rebinding: populate UTF-8 reason string on SPDM error paths

The non-SPDM rebinding_old_prepare / rebinding_new_prepare populate the
VMM ReportStatus reason buffer (data: &mut Vec<u8>) on transport
failures, gated by #[cfg(feature = "vmcall-raw")]. The SPDM-featured
counterparts had the parameter spelled _data and never wrote to it, so
GHCI 1.5 ReportStatus (p. 47-48, Tables 3-55/3-56) had no diagnostic
payload when an SPDM rebind failed.

Mirror the non-SPDM pattern at the three SPDM error sites:

  * spdm_requester / spdm_responder transport setup failure
  * with_timeout timeout error around spdm_requester_rebind_old /
    spdm_responder_rebind_new
  * the SPDM rebind operation itself

Each .map_err closure now pushes a one-line UTF-8 reason string
(operation name, MigrationResult variant, migration ID in hex) into
data, gated by #[cfg(feature = "vmcall-raw")] to match the non-SPDM
RA-TLS arms. log::error! calls are preserved verbatim.

No behavior change with vmcall-raw off: data is unused (same warning as
the existing non-SPDM functions on that configuration).

Signed-off-by: Stanislaw Grams <stanislaw.grams@intel.com>

Author: sgrams

src/migtd/src/migration/rebinding.rs

@@ -177,13 +177,21 @@ pub async fn start_rebinding(
 pub async fn rebinding_old_prepare(
     transport: TransportType,
     info: &MigtdMigrationInformation,
-    _data: &mut Vec<u8>,
+    data: &mut Vec<u8>,
     #[cfg(feature = "policy_v2")] remote_policy: Vec<u8>,
 ) -> Result<(), MigrationResult> {
     use core::ops::DerefMut;
 
     const SPDM_TIMEOUT: Duration = Duration::from_secs(60); // 60 seconds
     let (mut spdm_requester, device_io_ref) = spdm::spdm_requester(transport).map_err(|_e| {
+        #[cfg(feature = "vmcall-raw")]
+        data.extend_from_slice(
+            &format!(
+                "Error: rebinding_old_prepare(): Failed in spdm_requester transport. Migration ID: {:x}\n",
+                info.mig_request_id,
+            )
+            .into_bytes(),
+        );
         log::error!(
             "rebinding: Failed in spdm_requester transport. Migration ID: {}\n",
             info.mig_request_id
@@ -201,13 +209,29 @@ pub async fn rebinding_old_prepare(
     )
     .await
     .map_err(|e| {
+        #[cfg(feature = "vmcall-raw")]
+        data.extend_from_slice(
+            &format!(
+                "Error: rebinding_old_prepare(): spdm_requester_rebind_old timed out ({:?}). Migration ID: {:x}\n",
+                e, info.mig_request_id,
+            )
+            .into_bytes(),
+        );
         log::error!(
             "rebinding: spdm_requester_rebind_old timeout error: {:?}\n",
             e
         );
         e
     })?
     .map_err(|e| {
+        #[cfg(feature = "vmcall-raw")]
+        data.extend_from_slice(
+            &format!(
+                "Error: rebinding_old_prepare(): spdm_requester_rebind_old failed ({:?}). Migration ID: {:x}\n",
+                e, info.mig_request_id,
+            )
+            .into_bytes(),
+        );
         log::error!("rebinding: spdm_requester_rebind_old error: {:?}\n", e);
         e
     })?;
@@ -223,13 +247,21 @@ pub async fn rebinding_old_prepare(
 pub async fn rebinding_new_prepare(
     transport: TransportType,
     info: &MigtdMigrationInformation,
-    _data: &mut Vec<u8>,
+    data: &mut Vec<u8>,
     #[cfg(feature = "policy_v2")] remote_policy: Vec<u8>,
 ) -> Result<(), MigrationResult> {
     use core::ops::DerefMut;
 
     const SPDM_TIMEOUT: Duration = Duration::from_secs(60); // 60 seconds
     let (mut spdm_responder, device_io_ref) = spdm::spdm_responder(transport).map_err(|_e| {
+        #[cfg(feature = "vmcall-raw")]
+        data.extend_from_slice(
+            &format!(
+                "Error: rebinding_new_prepare(): Failed in spdm_responder transport. Migration ID: {:x}\n",
+                info.mig_request_id,
+            )
+            .into_bytes(),
+        );
         log::error!(
             "rebinding: Failed in spdm_responder transport. Migration ID: {}\n",
             info.mig_request_id
@@ -248,13 +280,29 @@ pub async fn rebinding_new_prepare(
     )
     .await
     .map_err(|e| {
+        #[cfg(feature = "vmcall-raw")]
+        data.extend_from_slice(
+            &format!(
+                "Error: rebinding_new_prepare(): spdm_responder_rebind_new timed out ({:?}). Migration ID: {:x}\n",
+                e, info.mig_request_id,
+            )
+            .into_bytes(),
+        );
         log::error!(
             "rebinding: spdm_responder_rebind_new timeout error: {:?}\n",
             e
         );
         e
     })?
     .map_err(|e| {
+        #[cfg(feature = "vmcall-raw")]
+        data.extend_from_slice(
+            &format!(
+                "Error: rebinding_new_prepare(): spdm_responder_rebind_new failed ({:?}). Migration ID: {:x}\n",
+                e, info.mig_request_id,
+            )
+            .into_bytes(),
+        );
         log::error!("rebinding: spdm_responder_rebind_new error: {:?}\n", e);
         e
     })?;