KVM: x86 emulator: convert DIV/IDIV to fastop

Since DIV and IDIV can generate exceptions, we need an additional output
parameter indicating whether an execption has occured.  To avoid increasing
register pressure on i386, we use %rsi, which is already allocated for
the fastop code pointer.

Gleb: added comment about fop usage as exception indication.
Signed-off-by: Avi Kivity <avi.kivity@gmail.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

arch/x86/kvm/emulate.c

@@ -183,6 +183,7 @@
  * src:    rdx        (in/out)
  * src2:   rcx        (in)
  * flags:  rflags     (in/out)
+ * ex:     rsi        (in:fastop pointer, out:zero if exception)
  *
  * Moreover, they are all exactly FASTOP_SIZE bytes long, so functions for
  * different operand sizes can be reached by calculation, rather than a jump
@@ -470,7 +471,10 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *));
 #define FOPNOP() FOP_ALIGN FOP_RET
 
 #define FOP1E(op,  dst) \
-	FOP_ALIGN #op " %" #dst " \n\t" FOP_RET
+	FOP_ALIGN "10: " #op " %" #dst " \n\t" FOP_RET
+
+#define FOP1EEX(op,  dst) \
+	FOP1E(op, dst) _ASM_EXTABLE(10b, kvm_fastop_exception)
 
 #define FASTOP1(op) \
 	FOP_START(op) \
@@ -489,6 +493,15 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *));
 	ON64(FOP1E(op, rcx)) \
 	FOP_END
 
+/* 1-operand, using src2 (for MUL/DIV r/m), with exceptions */
+#define FASTOP1SRC2EX(op, name) \
+	FOP_START(name) \
+	FOP1EEX(op, cl) \
+	FOP1EEX(op, cx) \
+	FOP1EEX(op, ecx) \
+	ON64(FOP1EEX(op, rcx)) \
+	FOP_END
+
 #define FOP2E(op,  dst, src)	   \
 	FOP_ALIGN #op " %" #src ", %" #dst " \n\t" FOP_RET
 
@@ -533,6 +546,9 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *));
 /* Special case for SETcc - 1 instruction per cc */
 #define FOP_SETCC(op) ".align 4; " #op " %al; ret \n\t"
 
+asm(".global kvm_fastop_exception \n"
+    "kvm_fastop_exception: xor %esi, %esi; ret");
+
 FOP_START(setcc)
 FOP_SETCC(seto)
 FOP_SETCC(setno)
@@ -1007,6 +1023,8 @@ FASTOP2(test);
 
 FASTOP1SRC2(mul, mul_ex);
 FASTOP1SRC2(imul, imul_ex);
+FASTOP1SRC2EX(div, div_ex);
+FASTOP1SRC2EX(idiv, idiv_ex);
 
 FASTOP3WCL(shld);
 FASTOP3WCL(shrd);
@@ -2131,26 +2149,6 @@ static int em_jmp_far(struct x86_emulate_ctxt *ctxt)
 	return X86EMUL_CONTINUE;
 }
 
-static int em_div_ex(struct x86_emulate_ctxt *ctxt)
-{
-	u8 de = 0;
-
-	emulate_1op_rax_rdx(ctxt, "div", de);
-	if (de)
-		return emulate_de(ctxt);
-	return X86EMUL_CONTINUE;
-}
-
-static int em_idiv_ex(struct x86_emulate_ctxt *ctxt)
-{
-	u8 de = 0;
-
-	emulate_1op_rax_rdx(ctxt, "idiv", de);
-	if (de)
-		return emulate_de(ctxt);
-	return X86EMUL_CONTINUE;
-}
-
 static int em_grp45(struct x86_emulate_ctxt *ctxt)
 {
 	int rc = X86EMUL_CONTINUE;
@@ -3734,8 +3732,8 @@ static const struct opcode group3[] = {
 	F(DstMem | SrcNone | Lock, em_neg),
 	F(DstXacc | Src2Mem, em_mul_ex),
 	F(DstXacc | Src2Mem, em_imul_ex),
-	I(DstXacc | Src2Mem, em_div_ex),
-	I(DstXacc | Src2Mem, em_idiv_ex),
+	F(DstXacc | Src2Mem, em_div_ex),
+	F(DstXacc | Src2Mem, em_idiv_ex),
 };
 
 static const struct opcode group4[] = {
@@ -4571,9 +4569,12 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *))
 	if (!(ctxt->d & ByteOp))
 		fop += __ffs(ctxt->dst.bytes) * FASTOP_SIZE;
 	asm("push %[flags]; popf; call *%[fastop]; pushf; pop %[flags]\n"
-	    : "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags)
-	: "c"(ctxt->src2.val), [fastop]"S"(fop));
+	    : "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags),
+	      [fastop]"+S"(fop)
+	    : "c"(ctxt->src2.val));
 	ctxt->eflags = (ctxt->eflags & ~EFLAGS_MASK) | (flags & EFLAGS_MASK);
+	if (!fop) /* exception is returned in fop variable */
+		return emulate_de(ctxt);
 	return X86EMUL_CONTINUE;
 }