[xen master] x86: introduce x86_seg_sys

[patchbot@xxxxxxx]

commit 34d4227e6a018aa19cc2996564ea6bd34f18ae9a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Sep 30 10:05:25 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 30 10:05:25 2024 +0200

    x86: introduce x86_seg_sys
    
    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).
    
    While there also add x86_seg_none handling to the test harness'es
    read() hook, as will be needed for MSR-LIST support.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/tests/x86_emulator/test_x86_emulator.c | 2 ++
 xen/arch/x86/hvm/emulate.c                   | 2 +-
 xen/arch/x86/hvm/hvm.c                       | 2 +-
 xen/arch/x86/hvm/svm/svm.c                   | 1 +
 xen/arch/x86/x86_emulate/x86_emulate.h       | 3 ++-
 5 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/tools/tests/x86_emulator/test_x86_emulator.c 
b/tools/tests/x86_emulator/test_x86_emulator.c
index 24343c5d7f..d52c1c53cb 100644
--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -593,6 +593,8 @@ 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;
     }
diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index ecf83795fa..aa97ca1cbf 100644
--- 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;
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index a64eead368..b2e782d596 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2599,7 +2599,7 @@ 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);
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 92bb10c504..e0793b26db 100644
--- 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_register(
         vmcb->ldtr = *reg;
         break;
 
+    case x86_seg_sys:
     case x86_seg_none:
         ASSERT_UNREACHABLE();
         break;
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h 
b/xen/arch/x86/x86_emulate/x86_emulate.h
index e8a0e57228..3e819d4174 100644
--- 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
 };
 
--
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