ghcb: move shutdown code into Drop impl

Now that the shutdown code is only called from the Drop impl we might
as well move it in there. This also makes it impossible to call
shutdown more than once (or to call shutdown and the Drop the
GhcbPage).

Signed-off-by: Tom Dohrmann <erbse.13@gmx.de>

kernel/src/sev/ghcb.rs

@@ -162,7 +162,28 @@ impl GhcbPage {
 
 impl Drop for GhcbPage {
     fn drop(&mut self) {
-        self.0.shutdown().expect("Could not shut down GHCB");
+        let vaddr = self.0.vaddr();
+        let paddr = virt_to_phys(vaddr);
+
+        // Re-encrypt page
+        this_cpu()
+            .get_pgtable()
+            .set_encrypted_4k(vaddr)
+            .expect("Could not re-encrypt page");
+
+        // Unregister GHCB PA
+        register_ghcb_gpa_msr(PhysAddr::null()).expect("Could not unregister GHCB");
+
+        // Ask the hypervisor to change the page back to the private page state.
+        validate_page_msr(paddr).expect("Could not change page state");
+
+        // Make page guest-valid
+        pvalidate(vaddr, PageSize::Regular, PvalidateOp::Valid).expect("Could not pvalidate page");
+
+        // Needs guarding for Stage2 GHCB
+        if valid_bitmap_valid_addr(paddr) {
+            valid_bitmap_set_valid_4k(paddr);
+        }
     }
 }
 
@@ -313,30 +334,6 @@ impl GHCB {
         Ok(register_ghcb_gpa_msr(paddr)?)
     }
 
-    pub fn shutdown(&self) -> Result<(), SvsmError> {
-        let vaddr = VirtAddr::from(ptr::from_ref(self));
-        let paddr = virt_to_phys(vaddr);
-
-        // Re-encrypt page
-        this_cpu().get_pgtable().set_encrypted_4k(vaddr)?;
-
-        // Unregister GHCB PA
-        register_ghcb_gpa_msr(PhysAddr::null())?;
-
-        // Make page guest-invalid
-        validate_page_msr(paddr)?;
-
-        // Make page guest-valid
-        pvalidate(vaddr, PageSize::Regular, PvalidateOp::Valid)?;
-
-        // Needs guarding for Stage2 GHCB
-        if valid_bitmap_valid_addr(paddr) {
-            valid_bitmap_set_valid_4k(paddr);
-        }
-
-        Ok(())
-    }
-
     pub fn clear(&self) {
         // Clear valid bitmap
         self.valid_bitmap[0].store(0, Ordering::SeqCst);