mm/alloc: implement Allocator for SvsmAllocator

In order to be used along with the new TryBox type, an allocator must
implement the Allocator trait, so implement it for the current global
allocator.

Signed-off-by: Carlos López <[email protected]>

src/mm/alloc.rs

@@ -5,6 +5,7 @@
 // Author: Joerg Roedel <[email protected]>
 
 use crate::address::{Address, PhysAddr, VirtAddr};
+use crate::alloc::{Allocator, TryAllocError};
 use crate::error::SvsmError;
 #[cfg(any(test, fuzzing))]
 use crate::locking::LockGuard;
@@ -14,7 +15,7 @@ use crate::types::{PAGE_SHIFT, PAGE_SIZE};
 use crate::utils::{align_down, align_up, zero_mem_region};
 use core::alloc::{GlobalAlloc, Layout};
 use core::mem::size_of;
-use core::ptr;
+use core::ptr::{self, NonNull};
 use log;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -1287,6 +1288,31 @@ unsafe impl GlobalAlloc for SvsmAllocator {
     }
 }
 
+unsafe impl Allocator for SvsmAllocator {
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, TryAllocError> {
+        match layout.size() {
+            0 => Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)),
+            size => {
+                // SAFETY: size is nonzero
+                let raw_ptr = unsafe { self.alloc(layout) };
+                // FIXME: find a way to return a more correct error here. At
+                // some point we must reconcile AllocError and
+                // TryAllocError.
+                let ptr = NonNull::new(raw_ptr).ok_or(TryAllocError::OutOfMemory)?;
+                Ok(NonNull::slice_from_raw_parts(ptr, size))
+            }
+        }
+    }
+
+    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
+        // SAFETY: `layout` is non-zero in size,
+        // other conditions must be upheld by the caller
+        if layout.size() != 0 {
+            self.dealloc(ptr.as_ptr(), layout)
+        }
+    }
+}
+
 #[cfg_attr(any(target_os = "none"), global_allocator)]
 #[cfg_attr(not(target_os = "none"), allow(dead_code))]
 static ALLOCATOR: SvsmAllocator = SvsmAllocator::new();