diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index d3006f094a69..76467b76c047 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -2433,14 +2433,15 @@ static void cf_check hvmemul_put_fpu(
 
         switch ( mode )
         {
-        case 8:
+        case X86_MODE_64BIT:
             fpu_ctxt->fip.addr = aux->ip;
             if ( dval )
                 fpu_ctxt->fdp.addr = aux->dp;
             fpu_ctxt->x[FPU_WORD_SIZE_OFFSET] = 8;
             break;
 
-        case 4: case 2:
+        case X86_MODE_32BIT:
+        case X86_MODE_16BIT:
             fpu_ctxt->fip.offs = aux->ip;
             fpu_ctxt->fip.sel  = aux->cs;
             if ( dval )
@@ -2451,7 +2452,8 @@ static void cf_check hvmemul_put_fpu(
             fpu_ctxt->x[FPU_WORD_SIZE_OFFSET] = mode;
             break;
 
-        case 0: case 1:
+        case X86_MODE_REAL:
+        case X86_MODE_VM86:
             fpu_ctxt->fip.addr = aux->ip | (aux->cs << 4);
             if ( dval )
                 fpu_ctxt->fdp.addr = aux->dp | (aux->ds << 4);
@@ -2952,11 +2954,11 @@ static const char *guest_x86_mode_to_str(int mode)
 {
     switch ( mode )
     {
-    case 0:  return "Real";
-    case 1:  return "v86";
-    case 2:  return "16bit";
-    case 4:  return "32bit";
-    case 8:  return "64bit";
+    case X86_MODE_REAL:   return "Real";
+    case X86_MODE_VM86:   return "v86";
+    case X86_MODE_16BIT:  return "16bit";
+    case X86_MODE_32BIT:  return "32bit";
+    case X86_MODE_64BIT:  return "64bit";
     default: return "Unknown";
     }
 }
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 74e58c653e6f..922c9b3af64d 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3974,7 +3974,9 @@ static void hvm_latch_shinfo_size(struct domain *d)
      */
     if ( current->domain == d )
     {
-        d->arch.has_32bit_shinfo = (hvm_guest_x86_mode(current) != 8);
+        d->arch.has_32bit_shinfo =
+            hvm_guest_x86_mode(current) != X86_MODE_64BIT;
+
         /*
          * Make sure that the timebase in the shared info structure is correct.
          *
diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
index 81883c8d4f60..6f8dfdff4ac6 100644
--- a/xen/arch/x86/hvm/hypercall.c
+++ b/xen/arch/x86/hvm/hypercall.c
@@ -112,23 +112,24 @@ int hvm_hypercall(struct cpu_user_regs *regs)
 
     switch ( mode )
     {
-    case 8:
+    case X86_MODE_64BIT:
         eax = regs->rax;
         fallthrough;
-    case 4:
-    case 2:
+    case X86_MODE_32BIT:
+    case X86_MODE_16BIT:
         if ( currd->arch.monitor.guest_request_userspace_enabled &&
-            eax == __HYPERVISOR_hvm_op &&
-            (mode == 8 ? regs->rdi : regs->ebx) == HVMOP_guest_request_vm_event )
+             eax == __HYPERVISOR_hvm_op &&
+             (mode == X86_MODE_64BIT ? regs->rdi : regs->ebx) ==
+             HVMOP_guest_request_vm_event )
             break;
 
         if ( likely(!hvm_get_cpl(curr)) )
             break;
         fallthrough;
-    default:
+    case X86_MODE_VM86:
         regs->rax = -EPERM;
         return HVM_HCALL_completed;
-    case 0:
+    case X86_MODE_REAL:
         break;
     }
 
@@ -198,7 +199,7 @@ enum mc_disposition hvm_do_multicall_call(struct mc_state *state)
 {
     struct vcpu *curr = current;
 
-    if ( hvm_guest_x86_mode(curr) == 8 )
+    if ( hvm_guest_x86_mode(curr) == X86_MODE_64BIT )
     {
         struct multicall_entry *call = &state->call;
 
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index b8f87aa1ed08..62905c2c7acd 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -571,12 +571,12 @@ static int cf_check svm_guest_x86_mode(struct vcpu *v)
     struct vmcb_struct *vmcb = v->arch.hvm.svm.vmcb;
 
     if ( unlikely(!(v->arch.hvm.guest_cr[0] & X86_CR0_PE)) )
-        return 0;
+        return X86_MODE_REAL;
     if ( unlikely(guest_cpu_user_regs()->eflags & X86_EFLAGS_VM) )
-        return 1;
+        return X86_MODE_VM86;
     if ( hvm_long_mode_active(v) && likely(vmcb->cs.l) )
-        return 8;
-    return likely(vmcb->cs.db) ? 4 : 2;
+        return X86_MODE_64BIT;
+    return vmcb->cs.db ? X86_MODE_32BIT : X86_MODE_16BIT;
 }
 
 static void cf_check svm_cpuid_policy_changed(struct vcpu *v)
diff --git a/xen/arch/x86/hvm/viridian/viridian.c b/xen/arch/x86/hvm/viridian/viridian.c
index 21480d9ee700..33d54e587edf 100644
--- a/xen/arch/x86/hvm/viridian/viridian.c
+++ b/xen/arch/x86/hvm/viridian/viridian.c
@@ -933,13 +933,13 @@ int viridian_hypercall(struct cpu_user_regs *regs)
 
     switch ( mode )
     {
-    case 8:
+    case X86_MODE_64BIT:
         input.raw = regs->rcx;
         input_params_gpa = regs->rdx;
         output_params_gpa = regs->r8;
         break;
 
-    case 4:
+    case X86_MODE_32BIT:
         input.raw = (regs->rdx << 32) | regs->eax;
         input_params_gpa = (regs->rbx << 32) | regs->ecx;
         output_params_gpa = (regs->rdi << 32) | regs->esi;
@@ -1038,11 +1038,11 @@ int viridian_hypercall(struct cpu_user_regs *regs)
 
     switch ( mode )
     {
-    case 8:
+    case X86_MODE_64BIT:
         regs->rax = output.raw;
         break;
 
-    case 4:
+    case X86_MODE_32BIT:
         regs->rdx = output.raw >> 32;
         regs->rax = (uint32_t)output.raw;
         break;
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index b6885d0e2764..eee1d4b47a13 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -886,14 +886,15 @@ int cf_check vmx_guest_x86_mode(struct vcpu *v)
     unsigned long cs_ar_bytes;
 
     if ( unlikely(!(v->arch.hvm.guest_cr[0] & X86_CR0_PE)) )
-        return 0;
+        return X86_MODE_REAL;
     if ( unlikely(guest_cpu_user_regs()->eflags & X86_EFLAGS_VM) )
-        return 1;
+        return X86_MODE_VM86;
     __vmread(GUEST_CS_AR_BYTES, &cs_ar_bytes);
     if ( hvm_long_mode_active(v) &&
          likely(cs_ar_bytes & X86_SEG_AR_CS_LM_ACTIVE) )
-        return 8;
-    return (likely(cs_ar_bytes & X86_SEG_AR_DEF_OP_SIZE) ? 4 : 2);
+        return X86_MODE_64BIT;
+    return (likely(cs_ar_bytes & X86_SEG_AR_DEF_OP_SIZE)
+            ? X86_MODE_32BIT : X86_MODE_16BIT);
 }
 
 static void vmx_save_dr(struct vcpu *v)
diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
index 78135ca23be8..cf47d61b1473 100644
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -411,7 +411,7 @@ static int decode_vmx_inst(struct cpu_user_regs *regs,
     }
     else
     {
-        bool mode_64bit = (vmx_guest_x86_mode(v) == 8);
+        bool mode_64bit = vmx_guest_x86_mode(v) == X86_MODE_64BIT;
 
         decode->type = VMX_INST_MEMREG_TYPE_MEMORY;
 
@@ -2073,7 +2073,8 @@ int nvmx_handle_vmx_insn(struct cpu_user_regs *regs, unsigned int exit_reason)
 
     if ( !(curr->arch.hvm.guest_cr[4] & X86_CR4_VMXE) ||
          !nestedhvm_enabled(curr->domain) ||
-         (vmx_guest_x86_mode(curr) < (hvm_long_mode_active(curr) ? 8 : 2)) ||
+         (vmx_guest_x86_mode(curr) <
+          (hvm_long_mode_active(curr) ? X86_MODE_64BIT : X86_MODE_16BIT)) ||
          (exit_reason != EXIT_REASON_VMXON && !nvmx_vcpu_in_vmx(curr)) )
     {
         hvm_inject_hw_exception(X86_EXC_UD, X86_EVENT_NO_EC);
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h b/xen/arch/x86/include/asm/hvm/hvm.h
index 02de18c7d4a8..124906a548da 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -26,6 +26,20 @@ extern bool opt_hvm_fep;
 #define opt_hvm_fep 0
 #endif
 
+/*
+ * Results for hvm_guest_x86_mode().
+ *
+ * Note, some callers depend on the order of these constants.
+ *
+ * TODO: Rework this helper to avoid implying mixing the architectural
+ * concepts of mode and operand size.
+ */
+#define X86_MODE_REAL  0
+#define X86_MODE_VM86  1
+#define X86_MODE_16BIT 2
+#define X86_MODE_32BIT 4
+#define X86_MODE_64BIT 8
+
 /* Interrupt acknowledgement sources. */
 enum hvm_intsrc {
     hvm_intsrc_none,
diff --git a/xen/arch/x86/oprofile/xenoprof.c b/xen/arch/x86/oprofile/xenoprof.c
index 247a0deca822..7f2525bfb4d6 100644
--- a/xen/arch/x86/oprofile/xenoprof.c
+++ b/xen/arch/x86/oprofile/xenoprof.c
@@ -86,11 +86,11 @@ int xenoprofile_get_mode(struct vcpu *curr, const struct cpu_user_regs *regs)
 
     switch ( hvm_guest_x86_mode(curr) )
     {
-    case 0: /* real mode */
+    case X86_MODE_REAL:
         return 1;
-    case 1: /* vm86 mode */
+    case X86_MODE_VM86:
         return 0;
-    default:
+    default: /* 16BIT | 32BIT | 64BIT */
         return hvm_get_cpl(curr) != 3;
     }
 }
