x86emul: check for FPU availability

We can't exclude someone wanting to hide the FPU from guests.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper@xxxxxxxxxx>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1246,6 +1246,7 @@ static bool_t vcpu_has(
 
 #define vcpu_must_have(leaf, reg, bit) \
     generate_exception_if(!vcpu_has(leaf, reg, bit, ctxt, ops), EXC_UD, -1)
+#define vcpu_must_have_fpu()  vcpu_must_have(0x00000001, EDX, 0)
 #define vcpu_must_have_mmx()  vcpu_must_have(0x00000001, EDX, 23)
 #define vcpu_must_have_sse()  vcpu_must_have(0x00000001, EDX, 25)
 #define vcpu_must_have_sse2() vcpu_must_have(0x00000001, EDX, 26)
@@ -3107,6 +3108,7 @@ x86_emulate(
     {
         struct fpu_insn_ctxt fic = { .insn_bytes = 1 };
 
+        host_and_vcpu_must_have(fpu);
         get_fpu(X86EMUL_FPU_wait, &fic);
         asm volatile ( "fwait" ::: "memory" );
         put_fpu(&fic);
@@ -3479,6 +3481,7 @@ x86_emulate(
     }
 
     case 0xd8: /* FPU 0xd8 */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xc0 ... 0xc7: /* fadd %stN,%stN */
@@ -3529,6 +3532,7 @@ x86_emulate(
         break;
 
     case 0xd9: /* FPU 0xd9 */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xfb: /* fsincos */
@@ -3612,6 +3616,7 @@ x86_emulate(
         break;
 
     case 0xda: /* FPU 0xda */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xc0 ... 0xc7: /* fcmovb %stN */
@@ -3659,6 +3664,7 @@ x86_emulate(
         break;
 
     case 0xdb: /* FPU 0xdb */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xc0 ... 0xc7: /* fcmovnb %stN */
@@ -3731,6 +3737,7 @@ x86_emulate(
         break;
 
     case 0xdc: /* FPU 0xdc */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xc0 ... 0xc7: /* fadd %stN */
@@ -3779,6 +3786,7 @@ x86_emulate(
         break;
 
     case 0xdd: /* FPU 0xdd */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xc0 ... 0xc7: /* ffree %stN */
@@ -3832,6 +3840,7 @@ x86_emulate(
         break;
 
     case 0xde: /* FPU 0xde */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xc0 ... 0xc7: /* faddp %stN */
@@ -3881,6 +3890,7 @@ x86_emulate(
         break;
 
     case 0xdf: /* FPU 0xdf */
+        host_and_vcpu_must_have(fpu);
         switch ( modrm )
         {
         case 0xe0: