From bb8b94f954a559d1efac987dce1860bbb232d746 Mon Sep 17 00:00:00 2001
From: Jon Lange <jlange@microsoft.com>
Date: Tue, 28 Nov 2023 13:17:59 -0800
Subject: [PATCH] Optimize VMM creation of reserved ranges by skipping the loop
 that attempts to map pages

Signed-off-by: Jon Lange <jlange@microsoft.com>
---
 src/mm/vm/mapping/api.rs      | 11 +++++++++++
 src/mm/vm/mapping/reserved.rs |  4 ++++
 src/mm/vm/range.rs            |  5 +++++
 3 files changed, 20 insertions(+)

diff --git a/src/mm/vm/mapping/api.rs b/src/mm/vm/mapping/api.rs
index 7917d6250..3c2745a4d 100644
--- a/src/mm/vm/mapping/api.rs
+++ b/src/mm/vm/mapping/api.rs
@@ -39,6 +39,17 @@ pub trait VirtualMapping: core::fmt::Debug {
     /// Mapping size. Will always be a multiple of `VirtualMapping::page_size()`
     fn mapping_size(&self) -> usize;
 
+    /// Indicates whether the mapping has any associated data.
+    ///
+    /// # Returns
+    ///
+    /// `true' if there is associated physical data, or `false' if there is
+    /// none.
+    fn has_data(&self) -> bool {
+        // Defaults to true
+        true
+    }
+
     /// Request physical address to map for a given offset
     ///
     /// # Arguments
diff --git a/src/mm/vm/mapping/reserved.rs b/src/mm/vm/mapping/reserved.rs
index 7dcbf4266..5bd9b298b 100644
--- a/src/mm/vm/mapping/reserved.rs
+++ b/src/mm/vm/mapping/reserved.rs
@@ -51,6 +51,10 @@ impl VirtualMapping for VMReserved {
         self.size
     }
 
+    fn has_data(&self) -> bool {
+        false
+    }
+
     fn map(&self, _offset: usize) -> Option<PhysAddr> {
         None
     }
diff --git a/src/mm/vm/range.rs b/src/mm/vm/range.rs
index cf324ca6a..fa584de5d 100644
--- a/src/mm/vm/range.rs
+++ b/src/mm/vm/range.rs
@@ -159,6 +159,11 @@ impl VMR {
         let page_size = mapping.page_size();
         let shared = mapping.shared();
 
+        // Exit early if the mapping has no data.
+        if !mapping.has_data() {
+            return Ok(());
+        }
+
         while vmm_start + offset < vmm_end {
             let idx = PageTable::index::<3>(VirtAddr::from(vmm_start - rstart));
             if let Some(paddr) = mapping.map(offset) {