KVM: VMX: add module parameter to avoid trapping HLT instructions (v5)
In certain use-cases, we want to allocate guests fixed time slices where idle
guest cycles leave the machine idling. There are many approaches to achieve
this but the most direct is to simply avoid trapping the HLT instruction which
lets the guest directly execute the instruction putting the processor to sleep.
Introduce this as a module-level option for kvm-vmx.ko since if you do this
for one guest, you probably want to do it for all.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index f3693ca..c195260 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -69,6 +69,9 @@
static int __read_mostly vmm_exclusive = 1;
module_param(vmm_exclusive, bool, S_IRUGO);
+static int __read_mostly yield_on_hlt = 1;
+module_param(yield_on_hlt, bool, S_IRUGO);
+
#define KVM_GUEST_CR0_MASK_UNRESTRICTED_GUEST \
(X86_CR0_WP | X86_CR0_NE | X86_CR0_NW | X86_CR0_CD)
#define KVM_GUEST_CR0_MASK \
@@ -1009,6 +1012,17 @@
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 (!yield_on_hlt &&
+ vmcs_read32(GUEST_ACTIVITY_STATE) == GUEST_ACTIVITY_HLT)
+ vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
+}
+
static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
bool has_error_code, u32 error_code,
bool reinject)
@@ -1035,6 +1049,7 @@
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)
@@ -1419,7 +1434,7 @@
&_pin_based_exec_control) < 0)
return -EIO;
- min = CPU_BASED_HLT_EXITING |
+ min =
#ifdef CONFIG_X86_64
CPU_BASED_CR8_LOAD_EXITING |
CPU_BASED_CR8_STORE_EXITING |
@@ -1432,6 +1447,10 @@
CPU_BASED_MWAIT_EXITING |
CPU_BASED_MONITOR_EXITING |
CPU_BASED_INVLPG_EXITING;
+
+ if (yield_on_hlt)
+ min |= CPU_BASED_HLT_EXITING;
+
opt = CPU_BASED_TPR_SHADOW |
CPU_BASED_USE_MSR_BITMAPS |
CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
@@ -2728,7 +2747,7 @@
vmcs_writel(GUEST_IDTR_BASE, 0);
vmcs_write32(GUEST_IDTR_LIMIT, 0xffff);
- vmcs_write32(GUEST_ACTIVITY_STATE, 0);
+ vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
vmcs_write32(GUEST_INTERRUPTIBILITY_INFO, 0);
vmcs_write32(GUEST_PENDING_DBG_EXCEPTIONS, 0);
@@ -2821,6 +2840,7 @@
} 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)
@@ -2848,6 +2868,7 @@
}
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)