linux-kernel - [KVM timekeeping 08/35] Warn about unstable TSC

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Date:	Thu, 19 Aug 2010 22:07:22 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	kvm@...r.kernel.org
Cc:	Zachary Amsden <zamsden@...hat.com>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Glauber Costa <glommer@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: [KVM timekeeping 08/35] Warn about unstable TSC

If creating an SMP guest with unstable host TSC, issue a warning

Signed-off-by: Zachary Amsden <zamsden@...hat.com>
---
 arch/x86/kvm/x86.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3420f25..5e3b10e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5457,6 +5457,10 @@ void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
 						unsigned int id)
 {
+	if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
+		printk_once(KERN_WARNING
+		"kvm: SMP vm created on host with unstable TSC; "
+		"guest TSC will not be reliable\n");
 	return kvm_x86_ops->vcpu_create(kvm, id);
 }
 
-- 
1.7.1

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