x86/hvm: Add get_shadow_gs_base() wrapper function

Add a wrapper function to the HVM function table that returns the
shadow GS base.

Signed-off-by: Aravindh Puthiyaparambil <aravindh@virtuata.com>
Committed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/svm/svm.c

@@ -645,6 +645,11 @@ static void svm_set_segment_register(struct vcpu *v, enum x86_segment seg,
         svm_vmload(vmcb);
 }
 
+static unsigned long svm_get_shadow_gs_base(struct vcpu *v)
+{
+    return v->arch.hvm_svm.vmcb->kerngsbase;
+}
+
 static int svm_set_guest_pat(struct vcpu *v, u64 gpat)
 {
     struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
@@ -1990,6 +1995,7 @@ static struct hvm_function_table __read_mostly svm_function_table = {
     .guest_x86_mode       = svm_guest_x86_mode,
     .get_segment_register = svm_get_segment_register,
     .set_segment_register = svm_set_segment_register,
+    .get_shadow_gs_base   = svm_get_shadow_gs_base,
     .update_host_cr3      = svm_update_host_cr3,
     .update_guest_cr      = svm_update_guest_cr,
     .update_guest_efer    = svm_update_guest_efer,

xen/arch/x86/hvm/vmx/vmx.c

@@ -942,6 +942,15 @@ static void vmx_set_segment_register(struct vcpu *v, enum x86_segment seg,
     vmx_vmcs_exit(v);
 }
 
+static unsigned long vmx_get_shadow_gs_base(struct vcpu *v)
+{
+#ifdef __x86_64__
+    return v->arch.hvm_vmx.shadow_gs;
+#else
+    return 0;
+#endif
+}
+
 static int vmx_set_guest_pat(struct vcpu *v, u64 gpat)
 {
     if ( !cpu_has_vmx_pat || !paging_mode_hap(v->domain) )
@@ -1522,6 +1531,7 @@ static struct hvm_function_table __read_mostly vmx_function_table = {
     .guest_x86_mode       = vmx_guest_x86_mode,
     .get_segment_register = vmx_get_segment_register,
     .set_segment_register = vmx_set_segment_register,
+    .get_shadow_gs_base   = vmx_get_shadow_gs_base,
     .update_host_cr3      = vmx_update_host_cr3,
     .update_guest_cr      = vmx_update_guest_cr,
     .update_guest_efer    = vmx_update_guest_efer,

xen/include/asm-x86/hvm/hvm.h

@@ -106,6 +106,7 @@ struct hvm_function_table {
                                  struct segment_register *reg);
     void (*set_segment_register)(struct vcpu *v, enum x86_segment seg,
                                  struct segment_register *reg);
+    unsigned long (*get_shadow_gs_base)(struct vcpu *v);
 
     /* 
      * Re-set the value of CR3 that Xen runs on when handling VM exits.
@@ -305,6 +306,11 @@ hvm_set_segment_register(struct vcpu *v, enum x86_segment seg,
     hvm_funcs.set_segment_register(v, seg, reg);
 }
 
+static inline unsigned long hvm_get_shadow_gs_base(struct vcpu *v)
+{
+    return hvm_funcs.get_shadow_gs_base(v);
+}
+
 #define is_viridian_domain(_d)                                             \
  (is_hvm_domain(_d) && ((_d)->arch.hvm_domain.params[HVM_PARAM_VIRIDIAN]))