x86emul: add memory operand low bits checks for ENQCMD{,S}

Already ISE rev 044 added text to this effect; rev 045 further dropped
leftover earlier text indicating the contrary:
- ENQCMD requires the low 32 bits of the memory operand to be clear,
- ENDCMDS requires bits 20...30 of the memory operand to be clear.

Fixes: d273859687 ("x86emul: support ENQCMD insns")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -10499,6 +10499,7 @@ x86_emulate(
             goto done;
         if ( vex.pfx == vex_f2 ) /* enqcmd */
         {
+            generate_exception_if(mmvalp->data32[0], EXC_GP, 0);
             fail_if(!ops->read_msr);
             if ( (rc = ops->read_msr(MSR_PASID, &msr_val,
                                      ctxt)) != X86EMUL_OKAY )
@@ -10506,7 +10507,8 @@ x86_emulate(
             generate_exception_if(!(msr_val & PASID_VALID), EXC_GP, 0);
             mmvalp->data32[0] = MASK_EXTR(msr_val, PASID_PASID_MASK);
         }
-        mmvalp->data32[0] &= ~0x7ff00000;
+        else
+            generate_exception_if(mmvalp->data32[0] & 0x7ff00000, EXC_GP, 0);
         state->blk = blk_enqcmd;
         if ( (rc = ops->blk(x86_seg_es, src.val, mmvalp, 64, &_regs.eflags,
                             state, ctxt)) != X86EMUL_OKAY )