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: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Acked-by: Paolo 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: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f5aaf6c83222299691364258118b0dd41b22fac7..a5a0bcfde76a5802c0125d225ab7b5ec43ad2e7b 100644 (file)
--- 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 88c657b057e223eb0eaccdac699aa91505638129..2686894350a4974764ea6a78d3b8f08b960b456a 100644 (file)
--- 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 edbbfc854e3998a038ffd8d94173dd4a2c9dfeee..aad52f1b0f9f6fcfcb70748b0ceb6c0262d0c62a 100644 (file)
--- 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)
+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)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index c00cb64bc0a12e5f6f36c37215b05a3afd178db9..68f8cc222f255aa1cf5266e2d84d7ceeb2417977 100644 (file)
--- 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
         */