linux-kernel - [PATCH v2 05/14] KVM: x86: tone down WARN_ON pit.state

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Date:	Wed, 17 Feb 2016 20:14:47 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Yuki Shibuya <shibuya.yk@...s.nec.co.jp>
Subject: [PATCH v2 05/14] KVM: x86: tone down WARN_ON pit.state_lock

A guest could hang the host kernel if it could hit the WARN_ON, because
of sheer number of those reports.  Internal callers have to be sensible
anyway, so we now only check for it in an API function.

Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
---
 v2: new

 arch/x86/kvm/i8254.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index cbb911728ac8..328b21f3ab7c 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -76,8 +76,6 @@ static void pit_set_gate(struct kvm *kvm, int channel, u32 val)
 	struct kvm_kpit_channel_state *c =
 		&kvm->arch.vpit->pit_state.channels[channel];
 
-	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
-
 	switch (c->mode) {
 	default:
 	case 0:
@@ -99,8 +97,6 @@ static void pit_set_gate(struct kvm *kvm, int channel, u32 val)
 
 static int pit_get_gate(struct kvm *kvm, int channel)
 {
-	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
-
 	return kvm->arch.vpit->pit_state.channels[channel].gate;
 }
 
@@ -144,8 +140,6 @@ static int pit_get_count(struct kvm *kvm, int channel)
 	s64 d, t;
 	int counter;
 
-	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
-
 	t = kpit_elapsed(kvm, c, channel);
 	d = muldiv64(t, KVM_PIT_FREQ, NSEC_PER_SEC);
 
@@ -174,8 +168,6 @@ static int pit_get_out(struct kvm *kvm, int channel)
 	s64 d, t;
 	int out;
 
-	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
-
 	t = kpit_elapsed(kvm, c, channel);
 	d = muldiv64(t, KVM_PIT_FREQ, NSEC_PER_SEC);
 
@@ -207,8 +199,6 @@ static void pit_latch_count(struct kvm *kvm, int channel)
 	struct kvm_kpit_channel_state *c =
 		&kvm->arch.vpit->pit_state.channels[channel];
 
-	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
-
 	if (!c->count_latched) {
 		c->latched_count = pit_get_count(kvm, channel);
 		c->count_latched = c->rw_mode;
@@ -220,8 +210,6 @@ static void pit_latch_status(struct kvm *kvm, int channel)
 	struct kvm_kpit_channel_state *c =
 		&kvm->arch.vpit->pit_state.channels[channel];
 
-	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
-
 	if (!c->status_latched) {
 		/* TODO: Return NULL COUNT (bit 6). */
 		c->status = ((pit_get_out(kvm, channel) << 7) |
@@ -367,8 +355,6 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
 {
 	struct kvm_kpit_state *ps = &kvm->arch.vpit->pit_state;
 
-	WARN_ON(!mutex_is_locked(&ps->lock));
-
 	pr_debug("load_count val is %d, channel is %d\n", val, channel);
 
 	/*
@@ -406,6 +392,9 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
 void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val, int hpet_legacy_start)
 {
 	u8 saved_mode;
+
+	WARN_ON_ONCE(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
+
 	if (hpet_legacy_start) {
 		/* save existing mode for later reenablement */
 		WARN_ON(channel != 0);
-- 
2.7.1