[GIT PULL] x86 generic hotplug changes for v3.8

From: Ingo Molnar
Date: Tue Dec 11 2012 - 05:38:19 EST

Linus,

Please pull the latest x86-bsp-hotplug-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-bsp-hotplug-for-linus

HEAD: a71c8bc5dfefbbf80ef90739791554ef7ea4401b x86, topology: Debug CPU0 hotplug

This tree enables CPU#0 (the boot processor) to be
onlined/offlined on x86, just like any other CPU. Enabled on
Intel CPUs for now.

Allowing this required the identification and fixing of latent
CPU#0 assumptions (such as CPU#0 initializations, etc.) in the
x86 architecture code, plus the identification of barriers to
BSP-offlining, such as active PIC interrupts which can only be
serviced on the BSP.

It's behind a default-off option, and there's a debug option
that allows the automatic testing of this feature.

The motivation of this feature is to allow and prepare for true
CPU-hotplug hardware support: recent changes to MCE support
enable us to detect a deteriorating but not yet hard-failing
L1/L2 cache on a CPU that could be soft-unplugged - or a failing
L3 cache on a multi-socket system.

Note that true hardware hot-plug is not yet fully enabled by
this, because that requires a special platform wakeup sequence
to be sent to the freshly powered up CPU#0. Future patches for
this are planned, once such a platform exists. Chicken and egg
...

out-of-topic modifications in x86-bsp-hotplug-for-linus:
--------------------------------------------------------
kernel/cpu.c # 6e32d47: kernel/cpu.c: Add comment for pri

Thanks,

Ingo

------------------>
Fenghua Yu (14):
doc: Add x86 CPU0 online/offline feature
x86, Kconfig: Add config switch for CPU0 hotplug
x86, topology: Don't offline CPU0 if any PIC irq can not be migrated out of it
x86, hotplug: Support functions for CPU0 online/offline
x86, hotplug, suspend: Online CPU0 for suspend or hibernate
kernel/cpu.c: Add comment for priority in cpu_hotplug_pm_callback
x86-64, hotplug: Add start_cpu0() entry point to head_64.S
x86-32, hotplug: Add start_cpu0() entry point to head_32.S
x86, hotplug: Wake up CPU0 via NMI instead of INIT, SIPI, SIPI
x86, hotplug: During CPU0 online, enable x2apic, set_numa_node.
x86, hotplug: The first online processor saves the MTRR state
x86, hotplug: Handle retrigger irq by the first available CPU
x86/i387.c: Initialize thread xstate only on CPU0 only once
x86, topology: Debug CPU0 hotplug


Documentation/cpu-hotplug.txt | 24 ++++++
Documentation/kernel-parameters.txt | 14 ++++
arch/x86/Kconfig | 44 +++++++++++
arch/x86/include/asm/cpu.h | 4 +
arch/x86/include/asm/smp.h | 1 +
arch/x86/kernel/apic/io_apic.c | 4 +-
arch/x86/kernel/cpu/common.c | 5 +-
arch/x86/kernel/cpu/mtrr/main.c | 9 ++-
arch/x86/kernel/head_32.S | 13 ++++
arch/x86/kernel/head_64.S | 16 ++++
arch/x86/kernel/i387.c | 6 +-
arch/x86/kernel/smpboot.c | 149 +++++++++++++++++++++++++++++-------
arch/x86/kernel/topology.c | 101 ++++++++++++++++++++++--
arch/x86/power/cpu.c | 82 ++++++++++++++++++++
kernel/cpu.c | 5 ++
15 files changed, 436 insertions(+), 41 deletions(-)

diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index 66ef8f3..9f40135 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -207,6 +207,30 @@ by making it not-removable.

In such cases you will also notice that the online file is missing under cpu0.

+Q: Is CPU0 removable on X86?
+A: Yes. If kernel is compiled with CONFIG_BOOTPARAM_HOTPLUG_CPU0=y, CPU0 is
+removable by default. Otherwise, CPU0 is also removable by kernel option
+cpu0_hotplug.
+
+But some features depend on CPU0. Two known dependencies are:
+
+1. Resume from hibernate/suspend depends on CPU0. Hibernate/suspend will fail if
+CPU0 is offline and you need to online CPU0 before hibernate/suspend can
+continue.
+2. PIC interrupts also depend on CPU0. CPU0 can't be removed if a PIC interrupt
+is detected.
+
+It's said poweroff/reboot may depend on CPU0 on some machines although I haven't
+seen any poweroff/reboot failure so far after CPU0 is offline on a few tested
+machines.
+
+Please let me know if you know or see any other dependencies of CPU0.
+
+If the dependencies are under your control, you can turn on CPU0 hotplug feature
+either by CONFIG_BOOTPARAM_HOTPLUG_CPU0 or by kernel parameter cpu0_hotplug.
+
+--Fenghua Yu <fenghua.yu@xxxxxxxxx>
+
Q: How do i find out if a particular CPU is not removable?
A: Depending on the implementation, some architectures may show this by the
absence of the "online" file. This is done if it can be determined ahead of
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9776f06..f7cbe1d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1984,6 +1984,20 @@ bytes respectively. Such letter suffixes can also be entirely omitted.

nox2apic [X86-64,APIC] Do not enable x2APIC mode.

+ cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
+ CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
+ Some features depend on CPU0. Known dependencies are:
+ 1. Resume from suspend/hibernate depends on CPU0.
+ Suspend/hibernate will fail if CPU0 is offline and you
+ need to online CPU0 before suspend/hibernate.
+ 2. PIC interrupts also depend on CPU0. CPU0 can't be
+ removed if a PIC interrupt is detected.
+ It's said poweroff/reboot may depend on CPU0 on some
+ machines although I haven't seen such issues so far
+ after CPU0 is offline on a few tested machines.
+ If the dependencies are under your control, you can
+ turn on cpu0_hotplug.
+
nptcg= [IA-64] Override max number of concurrent global TLB
purges which is reported from either PAL_VM_SUMMARY or
SAL PALO.
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 46c3bff..b6cfa5f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1698,6 +1698,50 @@ config HOTPLUG_CPU
automatically on SMP systems. )
Say N if you want to disable CPU hotplug.

+config BOOTPARAM_HOTPLUG_CPU0
+ bool "Set default setting of cpu0_hotpluggable"
+ default n
+ depends on HOTPLUG_CPU && EXPERIMENTAL
+ ---help---
+ Set whether default state of cpu0_hotpluggable is on or off.
+
+ Say Y here to enable CPU0 hotplug by default. If this switch
+ is turned on, there is no need to give cpu0_hotplug kernel
+ parameter and the CPU0 hotplug feature is enabled by default.
+
+ Please note: there are two known CPU0 dependencies if you want
+ to enable the CPU0 hotplug feature either by this switch or by
+ cpu0_hotplug kernel parameter.
+
+ First, resume from hibernate or suspend always starts from CPU0.
+ So hibernate and suspend are prevented if CPU0 is offline.
+
+ Second dependency is PIC interrupts always go to CPU0. CPU0 can not
+ offline if any interrupt can not migrate out of CPU0. There may
+ be other CPU0 dependencies.
+
+ Please make sure the dependencies are under your control before
+ you enable this feature.
+
+ Say N if you don't want to enable CPU0 hotplug feature by default.
+ You still can enable the CPU0 hotplug feature at boot by kernel
+ parameter cpu0_hotplug.
+
+config DEBUG_HOTPLUG_CPU0
+ def_bool n
+ prompt "Debug CPU0 hotplug"
+ depends on HOTPLUG_CPU && EXPERIMENTAL
+ ---help---
+ Enabling this option offlines CPU0 (if CPU0 can be offlined) as
+ soon as possible and boots up userspace with CPU0 offlined. User
+ can online CPU0 back after boot time.
+
+ To debug CPU0 hotplug, you need to enable CPU0 offline/online
+ feature by either turning on CONFIG_BOOTPARAM_HOTPLUG_CPU0 during
+ compilation or giving cpu0_hotplug kernel parameter at boot.
+
+ If unsure, say N.
+
config COMPAT_VDSO
def_bool y
prompt "Compat VDSO support"
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 4564c8e..5f9a124 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -28,6 +28,10 @@ struct x86_cpu {
#ifdef CONFIG_HOTPLUG_CPU
extern int arch_register_cpu(int num);
extern void arch_unregister_cpu(int);
+extern void __cpuinit start_cpu0(void);
+#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
+extern int _debug_hotplug_cpu(int cpu, int action);
+#endif
#endif

DECLARE_PER_CPU(int, cpu_state);
diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 4f19a15..b073aae 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -166,6 +166,7 @@ void native_send_call_func_ipi(const struct cpumask *mask);
void native_send_call_func_single_ipi(int cpu);
void x86_idle_thread_init(unsigned int cpu, struct task_struct *idle);

+void smp_store_boot_cpu_info(void);
void smp_store_cpu_info(int id);
#define cpu_physical_id(cpu) per_cpu(x86_cpu_to_apicid, cpu)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 1817fa9..f78fc2b 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2199,9 +2199,11 @@ static int ioapic_retrigger_irq(struct irq_data *data)
{
struct irq_cfg *cfg = data->chip_data;
unsigned long flags;
+ int cpu;

raw_spin_lock_irqsave(&vector_lock, flags);
- apic->send_IPI_mask(cpumask_of(cpumask_first(cfg->domain)), cfg->vector);
+ cpu = cpumask_first_and(cfg->domain, cpu_online_mask);
+ apic->send_IPI_mask(cpumask_of(cpu), cfg->vector);
raw_spin_unlock_irqrestore(&vector_lock, flags);

return 1;
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 7505f7b..ca165ac 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1237,7 +1237,7 @@ void __cpuinit cpu_init(void)
oist = &per_cpu(orig_ist, cpu);

#ifdef CONFIG_NUMA
- if (cpu != 0 && this_cpu_read(numa_node) == 0 &&
+ if (this_cpu_read(numa_node) == 0 &&
early_cpu_to_node(cpu) != NUMA_NO_NODE)
set_numa_node(early_cpu_to_node(cpu));
#endif
@@ -1269,8 +1269,7 @@ void __cpuinit cpu_init(void)
barrier();

x86_configure_nx();
- if (cpu != 0)
- enable_x2apic();
+ enable_x2apic();

/*
* set up and load the per-CPU TSS
diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 6b96110..e4c1a41 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -695,11 +695,16 @@ void mtrr_ap_init(void)
}

/**
- * Save current fixed-range MTRR state of the BSP
+ * Save current fixed-range MTRR state of the first cpu in cpu_online_mask.
*/
void mtrr_save_state(void)
{
- smp_call_function_single(0, mtrr_save_fixed_ranges, NULL, 1);
+ int first_cpu;
+
+ get_online_cpus();
+ first_cpu = cpumask_first(cpu_online_mask);
+ smp_call_function_single(first_cpu, mtrr_save_fixed_ranges, NULL, 1);
+ put_online_cpus();
}

void set_mtrr_aps_delayed_init(void)
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 957a47a..a013e73 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -266,6 +266,19 @@ num_subarch_entries = (. - subarch_entries) / 4
jmp default_entry
#endif /* CONFIG_PARAVIRT */

+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * Boot CPU0 entry point. It's called from play_dead(). Everything has been set
+ * up already except stack. We just set up stack here. Then call
+ * start_secondary().
+ */
+ENTRY(start_cpu0)
+ movl stack_start, %ecx
+ movl %ecx, %esp
+ jmp *(initial_code)
+ENDPROC(start_cpu0)
+#endif
+
/*
* Non-boot CPU entry point; entered from trampoline.S
* We can't lgdt here, because lgdt itself uses a data segment, but
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 94bf9cc..980053c 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -252,6 +252,22 @@ ENTRY(secondary_startup_64)
pushq %rax # target address in negative space
lretq

+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * Boot CPU0 entry point. It's called from play_dead(). Everything has been set
+ * up already except stack. We just set up stack here. Then call
+ * start_secondary().
+ */
+ENTRY(start_cpu0)
+ movq stack_start(%rip),%rsp
+ movq initial_code(%rip),%rax
+ pushq $0 # fake return address to stop unwinder
+ pushq $__KERNEL_CS # set correct cs
+ pushq %rax # target address in negative space
+ lretq
+ENDPROC(start_cpu0)
+#endif
+
/* SMP bootup changes these two */
__REFDATA
.align 8
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 675a050..245a71d 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -175,7 +175,11 @@ void __cpuinit fpu_init(void)
cr0 |= X86_CR0_EM;
write_cr0(cr0);

- if (!smp_processor_id())
+ /*
+ * init_thread_xstate is only called once to avoid overriding
+ * xstate_size during boot time or during CPU hotplug.
+ */
+ if (xstate_size == 0)
init_thread_xstate();

mxcsr_feature_mask_init();
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index c80a33b..ef53e66 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -125,8 +125,8 @@ EXPORT_PER_CPU_SYMBOL(cpu_info);
atomic_t init_deasserted;

/*
- * Report back to the Boot Processor.
- * Running on AP.
+ * Report back to the Boot Processor during boot time or to the caller processor
+ * during CPU online.
*/
static void __cpuinit smp_callin(void)
{
@@ -138,15 +138,17 @@ static void __cpuinit smp_callin(void)
* we may get here before an INIT-deassert IPI reaches
* our local APIC. We have to wait for the IPI or we'll
* lock up on an APIC access.
+ *
+ * Since CPU0 is not wakened up by INIT, it doesn't wait for the IPI.
*/
- if (apic->wait_for_init_deassert)
+ cpuid = smp_processor_id();
+ if (apic->wait_for_init_deassert && cpuid != 0)
apic->wait_for_init_deassert(&init_deasserted);

/*
* (This works even if the APIC is not enabled.)
*/
phys_id = read_apic_id();
- cpuid = smp_processor_id();
if (cpumask_test_cpu(cpuid, cpu_callin_mask)) {
panic("%s: phys CPU#%d, CPU#%d already present??\n", __func__,
phys_id, cpuid);
@@ -228,6 +230,8 @@ static void __cpuinit smp_callin(void)
cpumask_set_cpu(cpuid, cpu_callin_mask);
}

+static int cpu0_logical_apicid;
+static int enable_start_cpu0;
/*
* Activate a secondary processor.
*/
@@ -243,6 +247,8 @@ notrace static void __cpuinit start_secondary(void *unused)
preempt_disable();
smp_callin();

+ enable_start_cpu0 = 0;
+
#ifdef CONFIG_X86_32
/* switch away from the initial page table */
load_cr3(swapper_pg_dir);
@@ -279,19 +285,30 @@ notrace static void __cpuinit start_secondary(void *unused)
cpu_idle();
}

+void __init smp_store_boot_cpu_info(void)
+{
+ int id = 0; /* CPU 0 */
+ struct cpuinfo_x86 *c = &cpu_data(id);
+
+ *c = boot_cpu_data;
+ c->cpu_index = id;
+}
+
/*
* The bootstrap kernel entry code has set these up. Save them for
* a given CPU
*/
-
void __cpuinit smp_store_cpu_info(int id)
{
struct cpuinfo_x86 *c = &cpu_data(id);

*c = boot_cpu_data;
c->cpu_index = id;
- if (id != 0)
- identify_secondary_cpu(c);
+ /*
+ * During boot time, CPU0 has this setup already. Save the info when
+ * bringing up AP or offlined CPU0.
+ */
+ identify_secondary_cpu(c);
}

static bool __cpuinit
@@ -481,7 +498,7 @@ void __inquire_remote_apic(int apicid)
* won't ... remember to clear down the APIC, etc later.
*/
int __cpuinit
-wakeup_secondary_cpu_via_nmi(int logical_apicid, unsigned long start_eip)
+wakeup_secondary_cpu_via_nmi(int apicid, unsigned long start_eip)
{
unsigned long send_status, accept_status = 0;
int maxlvt;
@@ -489,7 +506,7 @@ wakeup_secondary_cpu_via_nmi(int logical_apicid, unsigned long start_eip)
/* Target chip */
/* Boot on the stack */
/* Kick the second */
- apic_icr_write(APIC_DM_NMI | apic->dest_logical, logical_apicid);
+ apic_icr_write(APIC_DM_NMI | apic->dest_logical, apicid);

pr_debug("Waiting for send to finish...\n");
send_status = safe_apic_wait_icr_idle();
@@ -649,6 +666,63 @@ static void __cpuinit announce_cpu(int cpu, int apicid)
node, cpu, apicid);
}

+static int wakeup_cpu0_nmi(unsigned int cmd, struct pt_regs *regs)
+{
+ int cpu;
+
+ cpu = smp_processor_id();
+ if (cpu == 0 && !cpu_online(cpu) && enable_start_cpu0)
+ return NMI_HANDLED;
+
+ return NMI_DONE;
+}
+
+/*
+ * Wake up AP by INIT, INIT, STARTUP sequence.
+ *
+ * Instead of waiting for STARTUP after INITs, BSP will execute the BIOS
+ * boot-strap code which is not a desired behavior for waking up BSP. To
+ * void the boot-strap code, wake up CPU0 by NMI instead.
+ *
+ * This works to wake up soft offlined CPU0 only. If CPU0 is hard offlined
+ * (i.e. physically hot removed and then hot added), NMI won't wake it up.
+ * We'll change this code in the future to wake up hard offlined CPU0 if
+ * real platform and request are available.
+ */
+static int __cpuinit
+wakeup_cpu_via_init_nmi(int cpu, unsigned long start_ip, int apicid,
+ int *cpu0_nmi_registered)
+{
+ int id;
+ int boot_error;
+
+ /*
+ * Wake up AP by INIT, INIT, STARTUP sequence.
+ */
+ if (cpu)
+ return wakeup_secondary_cpu_via_init(apicid, start_ip);
+
+ /*
+ * Wake up BSP by nmi.
+ *
+ * Register a NMI handler to help wake up CPU0.
+ */
+ boot_error = register_nmi_handler(NMI_LOCAL,
+ wakeup_cpu0_nmi, 0, "wake_cpu0");
+
+ if (!boot_error) {
+ enable_start_cpu0 = 1;
+ *cpu0_nmi_registered = 1;
+ if (apic->dest_logical == APIC_DEST_LOGICAL)
+ id = cpu0_logical_apicid;
+ else
+ id = apicid;
+ boot_error = wakeup_secondary_cpu_via_nmi(id, start_ip);
+ }
+
+ return boot_error;
+}
+
/*
* NOTE - on most systems this is a PHYSICAL apic ID, but on multiquad
* (ie clustered apic addressing mode), this is a LOGICAL apic ID.
@@ -664,6 +738,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu, struct task_struct *idle)

unsigned long boot_error = 0;
int timeout;
+ int cpu0_nmi_registered = 0;

/* Just in case we booted with a single CPU. */
alternatives_enable_smp();
@@ -711,13 +786,16 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
}

/*
- * Kick the secondary CPU. Use the method in the APIC driver
- * if it's defined - or use an INIT boot APIC message otherwise:
+ * Wake up a CPU in difference cases:
+ * - Use the method in the APIC driver if it's defined
+ * Otherwise,
+ * - Use an INIT boot APIC message for APs or NMI for BSP.
*/
if (apic->wakeup_secondary_cpu)
boot_error = apic->wakeup_secondary_cpu(apicid, start_ip);
else
- boot_error = wakeup_secondary_cpu_via_init(apicid, start_ip);
+ boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
+ &cpu0_nmi_registered);

if (!boot_error) {
/*
@@ -782,6 +860,13 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
*/
smpboot_restore_warm_reset_vector();
}
+ /*
+ * Clean up the nmi handler. Do this after the callin and callout sync
+ * to avoid impact of possible long unregister time.
+ */
+ if (cpu0_nmi_registered)
+ unregister_nmi_handler(NMI_LOCAL, "wake_cpu0");
+
return boot_error;
}

@@ -795,7 +880,7 @@ int __cpuinit native_cpu_up(unsigned int cpu, struct task_struct *tidle)

pr_debug("++++++++++++++++++++=_---CPU UP %u\n", cpu);

- if (apicid == BAD_APICID || apicid == boot_cpu_physical_apicid ||
+ if (apicid == BAD_APICID ||
!physid_isset(apicid, phys_cpu_present_map) ||
!apic->apic_id_valid(apicid)) {
pr_err("%s: bad cpu %d\n", __func__, cpu);
@@ -990,7 +1075,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
/*
* Setup boot CPU information
*/
- smp_store_cpu_info(0); /* Final full version of the data */
+ smp_store_boot_cpu_info(); /* Final full version of the data */
cpumask_copy(cpu_callin_mask, cpumask_of(0));
mb();

@@ -1026,6 +1111,11 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
*/
setup_local_APIC();

+ if (x2apic_mode)
+ cpu0_logical_apicid = apic_read(APIC_LDR);
+ else
+ cpu0_logical_apicid = GET_APIC_LOGICAL_ID(apic_read(APIC_LDR));
+
/*
* Enable IO APIC before setting up error vector
*/
@@ -1214,19 +1304,6 @@ void cpu_disable_common(void)

int native_cpu_disable(void)
{
- int cpu = smp_processor_id();
-
- /*
- * Perhaps use cpufreq to drop frequency, but that could go
- * into generic code.
- *
- * We won't take down the boot processor on i386 due to some
- * interrupts only being able to be serviced by the BSP.
- * Especially so if we're not using an IOAPIC -zwane
- */
- if (cpu == 0)
- return -EBUSY;
-
clear_local_APIC();

cpu_disable_common();
@@ -1266,6 +1343,14 @@ void play_dead_common(void)
local_irq_disable();
}

+static bool wakeup_cpu0(void)
+{
+ if (smp_processor_id() == 0 && enable_start_cpu0)
+ return true;
+
+ return false;
+}
+
/*
* We need to flush the caches before going to sleep, lest we have
* dirty data in our caches when we come back up.
@@ -1329,6 +1414,11 @@ static inline void mwait_play_dead(void)
__monitor(mwait_ptr, 0, 0);
mb();
__mwait(eax, 0);
+ /*
+ * If NMI wants to wake up CPU0, start CPU0.
+ */
+ if (wakeup_cpu0())
+ start_cpu0();
}
}

@@ -1339,6 +1429,11 @@ static inline void hlt_play_dead(void)

while (1) {
native_halt();
+ /*
+ * If NMI wants to wake up CPU0, start CPU0.
+ */
+ if (wakeup_cpu0())
+ start_cpu0();
}
}

diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 76ee977..6e60b5f 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -30,23 +30,110 @@
#include <linux/mmzone.h>
#include <linux/init.h>
#include <linux/smp.h>
+#include <linux/irq.h>
#include <asm/cpu.h>

static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);

#ifdef CONFIG_HOTPLUG_CPU
+
+#ifdef CONFIG_BOOTPARAM_HOTPLUG_CPU0
+static int cpu0_hotpluggable = 1;
+#else
+static int cpu0_hotpluggable;
+static int __init enable_cpu0_hotplug(char *str)
+{
+ cpu0_hotpluggable = 1;
+ return 1;
+}
+
+__setup("cpu0_hotplug", enable_cpu0_hotplug);
+#endif
+
+#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
+/*
+ * This function offlines a CPU as early as possible and allows userspace to
+ * boot up without the CPU. The CPU can be onlined back by user after boot.
+ *
+ * This is only called for debugging CPU offline/online feature.
+ */
+int __ref _debug_hotplug_cpu(int cpu, int action)
+{
+ struct device *dev = get_cpu_device(cpu);
+ int ret;
+
+ if (!cpu_is_hotpluggable(cpu))
+ return -EINVAL;
+
+ cpu_hotplug_driver_lock();
+
+ switch (action) {
+ case 0:
+ ret = cpu_down(cpu);
+ if (!ret) {
+ pr_info("CPU %u is now offline\n", cpu);
+ kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
+ } else
+ pr_debug("Can't offline CPU%d.\n", cpu);
+ break;
+ case 1:
+ ret = cpu_up(cpu);
+ if (!ret)
+ kobject_uevent(&dev->kobj, KOBJ_ONLINE);
+ else
+ pr_debug("Can't online CPU%d.\n", cpu);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ cpu_hotplug_driver_unlock();
+
+ return ret;
+}
+
+static int __init debug_hotplug_cpu(void)
+{
+ _debug_hotplug_cpu(0, 0);
+ return 0;
+}
+
+late_initcall_sync(debug_hotplug_cpu);
+#endif /* CONFIG_DEBUG_HOTPLUG_CPU0 */
+
int __ref arch_register_cpu(int num)
{
+ struct cpuinfo_x86 *c = &cpu_data(num);
+
+ /*
+ * Currently CPU0 is only hotpluggable on Intel platforms. Other
+ * vendors can add hotplug support later.
+ */
+ if (c->x86_vendor != X86_VENDOR_INTEL)
+ cpu0_hotpluggable = 0;
+
/*
- * CPU0 cannot be offlined due to several
- * restrictions and assumptions in kernel. This basically
- * doesn't add a control file, one cannot attempt to offline
- * BSP.
+ * Two known BSP/CPU0 dependencies: Resume from suspend/hibernate
+ * depends on BSP. PIC interrupts depend on BSP.
*
- * Also certain PCI quirks require not to enable hotplug control
- * for all CPU's.
+ * If the BSP depencies are under control, one can tell kernel to
+ * enable BSP hotplug. This basically adds a control file and
+ * one can attempt to offline BSP.
*/
- if (num)
+ if (num == 0 && cpu0_hotpluggable) {
+ unsigned int irq;
+ /*
+ * We won't take down the boot processor on i386 if some
+ * interrupts only are able to be serviced by the BSP in PIC.
+ */
+ for_each_active_irq(irq) {
+ if (!IO_APIC_IRQ(irq) && irq_has_action(irq)) {
+ cpu0_hotpluggable = 0;
+ break;
+ }
+ }
+ }
+ if (num || cpu0_hotpluggable)
per_cpu(cpu_devices, num).cpu.hotpluggable = 1;

return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index 218cdb1..120cee1 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -21,6 +21,7 @@
#include <asm/suspend.h>
#include <asm/debugreg.h>
#include <asm/fpu-internal.h> /* pcntxt_mask */
+#include <asm/cpu.h>

#ifdef CONFIG_X86_32
static struct saved_context saved_context;
@@ -237,3 +238,84 @@ void restore_processor_state(void)
#ifdef CONFIG_X86_32
EXPORT_SYMBOL(restore_processor_state);
#endif
+
+/*
+ * When bsp_check() is called in hibernate and suspend, cpu hotplug
+ * is disabled already. So it's unnessary to handle race condition between
+ * cpumask query and cpu hotplug.
+ */
+static int bsp_check(void)
+{
+ if (cpumask_first(cpu_online_mask) != 0) {
+ pr_warn("CPU0 is offline.\n");
+ return -ENODEV;
+ }
+
+ return 0;
+}
+
+static int bsp_pm_callback(struct notifier_block *nb, unsigned long action,
+ void *ptr)
+{
+ int ret = 0;
+
+ switch (action) {
+ case PM_SUSPEND_PREPARE:
+ case PM_HIBERNATION_PREPARE:
+ ret = bsp_check();
+ break;
+#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
+ case PM_RESTORE_PREPARE:
+ /*
+ * When system resumes from hibernation, online CPU0 because
+ * 1. it's required for resume and
+ * 2. the CPU was online before hibernation
+ */
+ if (!cpu_online(0))
+ _debug_hotplug_cpu(0, 1);
+ break;
+ case PM_POST_RESTORE:
+ /*
+ * When a resume really happens, this code won't be called.
+ *
+ * This code is called only when user space hibernation software
+ * prepares for snapshot device during boot time. So we just
+ * call _debug_hotplug_cpu() to restore to CPU0's state prior to
+ * preparing the snapshot device.
+ *
+ * This works for normal boot case in our CPU0 hotplug debug
+ * mode, i.e. CPU0 is offline and user mode hibernation
+ * software initializes during boot time.
+ *
+ * If CPU0 is online and user application accesses snapshot
+ * device after boot time, this will offline CPU0 and user may
+ * see different CPU0 state before and after accessing
+ * the snapshot device. But hopefully this is not a case when
+ * user debugging CPU0 hotplug. Even if users hit this case,
+ * they can easily online CPU0 back.
+ *
+ * To simplify this debug code, we only consider normal boot
+ * case. Otherwise we need to remember CPU0's state and restore
+ * to that state and resolve racy conditions etc.
+ */
+ _debug_hotplug_cpu(0, 0);
+ break;
+#endif
+ default:
+ break;
+ }
+ return notifier_from_errno(ret);
+}
+
+static int __init bsp_pm_check_init(void)
+{
+ /*
+ * Set this bsp_pm_callback as lower priority than
+ * cpu_hotplug_pm_callback. So cpu_hotplug_pm_callback will be called
+ * earlier to disable cpu hotplug before bsp online check.
+ */
+ pm_notifier(bsp_pm_callback, -INT_MAX);
+ return 0;
+}
+
+core_initcall(bsp_pm_check_init);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 42bd331..a2491a2 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -601,6 +601,11 @@ cpu_hotplug_pm_callback(struct notifier_block *nb,

static int __init cpu_hotplug_pm_sync_init(void)
{
+ /*
+ * cpu_hotplug_pm_callback has higher priority than x86
+ * bsp_pm_callback which depends on cpu_hotplug_pm_callback
+ * to disable cpu hotplug to avoid cpu hotplug race.
+ */
pm_notifier(cpu_hotplug_pm_callback, 0);
return 0;
}
--
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