linux-kernel - [PATCH v2] x86/msr: Add write msr notrace to avoid the debug codes splash

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Date:   Mon, 17 Oct 2016 20:16:43 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Wanpeng Li <wanpeng.li@...mail.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH v2] x86/msr: Add write msr notrace to avoid the debug codes splash

 ===============================
 [ INFO: suspicious RCU usage. ]
 4.8.0+ #24 Not tainted
 -------------------------------
 ./arch/x86/include/asm/msr-trace.h:47 suspicious rcu_dereference_check() usage!

 other info that might help us debug this:

 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

As Peterz pointed out:

| 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).

This patch add write msr notrace to avoid the debug codes splash.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
v1 -> v2:
 * add write msr notrace to avoid debug codes splash instead of slowdown a very frequent interrupt

 arch/x86/include/asm/apic.h |  4 ++--
 arch/x86/include/asm/msr.h  | 15 +++++++++++++++
 arch/x86/kernel/kvm.c       |  2 +-
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f5aaf6c..d38bbe8 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -174,7 +174,7 @@ static inline void disable_local_APIC(void) { }
 static inline void lapic_update_tsc_freq(void) { }
 #endif /* !CONFIG_X86_LOCAL_APIC */
 
-#ifdef CONFIG_X86_X2APIC
+#if defined CONFIG_X86_X2APIC || defined CONFIG_KVM_GUEST
 /*
  * Make previous memory operations globally visible before
  * sending the IPI through x2apic wrmsr. We need a serializing instruction or
@@ -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)
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index b5fee97..afbb221 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -127,6 +127,21 @@ notrace static inline void native_write_msr(unsigned int msr,
 }
 
 /* Can be uninlined because referenced by paravirt */
+notrace static inline void native_write_msr_notrace(unsigned int msr,
+					    unsigned low, unsigned high)
+{
+	asm volatile("1: wrmsr\n"
+		     "2:\n"
+		     _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe)
+		     : : "c" (msr), "a"(low), "d" (high) : "memory");
+}
+
+static inline void wrmsr_notrace(unsigned msr, unsigned low, unsigned high)
+{
+	native_write_msr_notrace(msr, low, high);
+}
+
+/* Can be uninlined because referenced by paravirt */
 notrace static inline int native_write_msr_safe(unsigned int msr,
 					unsigned low, unsigned high)
 {
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index edbbfc8..61cc6a5 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -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);
+	native_apic_msr_eoi_write(APIC_EOI, APIC_EOI_ACK);
 }
 
 static void kvm_guest_cpu_init(void)
-- 
1.9.1