[PATCH v6 2/2] x86/apic: x2apic write eoi msr notrace

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

| RCU used illegally from idle CPU!
| rcu_scheduler_active = 1, debug_locks = 0
| RCU used illegally from extended quiescent state!
| no locks held by swapper/1/0.
| 
|  [<ffffffff9d492b95>] do_trace_write_msr+0x135/0x140
|  [<ffffffff9d06f860>] native_write_msr+0x20/0x30
|  [<ffffffff9d065fad>] native_apic_msr_eoi_write+0x1d/0x30
|  [<ffffffff9d05bd1d>] smp_reschedule_interrupt+0x1d/0x30
|  [<ffffffff9d8daec6>] reschedule_interrupt+0x96/0xa0

Reschedule interrupt may be called in cpu idle state. This causes lockdep
check warning above.

As Peterz pointed out:

| So now we're making a very frequent interrupt slower because of debug 
| code.
|
| The thing is, many many smp_reschedule_interrupt() invocations don't
| actually execute anything much at all and are only send to tickle the
| return to user path (which does the actual preemption).
| 
| Having to do the whole irq_enter/irq_exit dance just for this unlikely
| debug case totally blows.

This patch converts x2apic write eoi msr to notrace to avoid the debug 
codes splash and reverts irq_enter/irq_exit dance to avoid to make a very 
frequent interrupt slower because of debug code.

Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
 arch/x86/include/asm/apic.h | 3 ++-
 arch/x86/kernel/apic/apic.c | 1 +
 arch/x86/kernel/kvm.c       | 4 ++--
 arch/x86/kernel/smp.c       | 2 --
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f5aaf6c..a5a0bcf 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -196,7 +196,7 @@ static inline void native_apic_msr_write(u32 reg, u32 v)
 
 static inline void native_apic_msr_eoi_write(u32 reg, u32 v)
 {
-	wrmsr(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
+	wrmsr_notrace(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
 }
 
 static inline u32 native_apic_msr_read(u32 reg)
@@ -332,6 +332,7 @@ struct apic {
 	 * on write for EOI.
 	 */
 	void (*eoi_write)(u32 reg, u32 v);
+	void (*native_eoi_write)(u32 reg, u32 v);
 	u64 (*icr_read)(void);
 	void (*icr_write)(u32 low, u32 high);
 	void (*wait_icr_idle)(void);
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 88c657b..2686894 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2263,6 +2263,7 @@ void __init apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v))
 	for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) {
 		/* Should happen once for each apic */
 		WARN_ON((*drv)->eoi_write == eoi_write);
+		(*drv)->native_eoi_write = (*drv)->eoi_write;
 		(*drv)->eoi_write = eoi_write;
 	}
 }
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index edbbfc8..d230513 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -308,7 +308,7 @@ static void kvm_register_steal_time(void)
 
 static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
 
-static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
+notrace static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 {
 	/**
 	 * This relies on __test_and_clear_bit to modify the memory
@@ -319,7 +319,7 @@ static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 	 */
 	if (__test_and_clear_bit(KVM_PV_EOI_BIT, this_cpu_ptr(&kvm_apic_eoi)))
 		return;
-	apic_write(APIC_EOI, APIC_EOI_ACK);
+	apic->native_eoi_write(APIC_EOI, APIC_EOI_ACK);
 }
 
 static void kvm_guest_cpu_init(void)
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index c00cb64..68f8cc2 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -261,10 +261,8 @@ static inline void __smp_reschedule_interrupt(void)
 
 __visible void smp_reschedule_interrupt(struct pt_regs *regs)
 {
-	irq_enter();
 	ack_APIC_irq();
 	__smp_reschedule_interrupt();
-	irq_exit();
 	/*
 	 * KVM uses this interrupt to force a cpu out of guest mode
 	 */
-- 
1.9.1