linux/arch/x86/kernel/reboot.c
Matt Fleming 44be28e9dd x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
It appears that the BayTrail-T class of hardware requires EFI in order
to powerdown and reboot and no other reliable method exists.

This quirk is generally applicable to all hardware that has the ACPI
Hardware Reduced bit set, since usually ACPI would be the preferred
method.

Cc: Len Brown <len.brown@intel.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
2014-07-18 21:23:52 +01:00

786 lines
20 KiB
C

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/reboot.h>
#include <linux/init.h>
#include <linux/pm.h>
#include <linux/efi.h>
#include <linux/dmi.h>
#include <linux/sched.h>
#include <linux/tboot.h>
#include <linux/delay.h>
#include <acpi/reboot.h>
#include <asm/io.h>
#include <asm/apic.h>
#include <asm/desc.h>
#include <asm/hpet.h>
#include <asm/pgtable.h>
#include <asm/proto.h>
#include <asm/reboot_fixups.h>
#include <asm/reboot.h>
#include <asm/pci_x86.h>
#include <asm/virtext.h>
#include <asm/cpu.h>
#include <asm/nmi.h>
#include <asm/smp.h>
#include <linux/ctype.h>
#include <linux/mc146818rtc.h>
#include <asm/realmode.h>
#include <asm/x86_init.h>
#include <asm/efi.h>
/*
* Power off function, if any
*/
void (*pm_power_off)(void);
EXPORT_SYMBOL(pm_power_off);
static const struct desc_ptr no_idt = {};
/*
* This is set if we need to go through the 'emergency' path.
* When machine_emergency_restart() is called, we may be on
* an inconsistent state and won't be able to do a clean cleanup
*/
static int reboot_emergency;
/* This is set by the PCI code if either type 1 or type 2 PCI is detected */
bool port_cf9_safe = false;
/*
* Reboot options and system auto-detection code provided by
* Dell Inc. so their systems "just work". :-)
*/
/*
* Some machines require the "reboot=b" or "reboot=k" commandline options,
* this quirk makes that automatic.
*/
static int __init set_bios_reboot(const struct dmi_system_id *d)
{
if (reboot_type != BOOT_BIOS) {
reboot_type = BOOT_BIOS;
pr_info("%s series board detected. Selecting %s-method for reboots.\n",
d->ident, "BIOS");
}
return 0;
}
void __noreturn machine_real_restart(unsigned int type)
{
local_irq_disable();
/*
* Write zero to CMOS register number 0x0f, which the BIOS POST
* routine will recognize as telling it to do a proper reboot. (Well
* that's what this book in front of me says -- it may only apply to
* the Phoenix BIOS though, it's not clear). At the same time,
* disable NMIs by setting the top bit in the CMOS address register,
* as we're about to do peculiar things to the CPU. I'm not sure if
* `outb_p' is needed instead of just `outb'. Use it to be on the
* safe side. (Yes, CMOS_WRITE does outb_p's. - Paul G.)
*/
spin_lock(&rtc_lock);
CMOS_WRITE(0x00, 0x8f);
spin_unlock(&rtc_lock);
/*
* Switch back to the initial page table.
*/
#ifdef CONFIG_X86_32
load_cr3(initial_page_table);
#else
write_cr3(real_mode_header->trampoline_pgd);
#endif
/* Jump to the identity-mapped low memory code */
#ifdef CONFIG_X86_32
asm volatile("jmpl *%0" : :
"rm" (real_mode_header->machine_real_restart_asm),
"a" (type));
#else
asm volatile("ljmpl *%0" : :
"m" (real_mode_header->machine_real_restart_asm),
"D" (type));
#endif
unreachable();
}
#ifdef CONFIG_APM_MODULE
EXPORT_SYMBOL(machine_real_restart);
#endif
/*
* Some Apple MacBook and MacBookPro's needs reboot=p to be able to reboot
*/
static int __init set_pci_reboot(const struct dmi_system_id *d)
{
if (reboot_type != BOOT_CF9_FORCE) {
reboot_type = BOOT_CF9_FORCE;
pr_info("%s series board detected. Selecting %s-method for reboots.\n",
d->ident, "PCI");
}
return 0;
}
static int __init set_kbd_reboot(const struct dmi_system_id *d)
{
if (reboot_type != BOOT_KBD) {
reboot_type = BOOT_KBD;
pr_info("%s series board detected. Selecting %s-method for reboot.\n",
d->ident, "KBD");
}
return 0;
}
/*
* This is a single dmi_table handling all reboot quirks.
*/
static struct dmi_system_id __initdata reboot_dmi_table[] = {
/* Acer */
{ /* Handle reboot issue on Acer Aspire one */
.callback = set_kbd_reboot,
.ident = "Acer Aspire One A110",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
DMI_MATCH(DMI_PRODUCT_NAME, "AOA110"),
},
},
/* Apple */
{ /* Handle problems with rebooting on Apple MacBook5 */
.callback = set_pci_reboot,
.ident = "Apple MacBook5",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "MacBook5"),
},
},
{ /* Handle problems with rebooting on Apple MacBookPro5 */
.callback = set_pci_reboot,
.ident = "Apple MacBookPro5",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "MacBookPro5"),
},
},
{ /* Handle problems with rebooting on Apple Macmini3,1 */
.callback = set_pci_reboot,
.ident = "Apple Macmini3,1",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Macmini3,1"),
},
},
{ /* Handle problems with rebooting on the iMac9,1. */
.callback = set_pci_reboot,
.ident = "Apple iMac9,1",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "iMac9,1"),
},
},
/* ASUS */
{ /* Handle problems with rebooting on ASUS P4S800 */
.callback = set_bios_reboot,
.ident = "ASUS P4S800",
.matches = {
DMI_MATCH(DMI_BOARD_VENDOR, "ASUSTeK Computer INC."),
DMI_MATCH(DMI_BOARD_NAME, "P4S800"),
},
},
/* Certec */
{ /* Handle problems with rebooting on Certec BPC600 */
.callback = set_pci_reboot,
.ident = "Certec BPC600",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Certec"),
DMI_MATCH(DMI_PRODUCT_NAME, "BPC600"),
},
},
/* Dell */
{ /* Handle problems with rebooting on Dell DXP061 */
.callback = set_bios_reboot,
.ident = "Dell DXP061",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Dell DXP061"),
},
},
{ /* Handle problems with rebooting on Dell E520's */
.callback = set_bios_reboot,
.ident = "Dell E520",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Dell DM061"),
},
},
{ /* Handle problems with rebooting on the Latitude E5410. */
.callback = set_pci_reboot,
.ident = "Dell Latitude E5410",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E5410"),
},
},
{ /* Handle problems with rebooting on the Latitude E5420. */
.callback = set_pci_reboot,
.ident = "Dell Latitude E5420",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E5420"),
},
},
{ /* Handle problems with rebooting on the Latitude E6320. */
.callback = set_pci_reboot,
.ident = "Dell Latitude E6320",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E6320"),
},
},
{ /* Handle problems with rebooting on the Latitude E6420. */
.callback = set_pci_reboot,
.ident = "Dell Latitude E6420",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E6420"),
},
},
{ /* Handle problems with rebooting on Dell Optiplex 330 with 0KP561 */
.callback = set_bios_reboot,
.ident = "Dell OptiPlex 330",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 330"),
DMI_MATCH(DMI_BOARD_NAME, "0KP561"),
},
},
{ /* Handle problems with rebooting on Dell Optiplex 360 with 0T656F */
.callback = set_bios_reboot,
.ident = "Dell OptiPlex 360",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 360"),
DMI_MATCH(DMI_BOARD_NAME, "0T656F"),
},
},
{ /* Handle problems with rebooting on Dell Optiplex 745's SFF */
.callback = set_bios_reboot,
.ident = "Dell OptiPlex 745",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
},
},
{ /* Handle problems with rebooting on Dell Optiplex 745's DFF */
.callback = set_bios_reboot,
.ident = "Dell OptiPlex 745",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
DMI_MATCH(DMI_BOARD_NAME, "0MM599"),
},
},
{ /* Handle problems with rebooting on Dell Optiplex 745 with 0KW626 */
.callback = set_bios_reboot,
.ident = "Dell OptiPlex 745",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
DMI_MATCH(DMI_BOARD_NAME, "0KW626"),
},
},
{ /* Handle problems with rebooting on Dell OptiPlex 760 with 0G919G */
.callback = set_bios_reboot,
.ident = "Dell OptiPlex 760",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 760"),
DMI_MATCH(DMI_BOARD_NAME, "0G919G"),
},
},
{ /* Handle problems with rebooting on the OptiPlex 990. */
.callback = set_pci_reboot,
.ident = "Dell OptiPlex 990",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 990"),
},
},
{ /* Handle problems with rebooting on Dell 300's */
.callback = set_bios_reboot,
.ident = "Dell PowerEdge 300",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 300/"),
},
},
{ /* Handle problems with rebooting on Dell 1300's */
.callback = set_bios_reboot,
.ident = "Dell PowerEdge 1300",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 1300/"),
},
},
{ /* Handle problems with rebooting on Dell 2400's */
.callback = set_bios_reboot,
.ident = "Dell PowerEdge 2400",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 2400"),
},
},
{ /* Handle problems with rebooting on the Dell PowerEdge C6100. */
.callback = set_pci_reboot,
.ident = "Dell PowerEdge C6100",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell"),
DMI_MATCH(DMI_PRODUCT_NAME, "C6100"),
},
},
{ /* Handle problems with rebooting on the Precision M6600. */
.callback = set_pci_reboot,
.ident = "Dell Precision M6600",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Precision M6600"),
},
},
{ /* Handle problems with rebooting on Dell T5400's */
.callback = set_bios_reboot,
.ident = "Dell Precision T5400",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Precision WorkStation T5400"),
},
},
{ /* Handle problems with rebooting on Dell T7400's */
.callback = set_bios_reboot,
.ident = "Dell Precision T7400",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Precision WorkStation T7400"),
},
},
{ /* Handle problems with rebooting on Dell XPS710 */
.callback = set_bios_reboot,
.ident = "Dell XPS710",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
DMI_MATCH(DMI_PRODUCT_NAME, "Dell XPS710"),
},
},
/* Hewlett-Packard */
{ /* Handle problems with rebooting on HP laptops */
.callback = set_bios_reboot,
.ident = "HP Compaq Laptop",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
DMI_MATCH(DMI_PRODUCT_NAME, "HP Compaq"),
},
},
/* Sony */
{ /* Handle problems with rebooting on Sony VGN-Z540N */
.callback = set_bios_reboot,
.ident = "Sony VGN-Z540N",
.matches = {
DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
DMI_MATCH(DMI_PRODUCT_NAME, "VGN-Z540N"),
},
},
{ }
};
static int __init reboot_init(void)
{
int rv;
/*
* Only do the DMI check if reboot_type hasn't been overridden
* on the command line
*/
if (!reboot_default)
return 0;
/*
* The DMI quirks table takes precedence. If no quirks entry
* matches and the ACPI Hardware Reduced bit is set, force EFI
* reboot.
*/
rv = dmi_check_system(reboot_dmi_table);
if (!rv && efi_reboot_required())
reboot_type = BOOT_EFI;
return 0;
}
core_initcall(reboot_init);
static inline void kb_wait(void)
{
int i;
for (i = 0; i < 0x10000; i++) {
if ((inb(0x64) & 0x02) == 0)
break;
udelay(2);
}
}
static void vmxoff_nmi(int cpu, struct pt_regs *regs)
{
cpu_emergency_vmxoff();
}
/* Use NMIs as IPIs to tell all CPUs to disable virtualization */
static void emergency_vmx_disable_all(void)
{
/* Just make sure we won't change CPUs while doing this */
local_irq_disable();
/*
* We need to disable VMX on all CPUs before rebooting, otherwise
* we risk hanging up the machine, because the CPU ignore INIT
* signals when VMX is enabled.
*
* We can't take any locks and we may be on an inconsistent
* state, so we use NMIs as IPIs to tell the other CPUs to disable
* VMX and halt.
*
* For safety, we will avoid running the nmi_shootdown_cpus()
* stuff unnecessarily, but we don't have a way to check
* if other CPUs have VMX enabled. So we will call it only if the
* CPU we are running on has VMX enabled.
*
* We will miss cases where VMX is not enabled on all CPUs. This
* shouldn't do much harm because KVM always enable VMX on all
* CPUs anyway. But we can miss it on the small window where KVM
* is still enabling VMX.
*/
if (cpu_has_vmx() && cpu_vmx_enabled()) {
/* Disable VMX on this CPU. */
cpu_vmxoff();
/* Halt and disable VMX on the other CPUs */
nmi_shootdown_cpus(vmxoff_nmi);
}
}
void __attribute__((weak)) mach_reboot_fixups(void)
{
}
/*
* To the best of our knowledge Windows compatible x86 hardware expects
* the following on reboot:
*
* 1) If the FADT has the ACPI reboot register flag set, try it
* 2) If still alive, write to the keyboard controller
* 3) If still alive, write to the ACPI reboot register again
* 4) If still alive, write to the keyboard controller again
* 5) If still alive, call the EFI runtime service to reboot
* 6) If no EFI runtime service, call the BIOS to do a reboot
*
* We default to following the same pattern. We also have
* two other reboot methods: 'triple fault' and 'PCI', which
* can be triggered via the reboot= kernel boot option or
* via quirks.
*
* This means that this function can never return, it can misbehave
* by not rebooting properly and hanging.
*/
static void native_machine_emergency_restart(void)
{
int i;
int attempt = 0;
int orig_reboot_type = reboot_type;
unsigned short mode;
if (reboot_emergency)
emergency_vmx_disable_all();
tboot_shutdown(TB_SHUTDOWN_REBOOT);
/* Tell the BIOS if we want cold or warm reboot */
mode = reboot_mode == REBOOT_WARM ? 0x1234 : 0;
*((unsigned short *)__va(0x472)) = mode;
for (;;) {
/* Could also try the reset bit in the Hammer NB */
switch (reboot_type) {
case BOOT_ACPI:
acpi_reboot();
reboot_type = BOOT_KBD;
break;
case BOOT_KBD:
mach_reboot_fixups(); /* For board specific fixups */
for (i = 0; i < 10; i++) {
kb_wait();
udelay(50);
outb(0xfe, 0x64); /* Pulse reset low */
udelay(50);
}
if (attempt == 0 && orig_reboot_type == BOOT_ACPI) {
attempt = 1;
reboot_type = BOOT_ACPI;
} else {
reboot_type = BOOT_EFI;
}
break;
case BOOT_EFI:
efi_reboot(reboot_mode, NULL);
reboot_type = BOOT_BIOS;
break;
case BOOT_BIOS:
machine_real_restart(MRR_BIOS);
/* We're probably dead after this, but... */
reboot_type = BOOT_CF9_SAFE;
break;
case BOOT_CF9_FORCE:
port_cf9_safe = true;
/* Fall through */
case BOOT_CF9_SAFE:
if (port_cf9_safe) {
u8 reboot_code = reboot_mode == REBOOT_WARM ? 0x06 : 0x0E;
u8 cf9 = inb(0xcf9) & ~reboot_code;
outb(cf9|2, 0xcf9); /* Request hard reset */
udelay(50);
/* Actually do the reset */
outb(cf9|reboot_code, 0xcf9);
udelay(50);
}
reboot_type = BOOT_TRIPLE;
break;
case BOOT_TRIPLE:
load_idt(&no_idt);
__asm__ __volatile__("int3");
/* We're probably dead after this, but... */
reboot_type = BOOT_KBD;
break;
}
}
}
void native_machine_shutdown(void)
{
/* Stop the cpus and apics */
#ifdef CONFIG_X86_IO_APIC
/*
* Disabling IO APIC before local APIC is a workaround for
* erratum AVR31 in "Intel Atom Processor C2000 Product Family
* Specification Update". In this situation, interrupts that target
* a Logical Processor whose Local APIC is either in the process of
* being hardware disabled or software disabled are neither delivered
* nor discarded. When this erratum occurs, the processor may hang.
*
* Even without the erratum, it still makes sense to quiet IO APIC
* before disabling Local APIC.
*/
disable_IO_APIC();
#endif
#ifdef CONFIG_SMP
/*
* Stop all of the others. Also disable the local irq to
* not receive the per-cpu timer interrupt which may trigger
* scheduler's load balance.
*/
local_irq_disable();
stop_other_cpus();
#endif
lapic_shutdown();
#ifdef CONFIG_HPET_TIMER
hpet_disable();
#endif
#ifdef CONFIG_X86_64
x86_platform.iommu_shutdown();
#endif
}
static void __machine_emergency_restart(int emergency)
{
reboot_emergency = emergency;
machine_ops.emergency_restart();
}
static void native_machine_restart(char *__unused)
{
pr_notice("machine restart\n");
if (!reboot_force)
machine_shutdown();
__machine_emergency_restart(0);
}
static void native_machine_halt(void)
{
/* Stop other cpus and apics */
machine_shutdown();
tboot_shutdown(TB_SHUTDOWN_HALT);
stop_this_cpu(NULL);
}
static void native_machine_power_off(void)
{
if (pm_power_off) {
if (!reboot_force)
machine_shutdown();
pm_power_off();
}
/* A fallback in case there is no PM info available */
tboot_shutdown(TB_SHUTDOWN_HALT);
}
struct machine_ops machine_ops = {
.power_off = native_machine_power_off,
.shutdown = native_machine_shutdown,
.emergency_restart = native_machine_emergency_restart,
.restart = native_machine_restart,
.halt = native_machine_halt,
#ifdef CONFIG_KEXEC
.crash_shutdown = native_machine_crash_shutdown,
#endif
};
void machine_power_off(void)
{
machine_ops.power_off();
}
void machine_shutdown(void)
{
machine_ops.shutdown();
}
void machine_emergency_restart(void)
{
__machine_emergency_restart(1);
}
void machine_restart(char *cmd)
{
machine_ops.restart(cmd);
}
void machine_halt(void)
{
machine_ops.halt();
}
#ifdef CONFIG_KEXEC
void machine_crash_shutdown(struct pt_regs *regs)
{
machine_ops.crash_shutdown(regs);
}
#endif
#if defined(CONFIG_SMP)
/* This keeps a track of which one is crashing cpu. */
static int crashing_cpu;
static nmi_shootdown_cb shootdown_callback;
static atomic_t waiting_for_crash_ipi;
static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
{
int cpu;
cpu = raw_smp_processor_id();
/*
* Don't do anything if this handler is invoked on crashing cpu.
* Otherwise, system will completely hang. Crashing cpu can get
* an NMI if system was initially booted with nmi_watchdog parameter.
*/
if (cpu == crashing_cpu)
return NMI_HANDLED;
local_irq_disable();
shootdown_callback(cpu, regs);
atomic_dec(&waiting_for_crash_ipi);
/* Assume hlt works */
halt();
for (;;)
cpu_relax();
return NMI_HANDLED;
}
static void smp_send_nmi_allbutself(void)
{
apic->send_IPI_allbutself(NMI_VECTOR);
}
/*
* Halt all other CPUs, calling the specified function on each of them
*
* This function can be used to halt all other CPUs on crash
* or emergency reboot time. The function passed as parameter
* will be called inside a NMI handler on all CPUs.
*/
void nmi_shootdown_cpus(nmi_shootdown_cb callback)
{
unsigned long msecs;
local_irq_disable();
/* Make a note of crashing cpu. Will be used in NMI callback. */
crashing_cpu = safe_smp_processor_id();
shootdown_callback = callback;
atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
/* Would it be better to replace the trap vector here? */
if (register_nmi_handler(NMI_LOCAL, crash_nmi_callback,
NMI_FLAG_FIRST, "crash"))
return; /* Return what? */
/*
* Ensure the new callback function is set before sending
* out the NMI
*/
wmb();
smp_send_nmi_allbutself();
msecs = 1000; /* Wait at most a second for the other cpus to stop */
while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
mdelay(1);
msecs--;
}
/* Leave the nmi callback set */
}
#else /* !CONFIG_SMP */
void nmi_shootdown_cpus(nmi_shootdown_cb callback)
{
/* No other CPUs to shoot down */
}
#endif