[v2,4/5] KVM: x86: Add kvm_skip_emulated_instruction and use it.

Commit Message

Kyle Huey Nov. 29, 2016, 8:40 p.m. UTC

kvm_skip_emulated_instruction calls both
kvm_x86_ops->skip_emulated_instruction and kvm_vcpu_check_singlestep,
skipping the emulated instruction and generating a trap if necessary.

Replacing skip_emulated_instruction calls with
kvm_skip_emulated_instruction is straightforward, except for:

- ICEBP, which is already inside a trap, so avoid triggering another trap.
- Instructions that can trigger exits to userspace, such as the IO insns,
  MOVs to CR8, and HALT. If kvm_skip_emulated_instruction does trigger a
  KVM_GUESTDBG_SINGLESTEP exit, and the handling code for
  IN/OUT/MOV CR8/HALT also triggers an exit to userspace, the latter will
  take precedence. The singlestep will be triggered again on the next
  instruction, which is the current behavior.
- Task switch instructions which would require additional handling (e.g.
  the task switch bit) and are instead left alone.
- Cases where VMLAUNCH/VMRESUME do not proceed to the next instruction,
  which do not trigger singlestep traps as mentioned previously.

Signed-off-by: Kyle Huey <[e-mail]>
---
 arch/x86/include/asm/kvm_host.h |   3 +-
 arch/x86/kvm/cpuid.c            |   3 +-
 arch/x86/kvm/svm.c              |  11 +--
 arch/x86/kvm/vmx.c              | 177 ++++++++++++++++------------------------
 arch/x86/kvm/x86.c              |  33 ++++++--
 5 files changed, 103 insertions(+), 124 deletions(-)

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 80bad5c..8d15870 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1363,17 +1363,18 @@  void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
 				     struct kvm_async_pf *work);
 void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
 				 struct kvm_async_pf *work);
 void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu,
 			       struct kvm_async_pf *work);
 bool kvm_arch_can_inject_async_page_present(struct kvm_vcpu *vcpu);
 extern bool kvm_find_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
 
-void kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err);
+int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu);
+int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err);
 
 int kvm_is_in_guest(void);
 
 int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size);
 int x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size);
 bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu);
 bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu);
 
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 07cc629..dc2685e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -885,12 +885,11 @@  int kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
 
 	eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
 	ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
 	kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx);
 	kvm_register_write(vcpu, VCPU_REGS_RAX, eax);
 	kvm_register_write(vcpu, VCPU_REGS_RBX, ebx);
 	kvm_register_write(vcpu, VCPU_REGS_RCX, ecx);
 	kvm_register_write(vcpu, VCPU_REGS_RDX, edx);
-	kvm_x86_ops->skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_cpuid);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5bdffcd..08a4d3a 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3146,18 +3146,17 @@  static int skinit_interception(struct vcpu_svm *svm)
 	trace_kvm_skinit(svm->vmcb->save.rip, kvm_register_read(&svm->vcpu, VCPU_REGS_RAX));
 
 	kvm_queue_exception(&svm->vcpu, UD_VECTOR);
 	return 1;
 }
 
 static int wbinvd_interception(struct vcpu_svm *svm)
 {
-	kvm_emulate_wbinvd(&svm->vcpu);
-	return 1;
+	return kvm_emulate_wbinvd(&svm->vcpu);
 }
 
 static int xsetbv_interception(struct vcpu_svm *svm)
 {
 	u64 new_bv = kvm_read_edx_eax(&svm->vcpu);
 	u32 index = kvm_register_read(&svm->vcpu, VCPU_REGS_RCX);
 
 	if (kvm_set_xcr(&svm->vcpu, index, new_bv) == 0) {
@@ -3270,19 +3269,17 @@  static int emulate_on_interception(struct vcpu_svm *svm)
 static int rdpmc_interception(struct vcpu_svm *svm)
 {
 	int err;
 
 	if (!static_cpu_has(X86_FEATURE_NRIPS))
 		return emulate_on_interception(svm);
 
 	err = kvm_rdpmc(&svm->vcpu);
-	kvm_complete_insn_gp(&svm->vcpu, err);
-
-	return 1;
+	return kvm_complete_insn_gp(&svm->vcpu, err);
 }
 
 static bool check_selective_cr0_intercepted(struct vcpu_svm *svm,
 					    unsigned long val)
 {
 	unsigned long cr0 = svm->vcpu.arch.cr0;
 	bool ret = false;
 	u64 intercept;
@@ -3369,19 +3366,17 @@  static int cr_interception(struct vcpu_svm *svm)
 			break;
 		default:
 			WARN(1, "unhandled read from CR%d", cr);
 			kvm_queue_exception(&svm->vcpu, UD_VECTOR);
 			return 1;
 		}
 		kvm_register_write(&svm->vcpu, reg, val);
 	}
-	kvm_complete_insn_gp(&svm->vcpu, err);
-
-	return 1;
+	return kvm_complete_insn_gp(&svm->vcpu, err);
 }
 
 static int dr_interception(struct vcpu_svm *svm)
 {
 	int reg, dr;
 	unsigned long val;
 
 	if (svm->vcpu.guest_debug == 0) {
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index f4f6304..16a144d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5551,33 +5551,38 @@  static int handle_triple_fault(struct kvm_vcpu *vcpu)
 {
 	vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
 	return 0;
 }
 
 static int handle_io(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification;
-	int size, in, string;
+	int size, in, string, ret;
 	unsigned port;
 
 	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 	string = (exit_qualification & 16) != 0;
 	in = (exit_qualification & 8) != 0;
 
 	++vcpu->stat.io_exits;
 
 	if (string || in)
 		return emulate_instruction(vcpu, 0) == EMULATE_DONE;
 
 	port = exit_qualification >> 16;
 	size = (exit_qualification & 7) + 1;
-	skip_emulated_instruction(vcpu);
 
-	return kvm_fast_pio_out(vcpu, size, port);
+	ret = kvm_skip_emulated_instruction(vcpu);
+
+	/*
+	 * TODO: we might be squashing a KVM_GUESTDBG_SINGLESTEP-triggered
+	 * KVM_EXIT_DEBUG here.
+	 */
+	return kvm_fast_pio_out(vcpu, size, port) && ret;
 }
 
 static void
 vmx_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
 {
 	/*
 	 * Patch in the VMCALL instruction:
 	 */
@@ -5665,80 +5670,79 @@  static void handle_clts(struct kvm_vcpu *vcpu)
 }
 
 static int handle_cr(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification, val;
 	int cr;
 	int reg;
 	int err;
+	int ret;
 
 	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 	cr = exit_qualification & 15;
 	reg = (exit_qualification >> 8) & 15;
 	switch ((exit_qualification >> 4) & 3) {
 	case 0: /* mov to cr */
 		val = kvm_register_readl(vcpu, reg);
 		trace_kvm_cr_write(cr, val);
 		switch (cr) {
 		case 0:
 			err = handle_set_cr0(vcpu, val);
-			kvm_complete_insn_gp(vcpu, err);
-			return 1;
+			return kvm_complete_insn_gp(vcpu, err);
 		case 3:
 			err = kvm_set_cr3(vcpu, val);
-			kvm_complete_insn_gp(vcpu, err);
-			return 1;
+			return kvm_complete_insn_gp(vcpu, err);
 		case 4:
 			err = handle_set_cr4(vcpu, val);
-			kvm_complete_insn_gp(vcpu, err);
-			return 1;
+			return kvm_complete_insn_gp(vcpu, err);
 		case 8: {
 				u8 cr8_prev = kvm_get_cr8(vcpu);
 				u8 cr8 = (u8)val;
 				err = kvm_set_cr8(vcpu, cr8);
-				kvm_complete_insn_gp(vcpu, err);
+				ret = kvm_complete_insn_gp(vcpu, err);
 				if (lapic_in_kernel(vcpu))
-					return 1;
+					return ret;
 				if (cr8_prev <= cr8)
-					return 1;
+					return ret;
+				/*
+				 * TODO: we might be squashing a
+				 * KVM_GUESTDBG_SINGLESTEP-triggered
+				 * KVM_EXIT_DEBUG here.
+				 */
 				vcpu->run->exit_reason = KVM_EXIT_SET_TPR;
 				return 0;
 			}
 		}
 		break;
 	case 2: /* clts */
 		handle_clts(vcpu);
 		trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
 		vmx_fpu_activate(vcpu);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	case 1: /*mov from cr*/
 		switch (cr) {
 		case 3:
 			val = kvm_read_cr3(vcpu);
 			kvm_register_write(vcpu, reg, val);
 			trace_kvm_cr_read(cr, val);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		case 8:
 			val = kvm_get_cr8(vcpu);
 			kvm_register_write(vcpu, reg, val);
 			trace_kvm_cr_read(cr, val);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 		break;
 	case 3: /* lmsw */
 		val = (exit_qualification >> LMSW_SOURCE_DATA_SHIFT) & 0x0f;
 		trace_kvm_cr_write(0, (kvm_read_cr0(vcpu) & ~0xful) | val);
 		kvm_lmsw(vcpu, val);
 
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	default:
 		break;
 	}
 	vcpu->run->exit_reason = 0;
 	vcpu_unimpl(vcpu, "unhandled control register: op %d cr %d\n",
 	       (int)(exit_qualification >> 4) & 3, cr);
 	return 0;
 }
@@ -5799,18 +5803,17 @@  static int handle_dr(struct kvm_vcpu *vcpu)
 
 		if (kvm_get_dr(vcpu, dr, &val))
 			return 1;
 		kvm_register_write(vcpu, reg, val);
 	} else
 		if (kvm_set_dr(vcpu, dr, kvm_register_readl(vcpu, reg)))
 			return 1;
 
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static u64 vmx_get_dr6(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.dr6;
 }
 
 static void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val)
@@ -5853,18 +5856,17 @@  static int handle_rdmsr(struct kvm_vcpu *vcpu)
 		return 1;
 	}
 
 	trace_kvm_msr_read(ecx, msr_info.data);
 
 	/* FIXME: handling of bits 32:63 of rax, rdx */
 	vcpu->arch.regs[VCPU_REGS_RAX] = msr_info.data & -1u;
 	vcpu->arch.regs[VCPU_REGS_RDX] = (msr_info.data >> 32) & -1u;
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_wrmsr(struct kvm_vcpu *vcpu)
 {
 	struct msr_data msr;
 	u32 ecx = vcpu->arch.regs[VCPU_REGS_RCX];
 	u64 data = (vcpu->arch.regs[VCPU_REGS_RAX] & -1u)
 		| ((u64)(vcpu->arch.regs[VCPU_REGS_RDX] & -1u) << 32);
@@ -5874,18 +5876,17 @@  static int handle_wrmsr(struct kvm_vcpu *vcpu)
 	msr.host_initiated = false;
 	if (kvm_set_msr(vcpu, &msr) != 0) {
 		trace_kvm_msr_write_ex(ecx, data);
 		kvm_inject_gp(vcpu, 0);
 		return 1;
 	}
 
 	trace_kvm_msr_write(ecx, data);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_tpr_below_threshold(struct kvm_vcpu *vcpu)
 {
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
 	return 1;
 }
 
@@ -5919,56 +5920,52 @@  static int handle_invd(struct kvm_vcpu *vcpu)
 	return emulate_instruction(vcpu, 0) == EMULATE_DONE;
 }
 
 static int handle_invlpg(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 
 	kvm_mmu_invlpg(vcpu, exit_qualification);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_rdpmc(struct kvm_vcpu *vcpu)
 {
 	int err;
 
 	err = kvm_rdpmc(vcpu);
-	kvm_complete_insn_gp(vcpu, err);
-
-	return 1;
+	return kvm_complete_insn_gp(vcpu, err);
 }
 
 static int handle_wbinvd(struct kvm_vcpu *vcpu)
 {
-	kvm_emulate_wbinvd(vcpu);
-	return 1;
+	return kvm_emulate_wbinvd(vcpu);
 }
 
 static int handle_xsetbv(struct kvm_vcpu *vcpu)
 {
 	u64 new_bv = kvm_read_edx_eax(vcpu);
 	u32 index = kvm_register_read(vcpu, VCPU_REGS_RCX);
 
 	if (kvm_set_xcr(vcpu, index, new_bv) == 0)
-		skip_emulated_instruction(vcpu);
+		return kvm_skip_emulated_instruction(vcpu);
 	return 1;
 }
 
 static int handle_xsaves(struct kvm_vcpu *vcpu)
 {
-	skip_emulated_instruction(vcpu);
+	kvm_skip_emulated_instruction(vcpu);
 	WARN(1, "this should never happen\n");
 	return 1;
 }
 
 static int handle_xrstors(struct kvm_vcpu *vcpu)
 {
-	skip_emulated_instruction(vcpu);
+	kvm_skip_emulated_instruction(vcpu);
 	WARN(1, "this should never happen\n");
 	return 1;
 }
 
 static int handle_apic_access(struct kvm_vcpu *vcpu)
 {
 	if (likely(fasteoi)) {
 		unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
@@ -5979,18 +5976,17 @@  static int handle_apic_access(struct kvm_vcpu *vcpu)
 		/*
 		 * Sane guest uses MOV to write EOI, with written value
 		 * not cared. So make a short-circuit here by avoiding
 		 * heavy instruction emulation.
 		 */
 		if ((access_type == TYPE_LINEAR_APIC_INST_WRITE) &&
 		    (offset == APIC_EOI)) {
 			kvm_lapic_set_eoi(vcpu);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 	}
 	return emulate_instruction(vcpu, 0) == EMULATE_DONE;
 }
 
 static int handle_apic_eoi_induced(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
@@ -6129,18 +6125,17 @@  static int handle_ept_violation(struct kvm_vcpu *vcpu)
 static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
 {
 	int ret;
 	gpa_t gpa;
 
 	gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
 	if (!kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
 		trace_kvm_fast_mmio(gpa);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	ret = handle_mmio_page_fault(vcpu, gpa, true);
 	if (likely(ret == RET_MMIO_PF_EMULATE))
 		return x86_emulate_instruction(vcpu, gpa, 0, NULL, 0) ==
 					      EMULATE_DONE;
 
 	if (unlikely(ret == RET_MMIO_PF_INVALID))
@@ -6503,25 +6498,22 @@  static __exit void hardware_unsetup(void)
  * exiting, so only get here on cpu with PAUSE-Loop-Exiting.
  */
 static int handle_pause(struct kvm_vcpu *vcpu)
 {
 	if (ple_gap)
 		grow_ple_window(vcpu);
 
 	kvm_vcpu_on_spin(vcpu);
-	skip_emulated_instruction(vcpu);
-
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_nop(struct kvm_vcpu *vcpu)
 {
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_mwait(struct kvm_vcpu *vcpu)
 {
 	printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
 	return handle_nop(vcpu);
 }
 
@@ -6818,59 +6810,53 @@  static int nested_vmx_check_vmptr(struct kvm_vcpu *vcpu, int exit_reason,
 		 *
 		 * Note - IA32_VMX_BASIC[48] will never be 1
 		 * for the nested case;
 		 * which replaces physical address width with 32
 		 *
 		 */
 		if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
 			nested_vmx_failInvalid(vcpu);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 
 		page = nested_get_page(vcpu, vmptr);
 		if (page == NULL ||
 		    *(u32 *)kmap(page) != VMCS12_REVISION) {
 			nested_vmx_failInvalid(vcpu);
 			kunmap(page);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 		kunmap(page);
 		vmx->nested.vmxon_ptr = vmptr;
 		break;
 	case EXIT_REASON_VMCLEAR:
 		if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMCLEAR_INVALID_ADDRESS);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 
 		if (vmptr == vmx->nested.vmxon_ptr) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMCLEAR_VMXON_POINTER);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 		break;
 	case EXIT_REASON_VMPTRLD:
 		if (!PAGE_ALIGNED(vmptr) || (vmptr >> maxphyaddr)) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMPTRLD_INVALID_ADDRESS);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 
 		if (vmptr == vmx->nested.vmxon_ptr) {
 			nested_vmx_failValid(vcpu,
 					     VMXERR_VMCLEAR_VMXON_POINTER);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 		break;
 	default:
 		return 1; /* shouldn't happen */
 	}
 
 	if (vmpointer)
 		*vmpointer = vmptr;
@@ -6916,18 +6902,17 @@  static int handle_vmon(struct kvm_vcpu *vcpu)
 		return 1;
 	}
 
 	if (nested_vmx_check_vmptr(vcpu, EXIT_REASON_VMON, NULL))
 		return 1;
 
 	if (vmx->nested.vmxon) {
 		nested_vmx_failValid(vcpu, VMXERR_VMXON_IN_VMX_ROOT_OPERATION);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	if ((vmx->msr_ia32_feature_control & VMXON_NEEDED_FEATURES)
 			!= VMXON_NEEDED_FEATURES) {
 		kvm_inject_gp(vcpu, 0);
 		return 1;
 	}
 
@@ -6958,18 +6943,17 @@  static int handle_vmon(struct kvm_vcpu *vcpu)
 
 	hrtimer_init(&vmx->nested.preemption_timer, CLOCK_MONOTONIC,
 		     HRTIMER_MODE_REL_PINNED);
 	vmx->nested.preemption_timer.function = vmx_preemption_timer_fn;
 
 	vmx->nested.vmxon = true;
 
 	nested_vmx_succeed(vcpu);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 
 out_shadow_vmcs:
 	kfree(vmx->nested.cached_vmcs12);
 
 out_cached_vmcs12:
 	free_page((unsigned long)vmx->nested.msr_bitmap);
 
 out_msr_bitmap:
@@ -7079,18 +7063,17 @@  static void free_nested(struct vcpu_vmx *vmx)
 
 /* Emulate the VMXOFF instruction */
 static int handle_vmoff(struct kvm_vcpu *vcpu)
 {
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 	free_nested(to_vmx(vcpu));
 	nested_vmx_succeed(vcpu);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 /* Emulate the VMCLEAR instruction */
 static int handle_vmclear(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	gpa_t vmptr;
 	struct vmcs12 *vmcs12;
@@ -7120,18 +7103,17 @@  static int handle_vmclear(struct kvm_vcpu *vcpu)
 	vmcs12 = kmap(page);
 	vmcs12->launch_state = 0;
 	kunmap(page);
 	nested_release_page(page);
 
 	nested_free_vmcs02(vmx, vmptr);
 
 	nested_vmx_succeed(vcpu);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch);
 
 /* Emulate the VMLAUNCH instruction */
 static int handle_vmlaunch(struct kvm_vcpu *vcpu)
 {
 	return nested_vmx_run(vcpu, true);
@@ -7335,28 +7317,25 @@  static int handle_vmread(struct kvm_vcpu *vcpu)
 	u64 field_value;
 	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 	u32 vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
 	gva_t gva = 0;
 
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (!nested_vmx_check_vmcs12(vcpu)) {
-		skip_emulated_instruction(vcpu);
-		return 1;
-	}
+	if (!nested_vmx_check_vmcs12(vcpu))
+		return kvm_skip_emulated_instruction(vcpu);
 
 	/* Decode instruction info and find the field to read */
 	field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
 	/* Read the field, zero-extended to a u64 field_value */
 	if (vmcs12_read_any(vcpu, field, &field_value) < 0) {
 		nested_vmx_failValid(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 	/*
 	 * Now copy part of this value to register or memory, as requested.
 	 * Note that the number of bits actually copied is 32 or 64 depending
 	 * on the guest's mode (32 or 64 bit), not on the given field's length.
 	 */
 	if (vmx_instruction_info & (1u << 10)) {
 		kvm_register_writel(vcpu, (((vmx_instruction_info) >> 3) & 0xf),
@@ -7366,18 +7345,17 @@  static int handle_vmread(struct kvm_vcpu *vcpu)
 				vmx_instruction_info, true, &gva))
 			return 1;
 		/* _system ok, as nested_vmx_check_permission verified cpl=0 */
 		kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, gva,
 			     &field_value, (is_long_mode(vcpu) ? 8 : 4), NULL);
 	}
 
 	nested_vmx_succeed(vcpu);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 
 static int handle_vmwrite(struct kvm_vcpu *vcpu)
 {
 	unsigned long field;
 	gva_t gva;
 	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
@@ -7389,20 +7367,18 @@  static int handle_vmwrite(struct kvm_vcpu *vcpu)
 	 * bits into the vmcs12 field.
 	 */
 	u64 field_value = 0;
 	struct x86_exception e;
 
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (!nested_vmx_check_vmcs12(vcpu)) {
-		skip_emulated_instruction(vcpu);
-		return 1;
-	}
+	if (!nested_vmx_check_vmcs12(vcpu))
+		return kvm_skip_emulated_instruction(vcpu);
 
 	if (vmx_instruction_info & (1u << 10))
 		field_value = kvm_register_readl(vcpu,
 			(((vmx_instruction_info) >> 3) & 0xf));
 	else {
 		if (get_vmx_mem_address(vcpu, exit_qualification,
 				vmx_instruction_info, false, &gva))
 			return 1;
@@ -7413,29 +7389,26 @@  static int handle_vmwrite(struct kvm_vcpu *vcpu)
 		}
 	}
 
 
 	field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
 	if (vmcs_field_readonly(field)) {
 		nested_vmx_failValid(vcpu,
 			VMXERR_VMWRITE_READ_ONLY_VMCS_COMPONENT);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	if (vmcs12_write_any(vcpu, field, field_value) < 0) {
 		nested_vmx_failValid(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	nested_vmx_succeed(vcpu);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 /* Emulate the VMPTRLD instruction */
 static int handle_vmptrld(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	gpa_t vmptr;
 
@@ -7446,27 +7419,25 @@  static int handle_vmptrld(struct kvm_vcpu *vcpu)
 		return 1;
 
 	if (vmx->nested.current_vmptr != vmptr) {
 		struct vmcs12 *new_vmcs12;
 		struct page *page;
 		page = nested_get_page(vcpu, vmptr);
 		if (page == NULL) {
 			nested_vmx_failInvalid(vcpu);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 		new_vmcs12 = kmap(page);
 		if (new_vmcs12->revision_id != VMCS12_REVISION) {
 			kunmap(page);
 			nested_release_page_clean(page);
 			nested_vmx_failValid(vcpu,
 				VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 
 		nested_release_vmcs12(vmx);
 		vmx->nested.current_vmptr = vmptr;
 		vmx->nested.current_vmcs12 = new_vmcs12;
 		vmx->nested.current_vmcs12_page = page;
 		/*
 		 * Load VMCS12 from guest memory since it is not already
@@ -7480,18 +7451,17 @@  static int handle_vmptrld(struct kvm_vcpu *vcpu)
 				      SECONDARY_EXEC_SHADOW_VMCS);
 			vmcs_write64(VMCS_LINK_POINTER,
 				     __pa(vmx->vmcs01.shadow_vmcs));
 			vmx->nested.sync_shadow_vmcs = true;
 		}
 	}
 
 	nested_vmx_succeed(vcpu);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 /* Emulate the VMPTRST instruction */
 static int handle_vmptrst(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 	u32 vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
 	gva_t vmcs_gva;
@@ -7506,18 +7476,17 @@  static int handle_vmptrst(struct kvm_vcpu *vcpu)
 	/* ok to use *_system, as nested_vmx_check_permission verified cpl=0 */
 	if (kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, vmcs_gva,
 				 (void *)&to_vmx(vcpu)->nested.current_vmptr,
 				 sizeof(u64), &e)) {
 		kvm_inject_page_fault(vcpu, &e);
 		return 1;
 	}
 	nested_vmx_succeed(vcpu);
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 /* Emulate the INVEPT instruction */
 static int handle_invept(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 vmx_instruction_info, types;
 	unsigned long type;
@@ -7545,18 +7514,17 @@  static int handle_invept(struct kvm_vcpu *vcpu)
 	vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
 	type = kvm_register_readl(vcpu, (vmx_instruction_info >> 28) & 0xf);
 
 	types = (vmx->nested.nested_vmx_ept_caps >> VMX_EPT_EXTENT_SHIFT) & 6;
 
 	if (type >= 32 || !(types & (1 << type))) {
 		nested_vmx_failValid(vcpu,
 				VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	/* According to the Intel VMX instruction reference, the memory
 	 * operand is read even if it isn't needed (e.g., for type==global)
 	 */
 	if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
 			vmx_instruction_info, false, &gva))
 		return 1;
@@ -7577,18 +7545,17 @@  static int handle_invept(struct kvm_vcpu *vcpu)
 		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
 		nested_vmx_succeed(vcpu);
 		break;
 	default:
 		BUG_ON(1);
 		break;
 	}
 
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_invvpid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 vmx_instruction_info;
 	unsigned long type, types;
 	gva_t gva;
@@ -7609,18 +7576,17 @@  static int handle_invvpid(struct kvm_vcpu *vcpu)
 	type = kvm_register_readl(vcpu, (vmx_instruction_info >> 28) & 0xf);
 
 	types = (vmx->nested.nested_vmx_vpid_caps &
 			VMX_VPID_EXTENT_SUPPORTED_MASK) >> 8;
 
 	if (type >= 32 || !(types & (1 << type))) {
 		nested_vmx_failValid(vcpu,
 			VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	/* according to the intel vmx instruction reference, the memory
 	 * operand is read even if it isn't needed (e.g., for type==global)
 	 */
 	if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
 			vmx_instruction_info, false, &gva))
 		return 1;
@@ -7632,33 +7598,30 @@  static int handle_invvpid(struct kvm_vcpu *vcpu)
 
 	switch (type) {
 	case VMX_VPID_EXTENT_INDIVIDUAL_ADDR:
 	case VMX_VPID_EXTENT_SINGLE_CONTEXT:
 	case VMX_VPID_EXTENT_SINGLE_NON_GLOBAL:
 		if (!vpid) {
 			nested_vmx_failValid(vcpu,
 				VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);
-			skip_emulated_instruction(vcpu);
-			return 1;
+			return kvm_skip_emulated_instruction(vcpu);
 		}
 		break;
 	case VMX_VPID_EXTENT_ALL_CONTEXT:
 		break;
 	default:
 		WARN_ON_ONCE(1);
-		skip_emulated_instruction(vcpu);
-		return 1;
+		return kvm_skip_emulated_instruction(vcpu);
 	}
 
 	__vmx_flush_tlb(vcpu, vmx->nested.vpid02);
 	nested_vmx_succeed(vcpu);
 
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 static int handle_pml_full(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification;
 
 	trace_kvm_pml_full(vcpu->vcpu_id);
 
@@ -10189,16 +10152,21 @@  static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 	 * We're finally done with prerequisite checking, and can start with
 	 * the nested entry.
 	 */
 
 	vmcs02 = nested_get_current_vmcs02(vmx);
 	if (!vmcs02)
 		return -ENOMEM;
 
+	/*
+	 * After this point, the trap flag no longer triggers a singlestep trap
+	 * on the vm entry instructions. Don't call
+	 * kvm_skip_emulated_instruction.
+	 */
 	skip_emulated_instruction(vcpu);
 	enter_guest_mode(vcpu);
 
 	if (!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS))
 		vmx->nested.vmcs01_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL);
 
 	cpu = get_cpu();
 	vmx->loaded_vmcs = vmcs02;
@@ -10233,18 +10201,17 @@  static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 	 * Note no nested_vmx_succeed or nested_vmx_fail here. At this point
 	 * we are no longer running L1, and VMLAUNCH/VMRESUME has not yet
 	 * returned as far as L1 is concerned. It will only return (and set
 	 * the success flag) when L2 exits (see nested_vmx_vmexit()).
 	 */
 	return 1;
 
 out:
-	skip_emulated_instruction(vcpu);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 /*
  * On a nested exit from L2 to L1, vmcs12.guest_cr0 might not be up-to-date
  * because L2 may have changed some cr0 bits directly (CRO_GUEST_HOST_MASK).
  * This function returns the new value we should put in vmcs12.guest_cr0.
  * It's not enough to just return the vmcs02 GUEST_CR0. Rather,
  *  1. Bits that neither L0 nor L1 trapped, were set directly by L2 and are now
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ec59301..7b38c5e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -420,22 +420,24 @@  void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
 EXPORT_SYMBOL_GPL(kvm_queue_exception);
 
 void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr)
 {
 	kvm_multiple_exception(vcpu, nr, false, 0, true);
 }
 EXPORT_SYMBOL_GPL(kvm_requeue_exception);
 
-void kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err)
+int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err)
 {
 	if (err)
 		kvm_inject_gp(vcpu, 0);
 	else
-		kvm_x86_ops->skip_emulated_instruction(vcpu);
+		return kvm_skip_emulated_instruction(vcpu);
+
+	return 1;
 }
 EXPORT_SYMBOL_GPL(kvm_complete_insn_gp);
 
 void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
 {
 	++vcpu->stat.pf_guest;
 	vcpu->arch.cr2 = fault->address;
 	kvm_queue_exception_e(vcpu, PF_VECTOR, fault->error_code);
@@ -4808,18 +4810,18 @@  static int kvm_emulate_wbinvd_noskip(struct kvm_vcpu *vcpu)
 		cpumask_clear(vcpu->arch.wbinvd_dirty_mask);
 	} else
 		wbinvd();
 	return X86EMUL_CONTINUE;
 }
 
 int kvm_emulate_wbinvd(struct kvm_vcpu *vcpu)
 {
-	kvm_x86_ops->skip_emulated_instruction(vcpu);
-	return kvm_emulate_wbinvd_noskip(vcpu);
+	kvm_emulate_wbinvd_noskip(vcpu);
+	return kvm_skip_emulated_instruction(vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_wbinvd);
 
 
 
 static void emulator_wbinvd(struct x86_emulate_ctxt *ctxt)
 {
 	kvm_emulate_wbinvd_noskip(emul_to_vcpu(ctxt));
@@ -5425,16 +5427,27 @@  static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, unsigned long rflag
 			 */
 			vcpu->arch.dr6 &= ~15;
 			vcpu->arch.dr6 |= DR6_BS | DR6_RTM;
 			kvm_queue_exception(vcpu, DB_VECTOR);
 		}
 	}
 }
 
+int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
+{
+	unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
+	int r = EMULATE_DONE;
+
+	kvm_x86_ops->skip_emulated_instruction(vcpu);
+	kvm_vcpu_check_singlestep(vcpu, rflags, &r);
+	return r == EMULATE_DONE;
+}
+EXPORT_SYMBOL_GPL(kvm_skip_emulated_instruction);
+
 static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
 {
 	if (unlikely(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) &&
 	    (vcpu->arch.guest_debug_dr7 & DR7_BP_EN_MASK)) {
 		struct kvm_run *kvm_run = vcpu->run;
 		unsigned long eip = kvm_get_linear_rip(vcpu);
 		u32 dr6 = kvm_vcpu_check_hw_bp(eip, 0,
 					   vcpu->arch.guest_debug_dr7,
@@ -6002,18 +6015,22 @@  int kvm_vcpu_halt(struct kvm_vcpu *vcpu)
 		vcpu->run->exit_reason = KVM_EXIT_HLT;
 		return 0;
 	}
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_halt);
 
 int kvm_emulate_halt(struct kvm_vcpu *vcpu)
 {
-	kvm_x86_ops->skip_emulated_instruction(vcpu);
-	return kvm_vcpu_halt(vcpu);
+	int ret = kvm_skip_emulated_instruction(vcpu);
+	/*
+	 * TODO: we might be squashing a GUESTDBG_SINGLESTEP-triggered
+	 * KVM_EXIT_DEBUG here.
+	 */
+	return kvm_vcpu_halt(vcpu) && ret;
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_halt);
 
 /*
  * kvm_pv_kick_cpu_op:  Kick a vcpu.
  *
  * @apicid - apicid of vcpu to be kicked.
  */
@@ -6034,19 +6051,19 @@  void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
 {
 	vcpu->arch.apicv_active = false;
 	kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
 }
 
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 {
 	unsigned long nr, a0, a1, a2, a3, ret;
-	int op_64_bit, r = 1;
+	int op_64_bit, r;
 
-	kvm_x86_ops->skip_emulated_instruction(vcpu);
+	r = kvm_skip_emulated_instruction(vcpu);
 
 	if (kvm_hv_hypercall_enabled(vcpu->kvm))
 		return kvm_hv_hypercall(vcpu);
 
 	nr = kvm_register_read(vcpu, VCPU_REGS_RAX);
 	a0 = kvm_register_read(vcpu, VCPU_REGS_RBX);
 	a1 = kvm_register_read(vcpu, VCPU_REGS_RCX);
 	a2 = kvm_register_read(vcpu, VCPU_REGS_RDX);