KVM: x86: Add kvm_skip_emulated_instruction and use it.

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 <khuey@kylehuey.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

1 files changed, 25 insertions, 8 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ec59301f5192..7b38c5e6f412 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -425,12 +425,14 @@ void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr)
 }
 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);
 
@@ -4813,8 +4815,8 @@ static int kvm_emulate_wbinvd_noskip(struct kvm_vcpu *vcpu)
 
 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);
 
@@ -5430,6 +5432,17 @@ static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, unsigned long rflag
 	}
 }
 
+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) &&
@@ -6007,8 +6020,12 @@ 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);
 
@@ -6039,9 +6056,9 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *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);