[RFC PATCH 11/18] KVM: no exiting from guest when slave CPU halted

Tomoki Sekiyama
2012-06-28T06:08:17Z

Avoid exiting from a guest on slave CPU even if HLT instruction is
executed. Since the slave CPU is dedicated to a vCPU, exit on HLT is
not required, and avoiding VM exit will improve the guest's performance.

This is a partial revert of

10166744b80a ("KVM: VMX: remove yield_on_hlt")

Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---

arch/x86/kvm/vmx.c | 22 +++++++++++++++++++++-
1 files changed, 21 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e24392c..f0c6532 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1688,6 +1688,17 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
vmx_set_interrupt_shadow(vcpu, 0);
}

+static void vmx_clear_hlt(struct kvm_vcpu *vcpu)
+{
+ /* Ensure that we clear the HLT state in the VMCS. We don't need to
+ * explicitly skip the instruction because if the HLT state is set, then
+ * the instruction is already executing and RIP has already been
+ * advanced. */
+ if (vcpu->arch.slave_cpu >= 0 &&
+ vmcs_read32(GUEST_ACTIVITY_STATE) == GUEST_ACTIVITY_HLT)
+ vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
+}
+
/*
* KVM wants to inject page-faults which it got to the guest. This function
* checks whether in a nested guest, we need to inject them to L1 or L2.
@@ -1740,6 +1751,7 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
intr_info |= INTR_TYPE_HARD_EXCEPTION;

vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
+ vmx_clear_hlt(vcpu);
}

static bool vmx_rdtscp_supported(void)
@@ -4045,6 +4057,7 @@ static void vmx_inject_irq(struct kvm_vcpu *vcpu)
} else
intr |= INTR_TYPE_EXT_INTR;
vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr);
+ vmx_clear_hlt(vcpu);
}

static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
@@ -4076,6 +4089,7 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
}
vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
+ vmx_clear_hlt(vcpu);
}

static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)
@@ -7137,7 +7151,13 @@ static int vmx_check_intercept(struct kvm_vcpu *vcpu,

static void vmx_set_slave_mode(struct kvm_vcpu *vcpu, bool slave)
{
- /* Nothing */
+ if (slave) {
+ vmcs_clear_bits(CPU_BASED_VM_EXEC_CONTROL,
+ CPU_BASED_HLT_EXITING);
+ } else {
+ vmcs_set_bits(CPU_BASED_VM_EXEC_CONTROL,
+ CPU_BASED_HLT_EXITING);
+ }
}

static struct kvm_x86_ops vmx_x86_ops = {