x86emul: suppress reads for unhandled 0f38/0f3a extension space insns

The way these extension spaces get handled we so far always end up
going through the generic SrcMem operand fetch path for unused table
entries. Suppress actual memory accesses happening by forcing op_bytes
to zero in those cases.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
RFC: There are still some gaps left, but I think those are tolerable
     as they would only affect truly invalid instructions (for which
     delivering undefined behavior should be acceptable).

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -2343,7 +2343,11 @@ x86_decode_0f38(
     switch ( ctxt->opcode & X86EMUL_OPC_MASK )
     {
     case 0x00 ... 0xef:
-    case 0xf2 ... 0xff:
+    case 0xf2 ... 0xf5:
+    case 0xf7 ... 0xff:
+        op_bytes = 0;
+        /* fall through */
+    case 0xf6: /* adcx / adox */
         ctxt->opcode |= MASK_INSR(vex.pfx, X86EMUL_OPC_PFX_MASK);
         break;
 
@@ -2359,6 +2363,22 @@ x86_decode_0f38(
         if ( rep_prefix() )
             ctxt->opcode |= MASK_INSR(vex.pfx, X86EMUL_OPC_PFX_MASK);
         break;
+
+    case X86EMUL_OPC_VEX(0, 0xf2):    /* andn */
+    case X86EMUL_OPC_VEX(0, 0xf3):    /* Grp 17 */
+    case X86EMUL_OPC_VEX(0, 0xf5):    /* bzhi */
+    case X86EMUL_OPC_VEX_F3(0, 0xf5): /* pext */
+    case X86EMUL_OPC_VEX_F2(0, 0xf5): /* pdep */
+    case X86EMUL_OPC_VEX_F2(0, 0xf6): /* mulx */
+    case X86EMUL_OPC_VEX(0, 0xf7):    /* bextr */
+    case X86EMUL_OPC_VEX_66(0, 0xf7): /* shlx */
+    case X86EMUL_OPC_VEX_F3(0, 0xf7): /* sarx */
+    case X86EMUL_OPC_VEX_F2(0, 0xf7): /* shrx */
+        break;
+
+    default:
+        op_bytes = 0;
+        break;
     }
 
     return X86EMUL_OKAY;
@@ -2375,6 +2395,13 @@ x86_decode_0f3a(
 
     switch ( ctxt->opcode & X86EMUL_OPC_MASK )
     {
+    case X86EMUL_OPC_66(0, 0x14)
+     ... X86EMUL_OPC_66(0, 0x17):     /* pextr*, extractps */
+    case X86EMUL_OPC_VEX_66(0, 0x14)
+     ... X86EMUL_OPC_VEX_66(0, 0x17): /* vpextr*, vextractps */
+    case X86EMUL_OPC_VEX_F2(0, 0xf0): /* rorx */
+        break;
+
     case X86EMUL_OPC_66(0, 0x20):     /* pinsrb */
     case X86EMUL_OPC_VEX_66(0, 0x20): /* vpinsrb */
         state->desc = DstImplicit | SrcMem;
@@ -2386,6 +2413,10 @@ x86_decode_0f3a(
     case X86EMUL_OPC_VEX_66(0, 0x22): /* vpinsr{d,q} */
         state->desc = DstImplicit | SrcMem;
         break;
+
+    default:
+        op_bytes = 0;
+        break;
     }
 
     return X86EMUL_OKAY;