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>

arch/x86/kvm/svm.c

@@ -3151,8 +3151,7 @@ static int skinit_interception(struct vcpu_svm *svm)
 
 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)
@@ -3275,9 +3274,7 @@ static int rdpmc_interception(struct vcpu_svm *svm)
 		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,
@@ -3374,9 +3371,7 @@ static int cr_interception(struct vcpu_svm *svm)
 		}
 		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)