[PATCH v5 4/7] x86: introduce x86_seg_sys

[Jan Beulich <jbeulich@xxxxxxxx>]

To represent the USER-MSR bitmap access, a new segment type needs
introducing, behaving like x86_seg_none in terms of address treatment,
but behaving like a system segment for page walk purposes (implicit
supervisor-mode access).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
This feels a little fragile: Of course I did look through uses of the
enumerators, and I didn't find further places which would need
adjustment, but I'm not really sure I didn't miss any place.
---
v3: New.

--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -593,6 +593,7 @@ static int read(
     default:
         if ( !is_x86_user_segment(seg) )
             return X86EMUL_UNHANDLEABLE;
+    case x86_seg_sys:
     case x86_seg_none:
         bytes_read += bytes;
         break;
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -840,7 +840,7 @@ static int hvmemul_virtual_to_linear(
     int okay;
     unsigned long reps = 1;
 
-    if ( seg == x86_seg_none )
+    if ( seg == x86_seg_none || seg == x86_seg_sys )
     {
         *linear = offset;
         return X86EMUL_OKAY;
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2601,7 +2601,7 @@ bool hvm_vcpu_virtual_to_linear(
      * It is expected that the access rights of reg are suitable for seg (and
      * that this is enforced at the point that seg is loaded).
      */
-    ASSERT(seg < x86_seg_none);
+    ASSERT(seg < x86_seg_sys);
 
     /* However, check that insn fetches only ever specify CS. */
     ASSERT(access_type != hvm_access_insn_fetch || seg == x86_seg_cs);
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -749,6 +749,7 @@ static void cf_check svm_set_segment_reg
         vmcb->ldtr = *reg;
         break;
 
+    case x86_seg_sys:
     case x86_seg_none:
         ASSERT_UNREACHABLE();
         break;
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -43,7 +43,8 @@ enum x86_segment {
     x86_seg_ldtr,
     x86_seg_gdtr,
     x86_seg_idtr,
-    /* No Segment: For accesses which are already linear. */
+    /* No Segment: For (system/normal) accesses which are already linear. */
+    x86_seg_sys,
     x86_seg_none
 };