linux-kernel - [PATCH 08/35] KVM: x86: Harden against cpufreq

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Date:	Thu, 19 Nov 2009 15:34:44 +0200
From:	Avi Kivity <avi@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org
Subject: [PATCH 08/35] KVM: x86: Harden against cpufreq

From: Zachary Amsden <zamsden@...hat.com>

If cpufreq can't determine the CPU khz, or cpufreq is not compiled in,
we should fallback to the measured TSC khz.

Signed-off-by: Zachary Amsden <zamsden@...hat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
---
 arch/x86/kvm/x86.c |   16 ++++++++++++----
 1 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 098e7f8..3cffa2c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1348,8 +1348,12 @@ out:
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	kvm_x86_ops->vcpu_load(vcpu, cpu);
-	if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0))
-		per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu);
+	if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0)) {
+		unsigned long khz = cpufreq_quick_get(cpu);
+		if (!khz)
+			khz = tsc_khz;
+		per_cpu(cpu_tsc_khz, cpu) = khz;
+	}
 	kvm_request_guest_time_update(vcpu);
 }
 
@@ -3144,8 +3148,12 @@ static void kvm_timer_init(void)
 	if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
 		cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block,
 					  CPUFREQ_TRANSITION_NOTIFIER);
-		for_each_online_cpu(cpu)
-			per_cpu(cpu_tsc_khz, cpu) = cpufreq_get(cpu);
+		for_each_online_cpu(cpu) {
+			unsigned long khz = cpufreq_get(cpu);
+			if (!khz)
+				khz = tsc_khz;
+			per_cpu(cpu_tsc_khz, cpu) = khz;
+		}
 	} else {
 		for_each_possible_cpu(cpu)
 			per_cpu(cpu_tsc_khz, cpu) = tsc_khz;
-- 
1.6.5.2

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