x86emul: add EVEX decoding

This way we can at least size (and e.g. skip) them if needed, and we
also won't raise the wrong fault due to not having read all relevant
bytes.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
TBD: I'm kind of undecided whether to right away propagate evex.R into
     modrm_reg (and then also deal with the new meaning of evex.x for
     modrm_rm). Since that doesn't affect GPRs (and the extra bits
     would need masking off when accessing GPRs) I've left this out for
     now.

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -336,6 +336,27 @@ union vex {
         ptr[1] = rex | REX_PREFIX; \
 } while (0)
 
+union evex {
+    uint8_t raw[3];
+    struct {
+        uint8_t opcx:2;
+        uint8_t :2;
+        uint8_t R:1;
+        uint8_t b:1;
+        uint8_t x:1;
+        uint8_t r:1;
+        uint8_t pfx:2;
+        uint8_t evex:1;
+        uint8_t reg:4;
+        uint8_t w:1;
+        uint8_t opmsk:3;
+        uint8_t RX:1;
+        uint8_t bcst:1;
+        uint8_t lr:2;
+        uint8_t z:1;
+    };
+};
+
 #define rep_prefix()   (vex.pfx >= vex_f3)
 #define repe_prefix()  (vex.pfx == vex_f3)
 #define repne_prefix() (vex.pfx == vex_f2)
@@ -1596,6 +1617,7 @@ struct x86_emulate_state {
     bool lock_prefix;
     opcode_desc_t desc;
     union vex vex;
+    union evex evex;
     int override_seg;
 
     /*
@@ -1623,6 +1645,7 @@ struct x86_emulate_state {
 #define rex_prefix (state->rex_prefix)
 #define lock_prefix (state->lock_prefix)
 #define vex (state->vex)
+#define evex (state->evex)
 #define override_seg (state->override_seg)
 #define ea (state->ea)
 
@@ -1811,7 +1834,8 @@ x86_decode(
         modrm = insn_fetch_type(uint8_t);
         modrm_mod = (modrm & 0xc0) >> 6;
 
-        if ( !ext && ((b & ~1) == 0xc4 || (b == 0x8f && (modrm & 0x18))) )
+        if ( !ext && ((b & ~1) == 0xc4 || (b == 0x8f && (modrm & 0x18)) ||
+                      b == 0x62) )
             switch ( def_ad_bytes )
             {
             default:
@@ -1825,7 +1849,7 @@ x86_decode(
                     break;
                 /* fall through */
             case 8:
-                /* VEX / XOP */
+                /* VEX / XOP / EVEX */
                 generate_exception_if(rex_prefix || vex.pfx, EXC_UD, -1);
 
                 vex.raw[0] = modrm;
@@ -1852,6 +1876,14 @@ x86_decode(
                             op_bytes = 8;
                         }
                     }
+                    if ( b == 0x62 )
+                    {
+                        evex.raw[0] = vex.raw[0];
+                        evex.raw[1] = vex.raw[1];
+                        evex.raw[2] = insn_fetch_type(uint8_t);
+
+                        vex.opcx = evex.opcx;
+                    }
                 }
                 if ( mode_64bit() && !vex.r )
                     rex_prefix |= REX_R;