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Commit 8ca22552 authored by Wanpeng Li's avatar Wanpeng Li Committed by Thomas Gleixner
Browse files

x86/apic: Prevent tracing on apic_msr_write_eoi() 



The following RCU lockdep warning led to adding irq_enter()/irq_exit() into
smp_reschedule_interrupt():

 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.
 
  do_trace_write_msr
  native_write_msr
  native_apic_msr_eoi_write
  smp_reschedule_interrupt
  reschedule_interrupt

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 sent 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.

Use the wrmsr_notrace() variant in native_apic_msr_write_eoi, annotate the
kvm variant with notrace and add a native_apic_eoi callback to the apic
structure so KVM guests are covered as well.

This allows to revert the irq_enter/irq_exit dance in
smp_reschedule_interrupt().

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Suggested-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarWanpeng Li <wanpeng.li@hotmail.com>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Cc: Mike Galbraith <efault@gmx.de>
Cc: Borislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/1478488420-5982-3-git-send-email-wanpeng.li@hotmail.com


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent b2c5ea4f

arch/x86/include/asm/apic.h

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/apic/apic.c

+1 −0
Original line number Diff line number Diff line
@@ -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;

	}

}

arch/x86/kernel/kvm.c

+2 −2
Original line number Diff line number Diff line
@@ -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)

static notrace 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)

arch/x86/kernel/smp.c

+0 −2
Original line number Diff line number Diff line
@@ -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

	 */