrupt remapping
is enabled:
[    0.316118] LAPIC pending interrupts after 512 EOI
[    0.322126] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
[    0.368655] Kernel panic - not syncing: timer doesn't work through Interrupt-remapped IO-APIC
[    0.378300] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.18.0+ #340
[    0.385300] Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS BRIVTIN1.86B.0051.L05.1406240953 06/24/2014
[    0.396997]  ffff88046dc03000 ffff88046c307dd8 ffffffff8179dada 00000000000043f2
[    0.405629]  ffffffff81a92158 ffff88046c307e58 ffffffff8179b757 0000000000000002
[    0.414261]  0000000000000008 ffff88046c307e68 ffff88046c307e08 ffffffff813ad82b
[    0.422890] Call Trace:
[    0.425711]  [<ffffffff8179dada>] dump_stack+0x45/0x57
[    0.431533]  [<ffffffff8179b757>] panic+0xc1/0x1f5
[    0.436978]  [<ffffffff813ad82b>] ? delay_tsc+0x3b/0x70
[    0.442910]  [<ffffffff8166fa2c>] panic_if_irq_remap+0x1c/0x20
[    0.449524]  [<ffffffff81d73645>] setup_IO_APIC+0x405/0x82e
[    0.464979]  [<ffffffff81d6fcc2>] native_smp_prepare_cpus+0x2d9/0x31c
[    0.472274]  [<ffffffff81d5d0ac>] kernel_init_freeable+0xd6/0x223
[    0.479170]  [<ffffffff81792ad0>] ? rest_init+0x80/0x80
[    0.485099]  [<ffffffff81792ade>] kernel_init+0xe/0xf0
[    0.490932]  [<ffffffff817a537c>] ret_from_fork+0x7c/0xb0
[    0.497054]  [<ffffffff81792ad0>] ? rest_init+0x80/0x80
[    0.502983] ---[ end Kernel panic - not syncing: timer doesn't work through Interrupt-remapped IO-APIC

System hangs as below when X2APIC and interrupt remapping are both disabled:
[    1.102782] pci 0000:00:02.0: System wakeup disabled by ACPI
[    1.109351] pci 0000:00:03.0: System wakeup disabled by ACPI
[    1.115915] pci 0000:00:03.2: System wakeup disabled by ACPI
[    1.122479] pci 0000:00:03.3: System wakeup disabled by ACPI
[    1.132274] pci 0000:00:1c.0: Enabling MPC IRBNCE
[    1.137620] pci 0000:00:1c.0: Intel PCH root port ACS workaround enabled
[    1.145239] pci 0000:00:1c.0: System wakeup disabled by ACPI
[    1.151790] pci 0000:00:1c.7: Enabling MPC IRBNCE
[    1.157128] pci 0000:00:1c.7: Intel PCH root port ACS workaround enabled
[    1.164748] pci 0000:00:1c.7: System wakeup disabled by ACPI
[    1.171447] pci 0000:00:1e.0: System wakeup disabled by ACPI
[    1.178612] acpiphp: Slot [8] registered
[    1.183095] pci 0000:00:02.0: PCI bridge to [bus 01]
[    1.188867] acpiphp: Slot [2] registered

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
---
 arch/x86/kernel/apic/apic.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 36249c715da0..8b58e23bc5e8 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1597,6 +1597,14 @@ void __init enable_IR_x2apic(void)
 	int ret, x2apic_enabled = 0;
 	int hardware_init_ret;
 
+	if (!IS_ENABLED(CONFIG_X86_X2APIC)) {
+		u64 msr;
+
+		rdmsrl(MSR_IA32_APICBASE, msr);
+		if (msr & X2APIC_ENABLE)
+			panic("BIOS has enabled x2apic but kernel doesn't support x2apic, please disable x2apic in BIOS.\n");
+	}
+
 	hardware_init_ret = irq_remapping_prepare();
 	if (hardware_init_ret && !x2apic_supported())
 		return;
-- 
1.7.10.4