Refactor VMRange code and fix two bugs

The first bug is that a VMRange may not be allocated to a 4KB-aligned address.
The second bug is that a VMRange may not be deallocated by its parent VMRange.

src/libos/src/prelude.rs

@@ -55,3 +55,7 @@ pub fn align_up(addr: usize, align: usize) -> usize {
 pub fn align_down(addr: usize, align: usize) -> usize {
     addr & !(align - 1)
 }
+
+pub fn unbox<T>(value: Box<T>) -> T {
+    *value
+}

src/libos/src/vm/mod.rs

@@ -3,17 +3,15 @@ use prelude::*;
 use process::{get_current, Process, ProcessRef};
 use std::fmt;
 
-// TODO: Rename VMSpace to VMUniverse
-
 #[macro_use]
 mod vm_range;
-mod process_vm;
 mod vm_area;
-mod vm_domain;
+mod process_vm;
-mod vm_space;
 
-pub use self::process_vm::ProcessVM;
 pub use self::vm_range::{VMRange, VMRangeTrait};
+pub use self::vm_area::{VMSpace, VMDomain, VMArea, VMAreaFlags, VM_AREA_FLAG_R, VM_AREA_FLAG_W, VM_AREA_FLAG_X};
+pub use self::process_vm::ProcessVM;
+
 
 // TODO: separate proc and flags
 // TODO: accept fd and offset
@@ -56,23 +54,6 @@ pub fn do_brk(addr: usize) -> Result<usize, Error> {
 
 pub const PAGE_SIZE: usize = 4096;
 
-#[derive(Debug)]
-pub struct VMSpace {
-    range: VMRange,
-    guard_type: VMGuardAreaType,
-}
-
-#[derive(Debug, Default)]
-pub struct VMDomain {
-    range: VMRange,
-}
-
-#[derive(Debug, Default)]
-pub struct VMArea {
-    range: VMRange,
-    flags: VMAreaFlags,
-}
-
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum VMGuardAreaType {
     None,
@@ -80,32 +61,13 @@ pub enum VMGuardAreaType {
     Dynamic { size: usize },
 }
 
-#[derive(Copy, Clone, Debug, Default, PartialEq)]
-pub struct VMAreaFlags(pub u32);
 
-pub const VM_AREA_FLAG_R: u32 = 0x1;
+#[derive(Clone, PartialEq, Default)]
-pub const VM_AREA_FLAG_W: u32 = 0x2;
-pub const VM_AREA_FLAG_X: u32 = 0x4;
-
-impl VMAreaFlags {
-    pub fn can_execute(&self) -> bool {
-        self.0 & VM_AREA_FLAG_X == VM_AREA_FLAG_X
-    }
-
-    pub fn can_write(&self) -> bool {
-        self.0 & VM_AREA_FLAG_W == VM_AREA_FLAG_W
-    }
-
-    pub fn can_read(&self) -> bool {
-        self.0 & VM_AREA_FLAG_R == VM_AREA_FLAG_R
-    }
-}
-
-#[derive(Clone, Copy, PartialEq, Default)]
 pub struct VMAllocOptions {
     size: usize,
     addr: VMAddrOption,
     growth: VMGrowthType,
+    description: String,
 }
 
 impl VMAllocOptions {
@@ -131,6 +93,11 @@ impl VMAllocOptions {
         self.growth = growth;
         Ok(self)
     }
+
+    pub fn description(&mut self, description: &str) -> Result<&mut Self, Error> {
+        self.description = description.to_owned();
+        Ok(self)
+    }
 }
 
 impl fmt::Debug for VMAllocOptions {

src/libos/src/vm/process_vm.rs

@@ -11,7 +11,7 @@ lazy_static! {
             (addr, size)
         };
         let vm_space = unsafe {
-            match VMSpace::new(addr, size, VMGuardAreaType::None) {
+            match VMSpace::new(addr, size, VMGuardAreaType::None, "DATA_SPACE") {
                 Ok(vm_space) => vm_space,
                 Err(_) => panic!("Failed to create a VMSpace"),
             }
@@ -27,11 +27,11 @@ extern "C" {
 #[derive(Debug, Default)]
 pub struct ProcessVM {
     //code_domain: VMDomain,
-    data_domain: VMDomain,
+    data_domain: Option<Box<VMDomain>>,
-    code_vma: VMArea,
+    code_vma: Option<Box<VMArea>>,
-    data_vma: VMArea,
+    data_vma: Option<Box<VMArea>>,
-    heap_vma: VMArea,
+    heap_vma: Option<Box<VMArea>>,
-    stack_vma: VMArea,
+    stack_vma: Option<Box<VMArea>>,
     mmap_vmas: Vec<Box<VMArea>>,
     brk: usize,
 }
@@ -44,29 +44,39 @@ impl ProcessVM {
         stack_size: usize,
         mmap_size: usize,
     ) -> Result<ProcessVM, Error> {
-        let data_domain_size = code_size + data_size + heap_size + stack_size + mmap_size;
+        // Allocate the data domain from the global data space
-        let mut data_domain = DATA_SPACE.lock().unwrap().alloc_domain(data_domain_size)?;
+        let mut data_domain = {
-
+            let data_domain_size = code_size + data_size + heap_size
-        let (code_vma, data_vma, heap_vma, stack_vma) = ProcessVM::alloc_vmas(
+                                 + stack_size + mmap_size;
-            &mut data_domain,
+            let data_domain = DATA_SPACE.lock().unwrap().alloc_domain(
-            code_size,
+                                    data_domain_size, "data_domain")?;
-            data_size,
+            data_domain
-            heap_size,
+        };
-            stack_size,
+        // Allocate vmas from the data domain
-        )?;
+        let (code_vma, data_vma, heap_vma, stack_vma) =
+            match ProcessVM::alloc_vmas(&mut data_domain, code_size,
+                                        data_size, heap_size, stack_size) {
+                Err(e) => {
+                    // Note: we need to handle error here so that we can
+                    // deallocate the data domain explictly.
+                    DATA_SPACE.lock().unwrap().dealloc_domain(data_domain);
+                    return Err(e);
+                },
+                Ok(vmas) => vmas,
+            };
         // Initial value of the program break
         let brk = heap_vma.get_start();
         // No mmapped vmas initially
         let mmap_vmas = Vec::new();
 
         let vm = ProcessVM {
-            data_domain,
+            data_domain: Some(Box::new(data_domain)),
-            code_vma,
+            code_vma: Some(Box::new(code_vma)),
-            data_vma,
+            data_vma: Some(Box::new(data_vma)),
-            heap_vma,
+            heap_vma: Some(Box::new(heap_vma)),
-            stack_vma,
+            stack_vma: Some(Box::new(stack_vma)),
-            mmap_vmas,
+            mmap_vmas: mmap_vmas,
-            brk,
+            brk: brk,
         };
         Ok(vm)
     }
@@ -79,11 +89,12 @@ impl ProcessVM {
         stack_size: usize,
     ) -> Result<(VMArea, VMArea, VMArea, VMArea), Error> {
         let mut addr = data_domain.get_start();
-
         let mut alloc_vma_continuously =
-            |addr: &mut usize, size, flags, growth| -> Result<_, Error> {
+            |addr: &mut usize, size, flags, growth, desc| -> Result<_, Error> {
                 let mut options = VMAllocOptions::new(size)?;
-                options.addr(VMAddrOption::Fixed(*addr))?.growth(growth)?;
+                options.addr(VMAddrOption::Fixed(*addr))?
+                    .growth(growth)?
+                    .description(desc)?;
                 let new_vma = data_domain.alloc_area(&options, flags)?;
                 *addr += size;
                 Ok(new_vma)
@@ -92,39 +103,39 @@ impl ProcessVM {
         let rx_flags = VMAreaFlags(VM_AREA_FLAG_R | VM_AREA_FLAG_X);
         let rw_flags = VMAreaFlags(VM_AREA_FLAG_R | VM_AREA_FLAG_W);
 
-        let code_vma = alloc_vma_continuously(&mut addr, code_size, rx_flags, VMGrowthType::Fixed)?;
+        let code_vma = alloc_vma_continuously(&mut addr, code_size, rx_flags, VMGrowthType::Fixed, "code_vma")?;
-        let data_vma = alloc_vma_continuously(&mut addr, data_size, rw_flags, VMGrowthType::Fixed)?;
+        let data_vma = alloc_vma_continuously(&mut addr, data_size, rw_flags, VMGrowthType::Fixed, "data_vma")?;
-        let heap_vma = alloc_vma_continuously(&mut addr, 0, rw_flags, VMGrowthType::Upward)?;
+        let heap_vma = alloc_vma_continuously(&mut addr, 0, rw_flags, VMGrowthType::Upward, "heap_vma")?;
         // Preserve the space for heap
         addr += heap_size;
         // After the heap is the stack
         let stack_vma =
-            alloc_vma_continuously(&mut addr, stack_size, rw_flags, VMGrowthType::Downward)?;
+            alloc_vma_continuously(&mut addr, stack_size, rw_flags, VMGrowthType::Downward, "stack_vma")?;
         Ok((code_vma, data_vma, heap_vma, stack_vma))
     }
 
     pub fn get_base_addr(&self) -> usize {
-        self.code_vma.get_start()
+        self.get_code_vma().get_start()
     }
 
     pub fn get_code_vma(&self) -> &VMArea {
-        &self.code_vma
+        &self.code_vma.as_ref().unwrap()
     }
 
     pub fn get_data_vma(&self) -> &VMArea {
-        &self.data_vma
+        &self.data_vma.as_ref().unwrap()
     }
 
     pub fn get_heap_vma(&self) -> &VMArea {
-        &self.heap_vma
+        &self.heap_vma.as_ref().unwrap()
     }
 
     pub fn get_stack_vma(&self) -> &VMArea {
-        &self.stack_vma
+        &self.stack_vma.as_ref().unwrap()
     }
 
     pub fn get_stack_top(&self) -> usize {
-        self.stack_vma.get_end()
+        self.get_stack_vma().get_end()
     }
 
     pub fn get_mmap_vmas(&self) -> &[Box<VMArea>] {
@@ -163,7 +174,8 @@ impl ProcessVM {
             alloc_options
         };
         // TODO: when failed, try to resize data_domain
-        let new_mmap_vma = self.data_domain.alloc_area(&alloc_options, flags)?;
+        let new_mmap_vma = self.get_data_domain_mut()
+            .alloc_area(&alloc_options, flags)?;
         let addr = new_mmap_vma.get_start();
         self.mmap_vmas.push(Box::new(new_mmap_vma));
         Ok(addr)
@@ -184,8 +196,8 @@ impl ProcessVM {
             mmap_vma_i.unwrap()
         };
 
-        let mut removed_mmap_vma = self.mmap_vmas.swap_remove(mmap_vma_i);
+        let removed_mmap_vma = self.mmap_vmas.swap_remove(mmap_vma_i);
-        self.data_domain.dealloc_area(&mut removed_mmap_vma);
+        self.get_data_domain_mut().dealloc_area(unbox(removed_mmap_vma));
         Ok(())
     }
 
@@ -200,43 +212,52 @@ impl ProcessVM {
     }
 
     pub fn brk(&mut self, new_brk: usize) -> Result<usize, Error> {
+        let (heap_start, heap_end) = {
+            let heap_vma = self.heap_vma.as_ref().unwrap();
+            (heap_vma.get_start(), heap_vma.get_end())
+        };
         if new_brk == 0 {
             return Ok(self.get_brk());
-        } else if new_brk < self.heap_vma.get_start() {
+        } else if new_brk < heap_start {
             return errno!(EINVAL, "New brk address is too low");
-        } else if new_brk <= self.heap_vma.get_end() {
+        } else if new_brk > heap_end {
-            self.brk = new_brk;
+            // TODO: init the memory with zeros for the expanded area
-            return Ok(new_brk);
+            let resize_options = {
+                let new_heap_end = align_up(new_brk, 4096);
+                let new_heap_size = new_heap_end - heap_start;
+                let mut options = VMResizeOptions::new(new_heap_size)?;
+                options.addr(VMAddrOption::Fixed(heap_start));
+                options
+            };
+            let heap_vma = self.heap_vma.as_mut().unwrap();
+            let data_domain = self.data_domain.as_mut().unwrap();
+            data_domain.resize_area(heap_vma, &resize_options)?;
         }
+        self.brk = new_brk;
+        return Ok(new_brk);
+    }
 
-        // TODO: init the memory with zeros for the expanded area
+    fn get_data_domain_mut(&mut self) -> &mut Box<VMDomain> {
-        let resize_options = {
+        self.data_domain.as_mut().unwrap()
-            let brk_start = self.get_brk_start();
-            let new_heap_size = align_up(new_brk, 4096) - brk_start;
-            let mut options = VMResizeOptions::new(new_heap_size)?;
-            options.addr(VMAddrOption::Fixed(brk_start));
-            options
-        };
-        self.data_domain
-            .resize_area(&mut self.heap_vma, &resize_options)?;
-        Ok(new_brk)
     }
 }
 
 impl Drop for ProcessVM {
     fn drop(&mut self) {
-        let data_domain = &mut self.data_domain;
-
         // Remove all vma from the domain
-        data_domain.dealloc_area(&mut self.code_vma);
+        {
-        data_domain.dealloc_area(&mut self.data_vma);
+            let data_domain = self.data_domain.as_mut().unwrap();
-        data_domain.dealloc_area(&mut self.heap_vma);
+            data_domain.dealloc_area(unbox(self.code_vma.take().unwrap()));
-        data_domain.dealloc_area(&mut self.stack_vma);
+            data_domain.dealloc_area(unbox(self.data_vma.take().unwrap()));
-        for mmap_vma in &mut self.mmap_vmas {
+            data_domain.dealloc_area(unbox(self.heap_vma.take().unwrap()));
-            data_domain.dealloc_area(mmap_vma);
+            data_domain.dealloc_area(unbox(self.stack_vma.take().unwrap()));
+            for mmap_vma in self.mmap_vmas.drain(..) {
+                data_domain.dealloc_area(unbox(mmap_vma));
+            }
         }
 
         // Remove the domain from its parent space
-        DATA_SPACE.lock().unwrap().dealloc_domain(data_domain);
+        DATA_SPACE.lock().unwrap().dealloc_domain(
+            unbox(self.data_domain.take().unwrap()));
     }
 }

src/libos/src/vm/vm_area.rs

@@ -1,6 +1,107 @@
 use super::*;
 
-impl super::VMArea {
+#[derive(Debug)]
+pub struct VMSpace {
+    range: VMRange,
+    guard_type: VMGuardAreaType,
+}
+
+impl_vmrange_trait_for!(VMSpace, range);
+
+impl VMSpace {
+    pub unsafe fn new(
+        addr: usize,
+        size: usize,
+        guard_type: VMGuardAreaType,
+        desc: &str,
+    ) -> Result<VMSpace, Error> {
+        let addr = align_up(addr, PAGE_SIZE);
+        let size = align_down(size, PAGE_SIZE);
+        let range = unsafe { VMRange::new(addr, addr + size, VMGrowthType::Fixed, desc)? };
+        Ok(VMSpace { range, guard_type })
+    }
+
+    pub fn get_guard_type(&self) -> VMGuardAreaType {
+        self.guard_type
+    }
+
+    pub fn alloc_domain(&mut self, size: usize, desc: &str) -> Result<VMDomain, Error> {
+        let mut options = VMAllocOptions::new(size)?;
+        options.growth(VMGrowthType::Upward)?
+            .description(desc)?;
+
+        let new_range = self.range.alloc_subrange(&options)?;
+        Ok(VMDomain { range: new_range })
+    }
+
+    pub fn dealloc_domain(&mut self, mut domain: VMDomain) {
+        self.range.dealloc_subrange(&mut domain.range)
+    }
+
+    pub fn resize_domain(&mut self, domain: &mut VMDomain, new_size: usize) -> Result<(), Error> {
+        let options = VMResizeOptions::new(new_size)?;
+        self.range.resize_subrange(&mut domain.range, &options)
+    }
+}
+
+
+#[derive(Debug)]
+pub struct VMDomain {
+    range: VMRange,
+}
+
+impl_vmrange_trait_for!(VMDomain, range);
+
+impl VMDomain {
+    pub fn alloc_area(
+        &mut self,
+        options: &VMAllocOptions,
+        flags: VMAreaFlags,
+    ) -> Result<VMArea, Error> {
+        let new_range = self.range.alloc_subrange(options)?;
+
+        // Init the memory area with all zeros
+        unsafe {
+            let mem_ptr = new_range.get_start() as *mut c_void;
+            let mem_size = new_range.get_size() as size_t;
+            memset(mem_ptr, 0 as c_int, mem_size);
+        }
+
+        Ok(VMArea {
+            range: new_range,
+            flags: flags,
+        })
+    }
+
+    pub fn dealloc_area(&mut self, mut area: VMArea) {
+        self.range.dealloc_subrange(&mut area.range)
+    }
+
+    pub fn resize_area(
+        &mut self,
+        area: &mut VMArea,
+        options: &VMResizeOptions,
+    ) -> Result<(), Error> {
+        // TODO: init memory with zeros when expanding!
+        self.range.resize_subrange(&mut area.range, options)
+    }
+}
+
+#[link(name = "sgx_tstdc")]
+extern "C" {
+    pub fn memset(p: *mut c_void, c: c_int, n: size_t) -> *mut c_void;
+}
+
+
+#[derive(Debug)]
+pub struct VMArea {
+    range: VMRange,
+    flags: VMAreaFlags,
+}
+
+impl_vmrange_trait_for!(VMArea, range);
+
+impl VMArea {
     pub fn get_flags(&self) -> &VMAreaFlags {
         &self.flags
     }
@@ -9,3 +110,25 @@ impl super::VMArea {
         &mut self.flags
     }
 }
+
+
+#[derive(Copy, Clone, Debug, Default, PartialEq)]
+pub struct VMAreaFlags(pub u32);
+
+pub const VM_AREA_FLAG_R: u32 = 0x1;
+pub const VM_AREA_FLAG_W: u32 = 0x2;
+pub const VM_AREA_FLAG_X: u32 = 0x4;
+
+impl VMAreaFlags {
+    pub fn can_execute(&self) -> bool {
+        self.0 & VM_AREA_FLAG_X == VM_AREA_FLAG_X
+    }
+
+    pub fn can_write(&self) -> bool {
+        self.0 & VM_AREA_FLAG_W == VM_AREA_FLAG_W
+    }
+
+    pub fn can_read(&self) -> bool {
+        self.0 & VM_AREA_FLAG_R == VM_AREA_FLAG_R
+    }
+}

src/libos/src/vm/vm_domain.rs

@@ -1,41 +0,0 @@
-use super::*;
-
-impl VMDomain {
-    pub fn alloc_area(
-        &mut self,
-        options: &VMAllocOptions,
-        flags: VMAreaFlags,
-    ) -> Result<VMArea, Error> {
-        let new_range = self.range.alloc_subrange(options)?;
-
-        // Init the memory area with all zeros
-        unsafe {
-            let mem_ptr = new_range.get_start() as *mut c_void;
-            let mem_size = new_range.get_size() as size_t;
-            memset(mem_ptr, 0 as c_int, mem_size);
-        }
-
-        Ok(VMArea {
-            range: new_range,
-            flags: flags,
-        })
-    }
-
-    pub fn dealloc_area(&mut self, area: &mut VMArea) {
-        self.range.dealloc_subrange(&mut area.range)
-    }
-
-    pub fn resize_area(
-        &mut self,
-        area: &mut VMArea,
-        options: &VMResizeOptions,
-    ) -> Result<(), Error> {
-        // TODO: init memory with zeros when expanding!
-        self.range.resize_subrange(&mut area.range, options)
-    }
-}
-
-#[link(name = "sgx_tstdc")]
-extern "C" {
-    pub fn memset(p: *mut c_void, c: c_int, n: size_t) -> *mut c_void;
-}

src/libos/src/vm/vm_range.rs

@@ -35,44 +35,51 @@ macro_rules! impl_vmrange_trait_for {
     };
 }
 
-impl_vmrange_trait_for!(VMRange, inner);
-impl_vmrange_trait_for!(VMSpace, range);
-impl_vmrange_trait_for!(VMDomain, range);
-impl_vmrange_trait_for!(VMArea, range);
-
 #[derive(Debug)]
 pub struct VMRange {
     inner: VMRangeInner,
-    parent_range: *const VMRange,
     sub_ranges: Option<Vec<VMRangeInner>>,
+    is_dealloced: bool,
+    description: String,
 }
 
+impl_vmrange_trait_for!(VMRange, inner);
+
 impl VMRange {
-    pub unsafe fn new(start: usize, end: usize, growth: VMGrowthType) -> Result<VMRange, Error> {
+    pub unsafe fn new(start: usize, end: usize, growth: VMGrowthType, description: &str) -> Result<VMRange, Error> {
         if start % PAGE_SIZE != 0 || end % PAGE_SIZE != 0 {
             return errno!(EINVAL, "Invalid start and/or end");
         }
         Ok(VMRange {
             inner: VMRangeInner::new(start, end, growth),
-            parent_range: 0 as *const VMRange,
             sub_ranges: None,
+            is_dealloced: false,
+            description: description.to_owned(),
         })
     }
 
     pub fn alloc_subrange(&mut self, options: &VMAllocOptions) -> Result<VMRange, Error> {
+        debug_assert!(!self.is_dealloced);
+
+        // Lazy initialize the subrange array upon the first allocation
+        if self.sub_ranges.is_none() {
+            self.init_subrange_array()?;
+        }
+
         // Find a free space that satisfies the options
         let free_space = self.look_for_free_space(options)?;
+        // Allocate a new subrange from the free space
+        let (new_subrange_idx, new_subrange_inner) = {
+            let (new_subrange_start, new_subrange_end) =
+                self.alloc_from_free_space(&free_space, options);
+            debug_assert!(free_space.contains(new_subrange_start));
+            debug_assert!(free_space.contains(new_subrange_end));
 
-        let (new_subrange_start, new_subrange_end) =
+            (free_space.index_in_subranges, VMRangeInner::new(
-            self.alloc_from_free_space(&free_space, options);
+                    new_subrange_start, new_subrange_end, options.growth))
-        debug_assert!(free_space.contains(new_subrange_start));
+        };
-        debug_assert!(free_space.contains(new_subrange_end));
-
-        let new_subrange_inner = VMRangeInner::new(new_subrange_start,
-                                                   new_subrange_end,
-                                                   options.growth);
         self.get_subranges_mut()
-            .insert(free_space.index_in_subranges, new_subrange_inner);
+            .insert(new_subrange_idx, new_subrange_inner);
 
         // Although there are two copies of the newly created VMRangeInner obj,
         // we can keep them in sync as all mutation on VMRange object must
@@ -82,29 +89,28 @@ impl VMRange {
         // other in child, in dealloc_subrange and resize_subrange functions.
         Ok(VMRange {
             inner: new_subrange_inner,
-            parent_range: self as *const VMRange,
             sub_ranges: None,
+            is_dealloced: false,
+            description: options.description.clone(),
         })
     }
 
     pub fn dealloc_subrange(&mut self, subrange: &mut VMRange) {
-        self.ensure_subrange_is_a_child(subrange);
+        debug_assert!(!self.is_dealloced);
-        if subrange.has_subranges() {
+        debug_assert!(!subrange.is_dealloced);
-            panic!("A range can only be dealloc'ed when it has no sub-ranges");
+        debug_assert!(self.sub_ranges.is_some());
-        }
 
         // Remove the sub-range
         let domain_i = self.position_subrange(subrange);
         self.get_subranges_mut().remove(domain_i);
-
         // When all sub-ranges are removed, remove the sub-range array
         if self.get_subranges().len() == 2 {
             // two sentinel sub-ranges excluded
             self.sub_ranges = None;
         }
 
-        // Mark a range as dealloc'ed
+        subrange.inner.end = subrange.inner.start;
-        subrange.mark_as_dealloced();
+        subrange.is_dealloced = true;
     }
 
     pub fn resize_subrange(
@@ -112,7 +118,9 @@ impl VMRange {
         subrange: &mut VMRange,
         options: &VMResizeOptions,
     ) -> Result<(), Error> {
-        self.ensure_subrange_is_a_child(subrange);
+        debug_assert!(!self.is_dealloced);
+        debug_assert!(!subrange.is_dealloced);
+        debug_assert!(self.sub_ranges.is_some());
 
         // Get valid parameters from options
         let new_size = options.new_size;
@@ -136,6 +144,10 @@ impl VMRange {
         }
     }
 
+    pub fn get_description(&self) -> &str {
+        &self.description
+    }
+
     fn init_subrange_array(&mut self) -> Result<(), Error> {
         // Use dummy VMRange as sentinel object at both ends to make the allocation
         // and deallocation algorithm simpler
@@ -152,11 +164,6 @@ impl VMRange {
         // TODO: reduce the complexity from O(N) to O(log(N)), where N is
         // the number of existing subranges.
 
-        // Lazy initialize the subrange array upon the first allocation
-        if !self.has_subranges() {
-            self.init_subrange_array()?;
-        }
-
         // Get valid parameters from options
         let size = options.size;
         let addr = options.addr;
@@ -267,19 +274,13 @@ impl VMRange {
             // this sub-range or neighbor sub-range needs to grow later.
             // As a simple heuristic, we put this sub-range near the
             // center between the previous and next sub-ranges.
-            free_space.start + (free_space.get_size() - size) / 2
+            let offset = align_down((free_space.get_size() - size) / 2, PAGE_SIZE);
+            free_space.start + offset
         };
 
         (addr, addr + size)
     }
 
-    fn ensure_subrange_is_a_child(&self, subrange: &VMRange) {
-        // FIXME:
-        /*if subrange.parent_range != self as *const VMRange {
-            panic!("This range does not contain the given sub-range");
-        }*/
-    }
-
     fn position_subrange(&self, subrange: &VMRange) -> usize {
         let sub_ranges = self.get_subranges();
         sub_ranges
@@ -296,10 +297,6 @@ impl VMRange {
         self.sub_ranges.as_mut().unwrap()
     }
 
-    fn has_subranges(&self) -> bool {
-        self.sub_ranges.is_some()
-    }
-
     fn shrink_subrange_to(&mut self, subrange: &mut VMRange, new_size: usize) -> Result<(), Error> {
         let subrange_i = self.position_subrange(subrange);
         let subranges = self.get_subranges_mut();
@@ -379,15 +376,6 @@ impl VMRange {
         }
         Ok(())
     }
-
-    fn mark_as_dealloced(&mut self) {
-        self.parent_range = 0 as *const VMRange;
-        self.inner.start = self.inner.end;
-    }
-
-    fn is_dealloced(&self) -> bool {
-        self.parent_range == 0 as *const VMRange
-    }
 }
 
 impl PartialOrd for VMRange {
@@ -404,29 +392,15 @@ impl PartialEq for VMRange {
 
 impl Drop for VMRange {
     fn drop(&mut self) {
-        if !self.is_dealloced() {
+        if !self.is_dealloced {
-            println!("VMRange::drop::panic1");
             panic!("A range must be dealloc'ed before drop");
         }
-        if self.has_subranges() {
-            println!("VMRange::drop::panic2");
-            panic!("All sub-ranges must be removed explicitly before drop");
-        }
     }
 }
 
 unsafe impl Send for VMRange {}
 unsafe impl Sync for VMRange {}
 
-impl Default for VMRange {
-    fn default() -> VMRange {
-        VMRange {
-            inner: VMRangeInner::new(0, 0, VMGrowthType::Fixed),
-            parent_range: 0 as *const VMRange,
-            sub_ranges: None,
-        }
-    }
-}
 
 #[derive(Clone, Copy)]
 pub struct VMRangeInner {
@@ -437,6 +411,8 @@ pub struct VMRangeInner {
 
 impl VMRangeInner {
     pub fn new(start: usize, end: usize, growth: VMGrowthType) -> VMRangeInner {
+        debug_assert!(start % PAGE_SIZE == 0);
+        debug_assert!(end % PAGE_SIZE == 0);
         VMRangeInner {
             start: start,
             end: end,

src/libos/src/vm/vm_space.rs

@@ -1,33 +0,0 @@
-use super::*;
-
-impl VMSpace {
-    pub unsafe fn new(
-        addr: usize,
-        size: usize,
-        guard_type: VMGuardAreaType,
-    ) -> Result<VMSpace, Error> {
-        let range = unsafe { VMRange::new(addr, addr + size, VMGrowthType::Fixed)? };
-        Ok(VMSpace { range, guard_type })
-    }
-
-    pub fn get_guard_type(&self) -> VMGuardAreaType {
-        self.guard_type
-    }
-
-    pub fn alloc_domain(&mut self, size: usize) -> Result<VMDomain, Error> {
-        let mut options = VMAllocOptions::new(size)?;
-        options.growth(VMGrowthType::Upward)?;
-
-        let new_range = self.range.alloc_subrange(&options)?;
-        Ok(VMDomain { range: new_range })
-    }
-
-    pub fn dealloc_domain(&mut self, domain: &mut VMDomain) {
-        self.range.dealloc_subrange(&mut domain.range)
-    }
-
-    pub fn resize_domain(&mut self, domain: &mut VMDomain, new_size: usize) -> Result<(), Error> {
-        let options = VMResizeOptions::new(new_size)?;
-        self.range.resize_subrange(&mut domain.range, &options)
-    }
-}