svsm: do not depend on nightly const_mut_refs feature

Luckily, mutable references depending on this feature can be converted
to immutable references or be removed alltogether.

The mutable pointer to a ConsoleWriter in Console can be const because
ConsoleWriter::put_byte() takes &self. On the other hand,
ImmutAfterInitRef::new_from_cell() requires using a raw pointer in a
const context, which will not work without the feature. Since it is
not in use, remove the method.

Signed-off-by: Carlos López <carlos.lopez@suse.com>

src/console.rs

@@ -15,11 +15,11 @@ pub trait ConsoleWriter {
 }
 
 pub struct Console {
-    writer: *mut dyn ConsoleWriter,
+    writer: *const dyn ConsoleWriter,
 }
 
 impl Console {
-    pub fn set(&mut self, w: *mut dyn ConsoleWriter) {
+    pub fn set(&mut self, w: *const dyn ConsoleWriter) {
         self.writer = w;
     }
 }
@@ -42,7 +42,7 @@ impl fmt::Write for Console {
 
 pub static WRITER: SpinLock<Console> = SpinLock::new(unsafe {
     Console {
-        writer: &mut DEFAULT_SERIAL_PORT,
+        writer: &DEFAULT_SERIAL_PORT,
     }
 });
 static CONSOLE_INITIALIZED: ImmutAfterInitCell<bool> = ImmutAfterInitCell::new(false);

src/lib.rs

@@ -5,7 +5,6 @@
 // Author: Nicolai Stange <nstange@suse.de>
 
 #![no_std]
-#![feature(const_mut_refs)]
 
 pub mod acpi;
 pub mod address;

src/stage2.rs

@@ -6,7 +6,7 @@
 
 #![no_std]
 #![no_main]
-#![feature(const_mut_refs, rustc_private)]
+#![feature(rustc_private)]
 
 pub mod boot_stage2;
 
@@ -102,7 +102,7 @@ fn setup_env() {
     init_percpu();
 
     unsafe {
-        WRITER.lock().set(&mut CONSOLE_SERIAL);
+        WRITER.lock().set(&CONSOLE_SERIAL);
     }
     init_console();
 

src/svsm.rs

@@ -6,7 +6,6 @@
 
 #![no_std]
 #![no_main]
-#![feature(const_mut_refs)]
 pub mod svsm_paging;
 
 extern crate alloc;

src/utils/immut_after_init.rs

@@ -183,7 +183,7 @@ pub struct ImmutAfterInitRef<'a, T: 'a> {
     #[doc(hidden)]
     ptr: ImmutAfterInitCell<*const T>,
     #[doc(hidden)]
-    _phantom: PhantomData<&'a mut &'a T>,
+    _phantom: PhantomData<&'a &'a T>,
 }
 
 impl<'a, T> ImmutAfterInitRef<'a, T> {
@@ -249,19 +249,6 @@ impl<'a, T: Copy> ImmutAfterInitRef<'a, T> {
     {
         self.ptr.init(&(*cell.data.get()).as_ptr());
     }
-
-    /// Create an initialized `ImmutAfterInitRef` instance pointing to a value
-    /// wrapped in a [`ImmutAfterInitCell`].
-    ///
-    /// * `cell` - The value to make the `ImmutAfterInitRef` to refer to. By
-    ///            convention, the referenced value must have been initialized
-    ///            already.
-    pub const fn new_from_cell(cell: &'a ImmutAfterInitCell<T>) -> Self {
-        Self {
-            ptr: ImmutAfterInitCell::new(unsafe { &*cell.data.get() }.as_ptr()),
-            _phantom: PhantomData,
-        }
-    }
 }
 
 impl<'a, T> Deref for ImmutAfterInitRef<'a, T> {