x86/pv: Factor out the calculation of LDT/GDT descriptor pointers

Rather than opencoding it in two places.  While only used in the PV emulation
code, this helper is in principle usable anywhere in the hypervisor.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/pv/emul-gate-op.c b/xen/arch/x86/pv/emul-gate-op.c
index 0f89c91dff9b19fae24ba056cc54d4e82c25daf8..14ce95e26eb5cae1a701d2f87d440944fd853e6d 100644 (file)
--- a/xen/arch/x86/pv/emul-gate-op.c
+++ b/xen/arch/x86/pv/emul-gate-op.c
@@ -54,11 +54,8 @@ static int read_gate_descriptor(unsigned int gate_sel,
                                 unsigned int *ar)
 {
     struct desc_struct desc;
-    const struct desc_struct *pdesc;
+    const struct desc_struct *pdesc = gdt_ldt_desc_ptr(gate_sel);
 
-    pdesc = (const struct desc_struct *)
-        (!(gate_sel & 4) ? GDT_VIRT_START(v) : LDT_VIRT_START(v))
-        + (gate_sel >> 3);
     if ( (gate_sel < 4) ||
          ((gate_sel >= FIRST_RESERVED_GDT_BYTE) && !(gate_sel & 4)) ||
          __get_user(desc, pdesc) )

diff --git a/xen/arch/x86/pv/emulate.c b/xen/arch/x86/pv/emulate.c
index 5750c7699b52d6be5333770c694e46b064c067cc..1b609117a3a257637fef126c37702bf01050f346 100644 (file)
--- a/xen/arch/x86/pv/emulate.c
+++ b/xen/arch/x86/pv/emulate.c
@@ -33,11 +33,7 @@ int pv_emul_read_descriptor(unsigned int sel, const struct vcpu *v,
 
     if ( sel < 4)
         desc.b = desc.a = 0;
-    else if ( __get_user(desc,
-                         (const struct desc_struct *)(!(sel & 4)
-                                                      ? GDT_VIRT_START(v)
-                                                      : LDT_VIRT_START(v))
-                         + (sel >> 3)) )
+    else if ( __get_user(desc, gdt_ldt_desc_ptr(sel)) )
         return 0;
     if ( !insn_fetch )
         desc.b &= ~_SEGMENT_L;

diff --git a/xen/arch/x86/pv/emulate.h b/xen/arch/x86/pv/emulate.h
index 656c12f62de90bd970e3cbc0119a6700c4e23a54..9d587947f5aba1fae6ee88fcf5ad2ef88558f58c 100644 (file)
--- a/xen/arch/x86/pv/emulate.h
+++ b/xen/arch/x86/pv/emulate.h
@@ -1,6 +1,7 @@
 #ifndef __PV_EMULATE_H__
 #define __PV_EMULATE_H__
 
+#include <asm/processor.h>
 #include <asm/x86_emulate.h>
 
 int pv_emul_read_descriptor(unsigned int sel, const struct vcpu *v,
@@ -16,4 +17,14 @@ static inline int pv_emul_is_mem_write(const struct x86_emulate_state *state,
                                               : X86EMUL_UNHANDLEABLE;
 }
 
+/* Return a pointer to the GDT/LDT descriptor referenced by sel. */
+static inline const struct desc_struct *gdt_ldt_desc_ptr(unsigned int sel)
+{
+    const struct vcpu *curr = current;
+    const struct desc_struct *tbl = (void *)
+        ((sel & X86_XEC_TI) ? LDT_VIRT_START(curr) : GDT_VIRT_START(curr));
+
+    return &tbl[sel >> 3];
+}
+
 #endif /* __PV_EMULATE_H__ */