x86/emul: Fix the emulation of invlpga

The instruction requires EFER.SVME set to be usable in the first place.

Furthermore, the emulation doesn't handle ASIDs, so avoid giving the
impression that they work.  Permit ASID 0 which is reserved for non-root
mode (in which case the instruction is identical to invlpg), but raise #UD for
any other ASID.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -5120,8 +5120,15 @@ x86_emulate(
             break;
 
         case 0xdf: /* invlpga */
-            generate_exception_if(!in_protmode(ctxt, ops), EXC_UD);
+            fail_if(!ops->read_msr);
+            if ( (rc = ops->read_msr(MSR_EFER,
+                                     &msr_val, ctxt)) != X86EMUL_OKAY )
+                goto done;
+            /* Finding SVME set implies vcpu_has_svm(). */
+            generate_exception_if(!(msr_val & EFER_SVME) ||
+                                  !in_protmode(ctxt, ops), EXC_UD);
             generate_exception_if(!mode_ring0(), EXC_GP, 0);
+            generate_exception_if(_regs.ecx, EXC_UD); /* TODO: Support ASIDs. */
             fail_if(ops->invlpg == NULL);
             if ( (rc = ops->invlpg(x86_seg_none, truncate_ea(_regs.r(ax)),
                                    ctxt)) )