target-i386: tcg: Accept clwb instruction

Accept the clwb instruction (66 0F AE /6) if its corresponding feature
flag is enabled on CPUID[7].

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

target-i386/translate.c

@@ -7716,10 +7716,21 @@ static target_ulong disas_insn(CPUX86State *env, DisasContext *s,
             }
             break;
         case 5: /* lfence */
-        case 6: /* mfence */
             if ((modrm & 0xc7) != 0xc0 || !(s->cpuid_features & CPUID_SSE2))
                 goto illegal_op;
             break;
+        case 6: /* mfence/clwb */
+            if (s->prefix & PREFIX_DATA) {
+                /* clwb */
+                if (!(s->cpuid_7_0_ebx_features & CPUID_7_0_EBX_CLWB))
+                    goto illegal_op;
+                gen_nop_modrm(env, s, modrm);
+            } else {
+                /* mfence */
+                if ((modrm & 0xc7) != 0xc0 || !(s->cpuid_features & CPUID_SSE2))
+                    goto illegal_op;
+            }
+            break;
         case 7: /* sfence / clflush */
             if ((modrm & 0xc7) == 0xc0) {
                 /* sfence */