KVM: x86: Factor out x86 instruction emulation with decoding

Move the instruction decode part out of x86_emulate_instruction() for it
to be used in other places. Also kvm_clear_exception_queue() is moved
inside the if-statement as it doesn't apply when KVM are coming back from
userspace.
Co-developed-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Message-Id: <20210126081831.570253-2-wei.huang2@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -7317,6 +7317,42 @@ static bool is_vmware_backdoor_opcode(struct x86_emulate_ctxt *ctxt)
 	return false;
 }
 
+/*
+ * Decode to be emulated instruction. Return EMULATION_OK if success.
+ */
+int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type,
+				    void *insn, int insn_len)
+{
+	int r = EMULATION_OK;
+	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+
+	init_emulate_ctxt(vcpu);
+
+	/*
+	 * We will reenter on the same instruction since we do not set
+	 * complete_userspace_io. This does not handle watchpoints yet,
+	 * those would be handled in the emulate_ops.
+	 */
+	if (!(emulation_type & EMULTYPE_SKIP) &&
+	    kvm_vcpu_check_breakpoint(vcpu, &r))
+		return r;
+
+	ctxt->interruptibility = 0;
+	ctxt->have_exception = false;
+	ctxt->exception.vector = -1;
+	ctxt->perm_ok = false;
+
+	ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
+
+	r = x86_decode_insn(ctxt, insn, insn_len);
+
+	trace_kvm_emulate_insn_start(vcpu);
+	++vcpu->stat.insn_emulation;
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(x86_decode_emulated_instruction);
+
 int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len)
 {
@@ -7336,32 +7372,12 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	 */
 	write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
 	vcpu->arch.write_fault_to_shadow_pgtable = false;
-	kvm_clear_exception_queue(vcpu);
 
 	if (!(emulation_type & EMULTYPE_NO_DECODE)) {
-		init_emulate_ctxt(vcpu);
-
-		/*
-		 * We will reenter on the same instruction since
-		 * we do not set complete_userspace_io.  This does not
-		 * handle watchpoints yet, those would be handled in
-		 * the emulate_ops.
-		 */
-		if (!(emulation_type & EMULTYPE_SKIP) &&
-		    kvm_vcpu_check_breakpoint(vcpu, &r))
-			return r;
-
-		ctxt->interruptibility = 0;
-		ctxt->have_exception = false;
-		ctxt->exception.vector = -1;
-		ctxt->perm_ok = false;
-
-		ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
-
-		r = x86_decode_insn(ctxt, insn, insn_len);
+		kvm_clear_exception_queue(vcpu);
 
-		trace_kvm_emulate_insn_start(vcpu);
-		++vcpu->stat.insn_emulation;
+		r = x86_decode_emulated_instruction(vcpu, emulation_type,
+						    insn, insn_len);
 		if (r != EMULATION_OK)  {
 			if ((emulation_type & EMULTYPE_TRAP_UD) ||
 			    (emulation_type & EMULTYPE_TRAP_UD_FORCED)) {

arch/x86/kvm/x86.h

@@ -273,6 +273,8 @@ bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
 					  int page_num);
 bool kvm_vector_hashing_enabled(void);
 void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_code);
+int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type,
+				    void *insn, int insn_len);
 int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len);
 fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);