Add missing IDT entry #HV (vector 28)

Currently the InterruptDescriptorTable is missing entry with vector number
28, #HV. More information at AMD's APM Volume 2, subsection 8.2.21. See
issue #377.

Signed-off-by: Carlos Bilbao <[email protected]>

Author: Zildj1an

src/structures/idt.rs

@@ -340,8 +340,25 @@ pub struct InterruptDescriptorTable {
     /// vector nr. 20
     pub virtualization: Entry<HandlerFunc>,
 
-    /// vector nr. 21-28
-    reserved_2: [Entry<HandlerFunc>; 8],
+    /// vector nr. 21-27
+    reserved_2: [Entry<HandlerFunc>; 7],
+
+    /// The Hypervisor Injection Exception (`#HV`) is injected by a hypervisor
+    /// as a doorbell to inform an `SEV-SNP` enabled guest running with the
+    /// `Restricted Injection` feature of events to be processed.
+    ///
+    /// `SEV-SNP` stands for the _"Secure Nested Paging"_ feature of the _"AMD
+    /// Secure Encrypted Virtualization"_  technology. The `Restricted
+    /// Injection` feature disables all hypervisor-based interrupt queuing
+    /// and event injection of all vectors except #HV.
+    ///
+    /// The `#HV` exception is a benign exception and can only be injected as
+    /// an exception and without an error code. `SEV-SNP` enabled guests are
+    /// expected to communicate with the hypervisor about events via a
+    /// software-managed para-virtualization interface.
+    ///
+    /// The vector number of the ``#HV`` exception is 28.
+    pub hv_injection_exception: Entry<HandlerFunc>,
 
     /// The VMM Communication Exception (`#VC`) is always generated by hardware when an `SEV-ES`
     /// enabled guest is running and an `NAE` event occurs.
@@ -436,7 +453,8 @@ impl InterruptDescriptorTable {
             machine_check: Entry::missing(),
             simd_floating_point: Entry::missing(),
             virtualization: Entry::missing(),
-            reserved_2: [Entry::missing(); 8],
+            reserved_2: [Entry::missing(); 7],
+            hv_injection_exception: Entry::missing(),
             vmm_communication_exception: Entry::missing(),
             security_exception: Entry::missing(),
             reserved_3: Entry::missing(),