KVM: x86 emulator: allow storing emulator execution function in decode tables

Instead of looking up the opcode twice (once for decode flags, once for
the big execution switch) look up both flags and function in the decode tables.
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -190,6 +190,7 @@ struct decode_cache {
 	bool has_seg_override;
 	u8 seg_override;
 	unsigned int d;
+	int (*execute)(struct x86_emulate_ctxt *ctxt);
 	unsigned long regs[NR_VCPU_REGS];
 	unsigned long eip;
 	/* modrm */

arch/x86/kvm/emulate.c

@@ -106,6 +106,7 @@
 struct opcode {
 	u32 flags;
 	union {
+		int (*execute)(struct x86_emulate_ctxt *ctxt);
 		struct opcode *group;
 		struct group_dual *gdual;
 	} u;
@@ -120,6 +121,7 @@ struct group_dual {
 #define N    D(0)
 #define G(_f, _g) { .flags = ((_f) | Group), .u.group = (_g) }
 #define GD(_f, _g) { .flags = ((_f) | Group | GroupDual), .u.gdual = (_g) }
+#define I(_f, _e) { .flags = (_f), .u.execute = (_e) }
 
 static struct opcode group1[] = {
 	X7(D(Lock)), N
@@ -349,6 +351,7 @@ static struct opcode twobyte_table[256] = {
 #undef N
 #undef G
 #undef GD
+#undef I
 
 /* EFLAGS bit definitions. */
 #define EFLG_ID (1<<21)
@@ -1070,6 +1073,8 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
 		c->d |= opcode.flags;
 	}
 
+	c->execute = opcode.u.execute;
+
 	/* Unrecognised? */
 	if (c->d == 0 || (c->d & Undefined)) {
 		DPRINTF("Cannot emulate %02x\n", c->b);
@@ -2705,6 +2710,13 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
 
 special_insn:
 
+	if (c->execute) {
+		rc = c->execute(ctxt);
+		if (rc != X86EMUL_CONTINUE)
+			goto done;
+		goto writeback;
+	}
+
 	if (c->twobyte)
 		goto twobyte_insn;