KVM: X86: Provide a capability to disable HLT intercepts

If host CPUs are dedicated to a VM, we can avoid VM exits on HLT.
This patch adds the per-VM capability to disable them.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Jan H. Schönherr <jschoenh@amazon.de>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 744a202..e9c7487 100644 (file)
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -4367,6 +4367,7 @@ Returns: 0 on success, -EINVAL when args[0] contains invalid exits
 Valid bits in args[0] are
 
 #define KVM_X86_DISABLE_EXITS_MWAIT            (1 << 0)
+#define KVM_X86_DISABLE_EXITS_HLT              (1 << 1)
 
 Enabling this capability on a VM provides userspace with a way to no
 longer intercept some instructions for improved latency in some
@@ -4375,6 +4376,7 @@ physical CPUs.  More bits can be added in the future; userspace can
 just pass the KVM_CHECK_EXTENSION result to KVM_ENABLE_CAP to disable
 all such vmexits.
 
+Do not enable KVM_FEATURE_PV_UNHALT if you disable HLT exits.
 
 8. Other capabilities.
 ----------------------

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a85b640..31f4186 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -812,6 +812,7 @@ struct kvm_arch {
        gpa_t wall_clock;
 
        bool mwait_in_guest;
+       bool hlt_in_guest;
 
        bool ept_identity_pagetable_done;
        gpa_t ept_identity_map_addr;

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index e2d3050..82055b9 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -135,6 +135,11 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
                        return -EINVAL;
        }
 
+       best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
+       if (kvm_hlt_in_guest(vcpu->kvm) && best &&
+               (best->eax & (1 << KVM_FEATURE_PV_UNHALT)))
+               best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT);
+
        /* Update physical-address width */
        vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
        kvm_mmu_reset_context(vcpu);

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f6578ce..0f801d8 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1380,7 +1380,6 @@ 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);
@@ -1403,6 +1402,9 @@ static void init_vmcb(struct vcpu_svm *svm)
                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));
        control->int_ctl = V_INTR_MASKING_MASK;

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7cef183..65747d1 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2556,6 +2556,19 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned long *exit
        return 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 (kvm_hlt_in_guest(vcpu->kvm) &&
+                       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)
 {
        struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -2586,6 +2599,8 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu)
                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)
@@ -5545,6 +5560,8 @@ 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;
 }
 
@@ -5906,6 +5923,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
        update_exception_bitmap(vcpu);
 
        vpid_sync_context(vmx->vpid);
+       if (init_event)
+               vmx_clear_hlt(vcpu);
 }
 
 /*
@@ -5976,6 +5995,8 @@ 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)
@@ -6006,6 +6027,8 @@ 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 bool vmx_get_nmi_mask(struct kvm_vcpu *vcpu)
@@ -12347,6 +12370,7 @@ static int vmx_pre_enter_smm(struct kvm_vcpu *vcpu, char *smstate)
 
        vmx->nested.smm.vmxon = vmx->nested.vmxon;
        vmx->nested.vmxon = false;
+       vmx_clear_hlt(vcpu);
        return 0;
 }
 

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index db95d4d..9e6aaf6 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2878,6 +2878,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
                r = KVM_CLOCK_TSC_STABLE;
                break;
        case KVM_CAP_X86_DISABLE_EXITS:
+               r |=  KVM_X86_DISABLE_EXITS_HTL;
                if(kvm_can_mwait_in_guest())
                        r |= KVM_X86_DISABLE_EXITS_MWAIT;
                break;
@@ -4232,6 +4233,8 @@ split_irqchip_unlock:
                if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
                        kvm_can_mwait_in_guest())
                        kvm->arch.mwait_in_guest = true;
+               if (cap->args[0] & KVM_X86_DISABLE_EXITS_HTL)
+                       kvm->arch.hlt_in_guest = true;
                r = 0;
                break;
        default:

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 026b239..6d14589 100644 (file)
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -265,11 +265,18 @@ static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
         })
 
 #define KVM_X86_DISABLE_EXITS_MWAIT          (1 << 0)
-#define KVM_X86_DISABLE_VALID_EXITS          (KVM_X86_DISABLE_EXITS_MWAIT)
+#define KVM_X86_DISABLE_EXITS_HTL            (1 << 1)
+#define KVM_X86_DISABLE_VALID_EXITS          (KVM_X86_DISABLE_EXITS_MWAIT | \
+                                              KVM_X86_DISABLE_EXITS_HTL)
 
 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