VMX: ensure MSR index enum and array remain in sync

... by using dedicated initializers. Also add an ASSERT() to make sure
unintentional addition of holes to the array gets noticed. Ditch
MSR_INDEX_SIZE as redundant with VMX_MSR_COUNT.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -321,20 +321,23 @@ static void vmx_vcpu_destroy(struct vcpu
 
 static DEFINE_PER_CPU(struct vmx_msr_state, host_msr_state);
 
-static const u32 msr_index[] =
+static const u32 msr_index[VMX_MSR_COUNT] =
 {
-    MSR_LSTAR, MSR_STAR, MSR_SYSCALL_MASK
+    [VMX_INDEX_MSR_LSTAR]        = MSR_LSTAR,
+    [VMX_INDEX_MSR_STAR]         = MSR_STAR,
+    [VMX_INDEX_MSR_SYSCALL_MASK] = MSR_SYSCALL_MASK
 };
 
-#define MSR_INDEX_SIZE (ARRAY_SIZE(msr_index))
-
 void vmx_save_host_msrs(void)
 {
     struct vmx_msr_state *host_msr_state = &this_cpu(host_msr_state);
-    int i;
+    unsigned int i;
 
-    for ( i = 0; i < MSR_INDEX_SIZE; i++ )
+    for ( i = 0; i < VMX_MSR_COUNT; i++ )
+    {
+        ASSERT(msr_index[i]);
         rdmsrl(msr_index[i], host_msr_state->msrs[i]);
+    }
 }
 
 #define WRITE_MSR(address) do {                                         \