From 7700270ee3c1324c18f5b7c36ee5ba1a4165919a Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Wed, 13 Jun 2007 19:55:28 +0300 Subject: [PATCH] KVM: VMX: Ensure vcpu time stamp counter is monotonous If the time stamp counter goes backwards, a guest delay loop can become infinite. This can happen if a vcpu is migrated to another cpu, where the counter has a lower value than the first cpu. Since we're doing an IPI to the first cpu anyway, we can use that to pick up the old tsc, and use that to calculate the adjustment we need to make to the tsc offset. Signed-off-by: Avi Kivity --- drivers/kvm/vmx.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c index 0b2aace70aec..d06c3627f640 100644 --- a/drivers/kvm/vmx.c +++ b/drivers/kvm/vmx.c @@ -160,6 +160,7 @@ static void __vcpu_clear(void *arg) vmcs_clear(vcpu->vmcs); if (per_cpu(current_vmcs, cpu) == vcpu->vmcs) per_cpu(current_vmcs, cpu) = NULL; + rdtscll(vcpu->host_tsc); } static void vcpu_clear(struct kvm_vcpu *vcpu) @@ -376,6 +377,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu) { u64 phys_addr = __pa(vcpu->vmcs); int cpu; + u64 tsc_this, delta; cpu = get_cpu(); @@ -409,6 +411,13 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu) rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp); vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */ + + /* + * Make sure the time stamp counter is monotonous. + */ + rdtscll(tsc_this); + delta = vcpu->host_tsc - tsc_this; + vmcs_write64(TSC_OFFSET, vmcs_read64(TSC_OFFSET) + delta); } } -- 2.20.1