[PATCH RFC 1/9] x86/traps: Names for system descriptor types

[Andrew Cooper <andrew.cooper3@citrix.com>]

Avoids some particularly obscure magic numbers

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Keir Fraser <keir@xen.org>
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/arch/x86/crash.c        |    2 +-
 xen/arch/x86/traps.c        |    8 ++++----
 xen/arch/x86/x86_64/traps.c |    4 ++--
 xen/include/asm-x86/desc.h  |    8 ++++++++
 xen/include/asm-x86/ldt.h   |    2 +-
 5 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index aed3b3e..97adf02 100644
--- a/xen/arch/x86/crash.c
+++ b/xen/arch/x86/crash.c
@@ -149,7 +149,7 @@ static void nmi_shootdown_cpus(void)
              * This update is safe from a security point of view, as this pcpu 
              * is never going to try to sysret back to a PV vcpu.
              */
-            _set_gate_lower(&idt_tables[i][TRAP_nmi], 14, 0, &trap_nop);
+            _set_gate_lower(&idt_tables[i][TRAP_nmi], DESC_TYPE_irq_gate, 0, &trap_nop);
             set_ist(&idt_tables[i][TRAP_machine_check], IST_NONE);
         }
         else
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 40366f1..1de70af 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -3431,8 +3431,8 @@ static void __set_intr_gate(unsigned int n, uint32_t dpl, void *addr)
     /* Keep secondary tables in sync with IRQ updates. */
     for ( i = 1; i < nr_cpu_ids; i++ )
         if ( idt_tables[i] != NULL )
-            _set_gate(&idt_tables[i][n], 14, dpl, addr);
-    _set_gate(&idt_table[n], 14, dpl, addr);
+            _set_gate(&idt_tables[i][n], DESC_TYPE_irq_gate, dpl, addr);
+    _set_gate(&idt_table[n], DESC_TYPE_irq_gate, dpl, addr);
 }
 
 static void set_swint_gate(unsigned int n, void *addr)
@@ -3457,12 +3457,12 @@ void load_TR(void)
         this_cpu(gdt_table) + TSS_ENTRY - FIRST_RESERVED_GDT_ENTRY,
         (unsigned long)tss,
         offsetof(struct tss_struct, __cacheline_filler) - 1,
-        9);
+        DESC_TYPE_tss_avail);
     _set_tssldt_desc(
         this_cpu(compat_gdt_table) + TSS_ENTRY - FIRST_RESERVED_GDT_ENTRY,
         (unsigned long)tss,
         offsetof(struct tss_struct, __cacheline_filler) - 1,
-        11);
+        DESC_TYPE_tss_busy);
 
     /* Switch to non-compat GDT (which has B bit clear) to execute LTR. */
     asm volatile (
diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index 3a48478..cdaf1e6 100644
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -394,10 +394,10 @@ void __devinit subarch_percpu_traps_init(void)
          * The 32-on-64 hypercall entry vector is only accessible from ring 1.
          * Also note that this is a trap gate, not an interrupt gate.
          */
-        _set_gate(idt_table+HYPERCALL_VECTOR, 15, 1, &compat_hypercall);
+        _set_gate(idt_table+HYPERCALL_VECTOR, DESC_TYPE_trap_gate, 1, &compat_hypercall);
 
         /* Fast trap for int80 (faster than taking the #GP-fixup path). */
-        _set_gate(idt_table+0x80, 15, 3, &int80_direct_trap);
+        _set_gate(idt_table+0x80, DESC_TYPE_trap_gate, 3, &int80_direct_trap);
     }
 
     stack_bottom = (char *)get_stack_bottom();
diff --git a/xen/include/asm-x86/desc.h b/xen/include/asm-x86/desc.h
index 4edb834..6b2094f 100644
--- a/xen/include/asm-x86/desc.h
+++ b/xen/include/asm-x86/desc.h
@@ -98,6 +98,14 @@
 
 #ifndef __ASSEMBLY__
 
+/* System Descriptor types in the GDT */
+#define DESC_TYPE_ldt       (2)
+#define DESC_TYPE_tss_avail (9)
+#define DESC_TYPE_tss_busy  (11)
+#define DESC_TYPE_call_gate (12)
+#define DESC_TYPE_irq_gate  (14)
+#define DESC_TYPE_trap_gate (15)
+
 struct desc_struct {
     u32 a, b;
 };
diff --git a/xen/include/asm-x86/ldt.h b/xen/include/asm-x86/ldt.h
index b6f7beb..4ba6d32 100644
--- a/xen/include/asm-x86/ldt.h
+++ b/xen/include/asm-x86/ldt.h
@@ -18,7 +18,7 @@ static inline void load_LDT(struct vcpu *v)
         desc = (!is_pv_32on64_vcpu(v)
                 ? this_cpu(gdt_table) : this_cpu(compat_gdt_table))
                + LDT_ENTRY - FIRST_RESERVED_GDT_ENTRY;
-        _set_tssldt_desc(desc, LDT_VIRT_START(v), ents*8-1, 2);
+        _set_tssldt_desc(desc, LDT_VIRT_START(v), ents*8-1, DESC_TYPE_ldt);
         __asm__ __volatile__ ( "lldt %%ax" : : "a" (LDT_ENTRY << 3) );
     }
 }
-- 
1.7.10.4