linux-kernel - [PATCH v3 05/16] KVM: x86: tone down WARN_ON pit.state

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Date:	Wed,  2 Mar 2016 22:56:42 +0100
From:	Radim Krčmář <radimkrcmar@....cz>
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 v3 05/16] KVM: x86: tone down WARN_ON pit.state_lock

From: Radim Krčmář <rkrcmar@...hat.com>

If the guest could hit this, it would hang the host kernel, bacause 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>
---
 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 0f5655c50e0c..e5a3e8015e30 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);
-- 
2.7.2