Switch to a bump allocator for user virtual memory allocations

src/virtual_memory.rs

@@ -32,6 +32,7 @@ pub struct AddressSpace {
     pub alloc_force_user: bool,
     pub mapper: OffsetPageTable<'static>,
     bytes_allocated: AtomicUsize,
+    bump_base: Page,
 }
 
 impl fmt::Debug for AddressSpace {
@@ -196,6 +197,7 @@ pub static KERNEL_SPACE: Lazy<ASpaceMutex> = Lazy::new(|| {
     }
     let mut kernel_space = AddressSpace::new_with_addr(table);
     kernel_space.is_kernel = true;
+    kernel_space.bump_base = KERNEL_PAGE_RANGE.start;
     let l4_virt = VirtAddr::from_ptr(ptr::from_ref(kernel_space.mapper.level_4_table()));
     #[expect(
         clippy::unwrap_used,
@@ -251,6 +253,7 @@ impl AddressSpace {
             alloc_force_user: false,
             is_kernel: false,
             bytes_allocated: AtomicUsize::new(0),
+            bump_base: USER_PAGE_RANGE.start,
         }
     }
 
@@ -379,6 +382,9 @@ impl AddressSpace {
             PhysFrame::from_start_address_unchecked(PhysAddr::new(0x000F_FFFF_FFFF_F000))
         };
         self.check_request_valid(page, num_pages)?;
+        if self.bump_base < page + u64(num_pages) {
+            self.bump_base = page + u64(num_pages);
+        }
         #[expect(
             clippy::arithmetic_side_effects,
             reason = "This is the maximum physical frame, so there is no way the subtraction can underflow"
@@ -455,6 +461,9 @@ impl AddressSpace {
         flags: PageTableFlags,
     ) -> Result<*mut u8, PagingError> {
         self.check_request_valid(page, num_pages)?;
+        if self.bump_base < page + u64(num_pages) {
+            self.bump_base = page + u64(num_pages);
+        }
         #[expect(
             clippy::arithmetic_side_effects,
             reason = "check_request_valid guarentees this won't overflow"
@@ -544,7 +553,8 @@ impl AddressSpace {
         num_pages: usize,
         flags: PageTableFlags,
     ) -> Result<*mut u8, PagingError> {
-        unsafe { self.map_to(self.find_free_pages(num_pages)?, phys_frame, num_pages, flags) }
+        let start_page = self.find_free_pages(num_pages)?;
+        unsafe { self.map_to(start_page, phys_frame, num_pages, flags) }
     }
 
     /// Maps new virtual pages to new physical memory and returns the starting address.
@@ -555,9 +565,10 @@ impl AddressSpace {
         num_pages: usize,
         flags: PageTableFlags,
     ) -> Result<*mut u8, PagingError> {
+        let start_page = self.find_free_pages(num_pages)?;
         // SAFETY: &mut aliasing is prevented by using free physical frames, and uninitialized
         // values are prevented by using free virtual pages.
-        let ptr = unsafe { self.map(self.find_free_pages(num_pages)?, num_pages, flags)? };
+        let ptr = unsafe { self.map(start_page, num_pages, flags)? };
         self.record_alloc(num_pages * 4096);
         Ok(ptr)
     }
@@ -571,10 +582,10 @@ impl AddressSpace {
         num_pages: usize,
         flags: PageTableFlags,
     ) -> Result<(*mut u8, u64), PagingError> {
+        let start_page = self.find_free_pages(num_pages)?;
         // SAFETY: &mut aliasing is prevented by using free physical frames, and uninitialized
         // values are prevented by using free virtual pages.
-        let ptr =
-            unsafe { self.map_cont_phys(self.find_free_pages(num_pages)?, num_pages, flags)? };
+        let ptr = unsafe { self.map_cont_phys(start_page, num_pages, flags)? };
         self.record_alloc(num_pages * 4096);
         Ok(ptr)
     }
@@ -602,6 +613,9 @@ impl AddressSpace {
         flags: PageTableFlags,
     ) -> Result<*mut u8, PagingError> {
         self.check_request_valid(page, num_pages)?;
+        if self.bump_base < page + u64(num_pages) {
+            self.bump_base = page + u64(num_pages);
+        }
         assert!(!self.alloc_force_user);
         #[expect(
             clippy::arithmetic_side_effects,
@@ -733,7 +747,8 @@ impl AddressSpace {
     }
 
     /// Finds a range of free pages and returns the starting page
-    fn find_free_pages(&self, num_pages: usize) -> Result<Page, PagingError> {
+    fn find_free_pages(&mut self, num_pages: usize) -> Result<Page, PagingError> {
+        if self.is_kernel {
             if num_pages == 0 {
                 return Err(PagingError::PageAllocationFailed);
             }
@@ -760,6 +775,13 @@ impl AddressSpace {
                 };
             }
             Err(PagingError::PageAllocationFailed)
+        } else if USER_PAGE_RANGE.end - self.bump_base < u64(num_pages) {
+            Err(PagingError::PageAllocationFailed)
+        } else {
+            let old_base = self.bump_base;
+            self.bump_base += u64(num_pages);
+            Ok(old_base)
+        }
     }
 
     pub fn record_alloc(&self, size: usize) {