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

@@ -7317,35 +7317,21 @@ static bool is_vmware_backdoor_opcode(struct x86_emulate_ctxt *ctxt)
 	return false;
 }
 
-int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
-			    int emulation_type, void *insn, int insn_len)
+/*
+ * 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;
+	int r = EMULATION_OK;
 	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
-	bool writeback = true;
-	bool write_fault_to_spt;
-
-	if (unlikely(!kvm_x86_ops.can_emulate_instruction(vcpu, insn, insn_len)))
-		return 1;
-
-	vcpu->arch.l1tf_flush_l1d = true;
 
-	/*
-	 * Clear write_fault_to_shadow_pgtable here to ensure it is
-	 * never reused.
-	 */
-	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.
+	 * 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))
@@ -7362,6 +7348,36 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 
 	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)
+{
+	int r;
+	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+	bool writeback = true;
+	bool write_fault_to_spt;
+
+	if (unlikely(!kvm_x86_ops.can_emulate_instruction(vcpu, insn, insn_len)))
+		return 1;
+
+	vcpu->arch.l1tf_flush_l1d = true;
+
+	/*
+	 * Clear write_fault_to_shadow_pgtable here to ensure it is
+	 * never reused.
+	 */
+	write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
+	vcpu->arch.write_fault_to_shadow_pgtable = false;
+
+	if (!(emulation_type & EMULTYPE_NO_DECODE)) {
+		kvm_clear_exception_queue(vcpu);
+
+		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);