If host CPUs are dedicated to a VM, we can avoid VM exits on HLT,
reducing the wake-up latency on posted interrupts.
This reintroduces a feature that has been there at some point --
see Linux 3.4 commit 10166744b80a ("KVM: VMX: remove yield_on_hlt")
for the removal -- but with the additional ability to enable it only
for selected VMs (and supporting SVM as well).
Signed-off-by: Jan H. Schönherr <jschoenh@xxxxxxxxx>
---
Note: AMD code paths are only compile tested
---
Documentation/virtual/kvm/api.txt | 12 +++++++++++-
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/svm.c | 3 ++-
arch/x86/kvm/vmx.c | 33 +++++++++++++++++++++++++++------
arch/x86/kvm/x86.c | 5 +++++
arch/x86/kvm/x86.h | 5 +++++
include/uapi/linux/kvm.h | 1 +
7 files changed, 52 insertions(+), 8 deletions(-)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 0ee812c..c06bb41 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -4172,7 +4172,17 @@ Returns: 0 on success
This capability indicates that a guest using memory monitoring instructions
(MWAIT/MWAITX) to stop a virtual CPU will not cause a VM exit. As such, time
spent while a virtual CPU is halted in this way will then be accounted for as
-guest running time on the host (as opposed to e.g. HLT).
+guest running time on the host.
+
+7.14 KVM_CAP_X86_GUEST_HLT
+
+Architectures: x86
+Parameters: none
+Returns: 0 on success
+
+This capability indicates that a guest using HLT to stop a virtual CPU will not
+cause a VM exit. As such, time spent while a virtual CPU is halted in this way
+will then be accounted for as guest running time on the host.
8. Other capabilities.
----------------------
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f7bcfaa..3197c2d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -781,6 +781,7 @@ struct kvm_arch {
gpa_t wall_clock;
+ bool hlt_in_guest;
bool mwait_in_guest;
bool ept_identity_pagetable_done;
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index ef1b320..c135b98 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1236,7 +1236,6 @@ static void init_vmcb(struct vcpu_svm *svm)
set_intercept(svm, INTERCEPT_RDPMC);
set_intercept(svm, INTERCEPT_CPUID);
set_intercept(svm, INTERCEPT_INVD);
- set_intercept(svm, INTERCEPT_HLT);
set_intercept(svm, INTERCEPT_INVLPG);
set_intercept(svm, INTERCEPT_INVLPGA);
set_intercept(svm, INTERCEPT_IOIO_PROT);
@@ -1257,6 +1256,8 @@ static void init_vmcb(struct vcpu_svm *svm)
set_intercept(svm, INTERCEPT_MONITOR);
set_intercept(svm, INTERCEPT_MWAIT);
}
+ if (!kvm_hlt_in_guest(svm->vcpu.kvm))
+ set_intercept(svm, INTERCEPT_HLT);
control->iopm_base_pa = __sme_set(iopm_base);
control->msrpm_base_pa = __sme_set(__pa(svm->msrpm));
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a067735..1b67433 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2446,6 +2446,25 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
vmx_set_interrupt_shadow(vcpu, 0);
}
+static void vmx_set_intr_info(struct kvm_vcpu *vcpu, u32 intr)
+{
+ vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr);
+
+ /*
+ * 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 (!kvm_hlt_in_guest(vcpu->kvm) || !(intr & INTR_INFO_VALID_MASK))
+ return;
+ if (is_external_interrupt(intr) || is_nmi(intr))
+ return;
+ if (vmcs_read32(GUEST_ACTIVITY_STATE) != GUEST_ACTIVITY_HLT)
+ return;
+ vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
+}
+
static void nested_vmx_inject_exception_vmexit(struct kvm_vcpu *vcpu,
unsigned long exit_qual)
{
@@ -2540,7 +2559,7 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu)
} else
intr_info |= INTR_TYPE_HARD_EXCEPTION;
- vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
+ vmx_set_intr_info(vcpu, intr_info);
}
static bool vmx_rdtscp_supported(void)
@@ -5298,6 +5317,8 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
if (kvm_mwait_in_guest(vmx->vcpu.kvm))
exec_control &= ~(CPU_BASED_MWAIT_EXITING |
CPU_BASED_MONITOR_EXITING);
+ if (kvm_hlt_in_guest(vmx->vcpu.kvm))
+ exec_control &= ~CPU_BASED_HLT_EXITING;
return exec_control;
}
@@ -5635,7 +5656,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
setup_msrs(vmx);
- vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0); /* 22.2.1 */
+ vmx_set_intr_info(vcpu, 0); /* 22.2.1 */
if (cpu_has_vmx_tpr_shadow() && !init_event) {
vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, 0);
@@ -5729,7 +5750,7 @@ static void vmx_inject_irq(struct kvm_vcpu *vcpu)
vmx->vcpu.arch.event_exit_inst_len);
} else
intr |= INTR_TYPE_EXT_INTR;
- vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr);
+ vmx_set_intr_info(vcpu, intr);
}
static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
@@ -5758,8 +5779,8 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
return;
}
- vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
- INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
+ vmx_set_intr_info(vcpu, INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK |
+ NMI_VECTOR);
}
static bool vmx_get_nmi_mask(struct kvm_vcpu *vcpu)
@@ -9301,7 +9322,7 @@ static void vmx_cancel_injection(struct kvm_vcpu *vcpu)
VM_ENTRY_INSTRUCTION_LEN,
VM_ENTRY_EXCEPTION_ERROR_CODE);
- vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0);
+ vmx_set_intr_info(vcpu, 0);
}
static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fe6627a..f17c520 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2755,6 +2755,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_SET_BOOT_CPU_ID:
case KVM_CAP_SPLIT_IRQCHIP:
case KVM_CAP_IMMEDIATE_EXIT:
+ case KVM_CAP_X86_GUEST_HLT:
r = 1;
break;
case KVM_CAP_ADJUST_CLOCK:
@@ -4068,6 +4069,10 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
r = 0;
}
break;
+ case KVM_CAP_X86_GUEST_HLT:
+ kvm->arch.hlt_in_guest = true;
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index ed8e150..b2066aa 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -266,4 +266,9 @@ static inline bool kvm_mwait_in_guest(struct kvm *kvm)
return kvm->arch.mwait_in_guest;
}
+static inline bool kvm_hlt_in_guest(struct kvm *kvm)
+{
+ return kvm->arch.hlt_in_guest;
+}
+
#endif
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 282d7613..ff8f266 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -932,6 +932,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_HYPERV_SYNIC2 148
#define KVM_CAP_HYPERV_VP_INDEX 149
#define KVM_CAP_S390_AIS_MIGRATION 150
+#define KVM_CAP_X86_GUEST_HLT 151
#ifdef KVM_CAP_IRQ_ROUTING
--
2.3.1.dirty
