vm-migration: preserve error chain

On-behalf-of: SAP philipp.schuster@sap.com
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

vm-migration/src/lib.rs

@@ -26,7 +26,11 @@ pub enum UffdError {
     Create(#[source] std::io::Error),
 
     #[error("Cannot translate GPA {gpa:#x} to host address")]
-    GpaTranslation { gpa: u64 },
+    GpaTranslation {
+        gpa: u64,
+        #[source]
+        source: vm_memory::GuestMemoryError,
+    },
 
     #[error("Failed to register region at {addr:#x}+{len:#x}")]
     Register {

vmm/src/memory_manager.rs

@@ -996,8 +996,10 @@ impl MemoryManager {
         for range in saved_regions.regions() {
             let host_addr = guest_memory
                 .get_host_address(GuestAddress(range.gpa))
-                .map_err(|_| UffdError::GpaTranslation { gpa: range.gpa })?
-                as u64;
+                .map_err(|e| UffdError::GpaTranslation {
+                    gpa: range.gpa,
+                    source: e,
+                })? as u64;
 
             let ioctls = uffd::register(uffd_fd.as_fd(), host_addr, range.length).map_err(|e| {
                 UffdError::Register {