x86/HVM: fix x2APIC APIC_ID read emulation

APIC and x2APIC have different format for APIC_ID register. Need
translation.

Signed-off-by: Zhenguo Wang <wangzhenguo@xxxxxxxxxx>
Signed-off-by: Xiaowei Yang <xiaowei.yang@xxxxxxxxxx>

Convert code to use switch(), fixing coding style issue at once, and
use GET_xAPIC_ID() on the value read instead of VLAPIC_ID() (reading
the field again).

In the course of this also properly reject both read and writes on the
non-existing MSR corresponding to APIC_ICR2.

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

--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -582,8 +582,19 @@ int hvm_x2apic_msr_read(struct vcpu *v, 
         return 1;
 
     vlapic_read_aligned(vlapic, offset, &low);
-    if ( offset == APIC_ICR )
+    switch ( offset )
+    {
+    case APIC_ID:
+        low = GET_xAPIC_ID(low);
+        break;
+
+    case APIC_ICR:
         vlapic_read_aligned(vlapic, APIC_ICR2, &high);
+        break;
+
+    case APIC_ICR2:
+        return 1;
+    }
 
     *msr_content = (((uint64_t)high) << 32) | low;
     return 0;
@@ -837,11 +848,17 @@ int hvm_x2apic_msr_write(struct vcpu *v,
     if ( !vlapic_x2apic_mode(vlapic) )
         return X86EMUL_UNHANDLEABLE;
 
-    if ( offset == APIC_ICR )
+    switch ( offset )
     {
-        int rc = vlapic_reg_write(v, APIC_ICR2, (uint32_t)(msr_content >> 32));
+        int rc;
+
+    case APIC_ICR:
+        rc = vlapic_reg_write(v, APIC_ICR2, (uint32_t)(msr_content >> 32));
         if ( rc )
             return rc;
+
+    case APIC_ICR2:
+        return X86EMUL_UNHANDLEABLE;
     }
 
     return vlapic_reg_write(v, offset, (uint32_t)msr_content);