2 files changed, 52 insertions, 12 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1d6c3f757cb6..82129437e873 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -358,6 +358,7 @@ struct kvm_vcpu_arch {
         unsigned int time_offset;
         struct page *time_page;
 
+        bool singlestep; /* guest is single stepped by KVM */
         bool nmi_pending;
         bool nmi_injected;
 
@@ -771,6 +772,7 @@ enum {
 #define HF_HIF_MASK             (1 << 1)
 #define HF_VINTR_MASK           (1 << 2)
 #define HF_NMI_MASK             (1 << 3)
+#define HF_IRET_MASK            (1 << 4)
 
 /*
  * Hardware virtualization extension instructions may fault if a
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 377c4f17d170..71510e07e69e 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -965,15 +965,16 @@ static void svm_set_segment(struct kvm_vcpu *vcpu,
 
 }
 
-static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
+static void update_db_intercept(struct kvm_vcpu *vcpu)
 {
-        int old_debug = vcpu->guest_debug;
         struct vcpu_svm *svm = to_svm(vcpu);
 
-        vcpu->guest_debug = dbg->control;
-
         svm->vmcb->control.intercept_exceptions &=
                 ~((1 << DB_VECTOR) | (1 << BP_VECTOR));
+
+        if (vcpu->arch.singlestep)
+                svm->vmcb->control.intercept_exceptions |= (1 << DB_VECTOR);
+
         if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {
                 if (vcpu->guest_debug &
                     (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
@@ -984,6 +985,16 @@ static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
                                 1 << BP_VECTOR;
         } else
                 vcpu->guest_debug = 0;
+}
+
+static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
+{
+        int old_debug = vcpu->guest_debug;
+        struct vcpu_svm *svm = to_svm(vcpu);
+
+        vcpu->guest_debug = dbg->control;
+
+        update_db_intercept(vcpu);
 
         if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
                 svm->vmcb->save.dr7 = dbg->arch.debugreg[7];
@@ -1133,14 +1144,30 @@ static int pf_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 static int db_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 {
         if (!(svm->vcpu.guest_debug &
-              (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))) {
+              (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)) &&
+                !svm->vcpu.arch.singlestep) {
                 kvm_queue_exception(&svm->vcpu, DB_VECTOR);
                 return 1;
         }
-        kvm_run->exit_reason = KVM_EXIT_DEBUG;
-        kvm_run->debug.arch.pc = svm->vmcb->save.cs.base + svm->vmcb->save.rip;
-        kvm_run->debug.arch.exception = DB_VECTOR;
-        return 0;
+
+        if (svm->vcpu.arch.singlestep) {
+                svm->vcpu.arch.singlestep = false;
+                if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP))
+                        svm->vmcb->save.rflags &=
+                                ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
+                update_db_intercept(&svm->vcpu);
+        }
+
+        if (svm->vcpu.guest_debug &
+            (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)){
+                kvm_run->exit_reason = KVM_EXIT_DEBUG;
+                kvm_run->debug.arch.pc =
+                        svm->vmcb->save.cs.base + svm->vmcb->save.rip;
+                kvm_run->debug.arch.exception = DB_VECTOR;
+                return 0;
+        }
+
+        return 1;
 }
 
 static int bp_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
@@ -1887,7 +1914,7 @@ static int iret_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 {
         ++svm->vcpu.stat.nmi_window_exits;
         svm->vmcb->control.intercept &= ~(1UL << INTERCEPT_IRET);
-        svm->vcpu.arch.hflags &= ~HF_NMI_MASK;
+        svm->vcpu.arch.hflags |= HF_IRET_MASK;
         return 1;
 }
 
@@ -2357,8 +2384,16 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
 {
         struct vcpu_svm *svm = to_svm(vcpu);
 
-        if (svm->vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK)
-                enable_irq_window(vcpu);
+        if ((svm->vcpu.arch.hflags & (HF_NMI_MASK | HF_IRET_MASK))
+            == HF_NMI_MASK)
+                return; /* IRET will cause a vm exit */
+
+        /* Something prevents NMI from been injected. Single step over
+           possible problem (IRET or exception injection or interrupt
+           shadow) */
+        vcpu->arch.singlestep = true;
+        svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
+        update_db_intercept(vcpu);
 }
 
 static int svm_set_tss_addr(struct kvm *kvm, unsigned int addr)
@@ -2401,6 +2436,9 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)
         int type;
         u32 exitintinfo = svm->vmcb->control.exit_int_info;
 
+        if (svm->vcpu.arch.hflags & HF_IRET_MASK)
+                svm->vcpu.arch.hflags &= ~(HF_NMI_MASK | HF_IRET_MASK);
+
         svm->vcpu.arch.nmi_injected = false;
         kvm_clear_exception_queue(&svm->vcpu);
         kvm_clear_interrupt_queue(&svm->vcpu);