wip: sidecar: sync RAX from intercept message in handle_io_port_exit

openhcl/sidecar/src/arch/x86_64/vp.rs

@@ -259,7 +259,7 @@ fn run_vp(globals: &mut VpGlobals, command_page: &mut CommandPage, cpu_status: &
 
     let mut intercept = false;
     while cpu_status.load(Relaxed) != CpuStatus::STOP.0 {
-        match run_vp_once(command_page) {
+        match run_vp_once(command_page, globals.register_page_mapped) {
             Ok(true) => {
                 intercept = true;
                 break;
@@ -276,7 +276,7 @@ fn run_vp(globals: &mut VpGlobals, command_page: &mut CommandPage, cpu_status: &
     .unwrap(); // PANIC: will not panic, since sizeof(RunVpResponse) is 1, whereas the buffer is statically declared as 16 bytes long.
 }
 
-fn run_vp_once(command_page: &mut CommandPage) -> Result<bool, ()> {
+fn run_vp_once(command_page: &mut CommandPage, register_page_mapped: bool) -> Result<bool, ()> {
     let cpu_context = &mut command_page.cpu_context;
     // Write rax and rcx to the VP assist page.
     //
@@ -329,6 +329,16 @@ fn run_vp_once(command_page: &mut CommandPage) -> Result<bool, ()> {
             let intercept_message =
                 unsafe { &*addr_of!((*addr_space::assist_page()).intercept_message) };
             command_page.intercept_message = *intercept_message;
+
+            // Sync guest GP/XMM from the register page; cpu_context
+            // values are stale (VTL2 round-tripped on re-entry).
+            if register_page_mapped {
+                // SAFETY: the register page is mapped and not concurrently modified.
+                let reg = unsafe { &*addr_space::register_page() };
+                let xmm = reg.xmm.as_bytes().as_chunks::<16>().0;
+                command_page.cpu_context.gps = reg.gp_registers;
+                command_page.cpu_context.fx_state.xmm[..xmm.len()].copy_from_slice(xmm);
+            }
             Ok(true)
         }
         entry_reason => {