use treemap for vm

xernel/kernel/src/mem/mmap.rs

@@ -30,8 +30,7 @@ pub fn mmap(
 
     match flags {
         MapFlags::ANONYMOUS => {
-            let start_address = process.vm().find_next_start_address();
-            process.vm().add_entry(start_address, len, prot, flags);
+            let start_address = process.vm().create_entry_at(addr, len, prot, flags);
 
             Ok(start_address.as_u64() as isize)
         }
@@ -60,7 +59,7 @@ pub fn handle_page_fault(addr: VirtAddr, error_code: PageFaultErrorCode) -> bool
         let base_addr = addr.align_down(Size4KiB::SIZE);
         let frame = FRAME_ALLOCATOR.lock().allocate_frame::<Size4KiB>().unwrap();
 
-        let pt_flags = ptflags_from_protflags(vm_entry.prot);
+        let pt_flags = ptflags_from_protflags(vm_entry.prot, true); // TODO: don't hardcode user_accessible
         let mut pt = process.get_page_table().unwrap();
 
         pt.map::<Size4KiB>(frame, Page::from_start_address(base_addr).unwrap(), pt_flags, true);

xernel/kernel/src/mem/mod.rs

@@ -13,12 +13,12 @@ pub static HIGHER_HALF_OFFSET: Once<u64> = Once::new();
 
 pub const KERNEL_OFFSET: u64 = 0xffff_ffff_8000_0000;
 pub const HEAP_START_ADDR: usize = 0xffff_9000_0000_0000;
-// NOTE: there are 16 TB available for mmap until it overflows into the non-canonical address space
-pub const MMAP_START_ADDR: usize = 0x0000_7000_0000_0000;
 
 // NOTE: stack grows down
 pub const KERNEL_THREAD_STACK_TOP: u64 = 0xffff_a000_0000_0000;
-pub const USER_THREAD_STACK_TOP: u64 = 0x0000_ffff_ffff_f000;
+
+pub const PROCESS_END: u64 = 0x0000_ffff_ffff_f000;
+pub const PROCESS_START: u64 = 0x0000_0001_0000_0000;
 
 pub const STACK_SIZE: u64 = 0x40000;
 pub const FRAME_SIZE: u64 = 4096;

xernel/kernel/src/mem/vm.rs

@@ -1,17 +1,18 @@
-use alloc::vec::Vec;
+use alloc::collections::BTreeMap;
 use libxernel::syscall::{MapFlags, ProtectionFlags};
-use x86_64::align_up;
 use x86_64::structures::paging::PageTableFlags;
 use x86_64::{
     structures::paging::{PageSize, Size4KiB},
     VirtAddr,
 };
 
-use super::MMAP_START_ADDR;
+use crate::mem::PROCESS_END;
+
+use super::{PROCESS_START, STACK_SIZE};
 
 pub struct VmEntry {
-    start: VirtAddr,
-    length: usize,
+    pub start: VirtAddr,
+    pub length: usize,
     pub prot: ProtectionFlags,
     pub flags: MapFlags,
     // TODO: add something to represent to which file this entry belongs to
@@ -25,38 +26,136 @@ impl VmEntry {
 }
 
 pub struct Vm {
-    entries: Vec<VmEntry>,
+    entries: BTreeMap<VirtAddr, VmEntry>,
 }
 
 impl Vm {
     pub const fn new() -> Self {
-        Self { entries: Vec::new() }
+        Self {
+            entries: BTreeMap::new(),
+        }
     }
 
-    pub fn add_entry(&mut self, start: VirtAddr, length: usize, prot: ProtectionFlags, flags: MapFlags) {
-        self.entries.push(VmEntry {
+    fn add_entry(&mut self, start: VirtAddr, length: usize, prot: ProtectionFlags, flags: MapFlags) {
+        let entry = VmEntry {
             start,
             length,
             prot,
             flags,
             file: None,
-        });
+        };
+
+        self.entries.insert(start, entry);
+    }
+
+    pub fn is_available(&self, start: VirtAddr, length: usize) -> bool {
+        self.entries.iter().any(|(_, entry)| {
+            entry.start < start && entry.end() + Size4KiB::SIZE > start
+                || start + length + Size4KiB::SIZE > entry.start
+                    && (start + length + Size4KiB::SIZE).as_u64() < Size4KiB::SIZE
+        })
     }
 
-    pub fn find_next_start_address(&self) -> VirtAddr {
-        let last_entry = self.entries.last();
+    pub fn create_entry_low(&mut self, length: usize, prot: ProtectionFlags, flags: MapFlags) -> VirtAddr {
+        self.create_entry_at(VirtAddr::new(PROCESS_START), length, prot, flags)
+    }
+
+    pub fn create_entry_high(&mut self, length: usize, prot: ProtectionFlags, flags: MapFlags) -> VirtAddr {
+        let mut start_address = VirtAddr::new(PROCESS_END - length as u64);
+
+        loop {
+            if self.is_available(start_address, length) {
+                if start_address.as_u64() < PROCESS_START {
+                    panic!(
+                        "create_entry_high: {:x}(length = {}) is out of bounds",
+                        start_address, length
+                    );
+                }
+
+                self.add_entry(start_address, length, prot, flags);
+                return start_address;
+            }
 
-        if let Some(last_entry) = last_entry {
-            VirtAddr::new(align_up(last_entry.end().as_u64(), Size4KiB::SIZE))
-        } else {
-            VirtAddr::new(MMAP_START_ADDR as u64)
+            // NOTE: at the moment only a stack should be create at the high end of the process address space
+            start_address -= STACK_SIZE;
+        }
+    }
+
+    /// A new entry is created at the given address or higher
+    pub fn create_entry_at(
+        &mut self,
+        mut start: VirtAddr,
+        length: usize,
+        prot: ProtectionFlags,
+        flags: MapFlags,
+    ) -> VirtAddr {
+        if start.as_u64() + length as u64 > PROCESS_END {
+            panic!("create_entry_at: {:x}(length = {}) is out of bounds", start, length);
+        }
+
+        if !start.is_aligned(Size4KiB::SIZE) {
+            panic!("create_entry_at: {:x} is not aligned", start);
+        }
+
+        if start.as_u64() < PROCESS_START {
+            start = VirtAddr::new(PROCESS_START);
+        }
+
+        if self.is_available(start, length) {
+            self.add_entry(start, length, prot, flags);
+            return start;
+        }
+
+        let mut values_iter = self.entries.values();
+        let mut previous = values_iter.next().unwrap();
+        let current = values_iter.next();
+
+        if current.is_none() {
+            let new_start = previous.end() + Size4KiB::SIZE;
+            let new_start = new_start.align_up(Size4KiB::SIZE);
+
+            self.add_entry(new_start, length, prot, flags);
+            return new_start;
+        }
+
+        let mut current = current.unwrap();
+
+        loop {
+            if current.start - previous.end() >= length as u64 + 2 * Size4KiB::SIZE {
+                let new_start = previous.end() + Size4KiB::SIZE;
+                let new_start = new_start.align_up(Size4KiB::SIZE);
+
+                self.add_entry(new_start, length, prot, flags);
+                return new_start;
+            }
+
+            previous = current;
+            let current_opt = values_iter.next();
+
+            if current_opt.is_none() {
+                let new_start = previous.end() + Size4KiB::SIZE;
+                let new_start = new_start.align_up(Size4KiB::SIZE);
+
+                if new_start.as_u64() + length as u64 > PROCESS_END {
+                    panic!(
+                        "create_entry_at: {:x}(length = {}) is out of bounds! Vm space is exhausted",
+                        new_start, length
+                    );
+                }
+
+                self.add_entry(new_start, length, prot, flags);
+                return new_start;
+            }
+
+            current = current_opt.unwrap();
         }
     }
 
     pub fn get_entry_from_address(&self, addr: VirtAddr) -> Option<&VmEntry> {
         self.entries
             .iter()
-            .find(|entry| entry.start <= addr && entry.end() > addr)
+            .find(|(_, entry)| entry.start <= addr && entry.end() > addr)
+            .map(|(_, entry)| entry)
     }
 
     pub fn clean_up(&mut self) {
@@ -65,12 +164,15 @@ impl Vm {
     }
 }
 
-pub fn ptflags_from_protflags(flags: ProtectionFlags) -> PageTableFlags {
+pub fn ptflags_from_protflags(flags: ProtectionFlags, user_accessible: bool) -> PageTableFlags {
     let mut new_flags = PageTableFlags::PRESENT;
 
-    if flags.contains(ProtectionFlags::READ) {
-        // TODO: how to handle this??
-        todo!("PageTableFlags::READ")
+    if user_accessible {
+        new_flags |= PageTableFlags::USER_ACCESSIBLE;
+    }
+
+    if !flags.contains(ProtectionFlags::READ) {
+        // NOTE: it is not possible to remove read access from a page
     }
 
     if flags.contains(ProtectionFlags::WRITE) {

xernel/kernel/src/sched/process.rs

@@ -1,13 +1,14 @@
 use alloc::sync::Weak;
 use core::sync::atomic::{AtomicUsize, Ordering};
+use libxernel::syscall::{MapFlags, ProtectionFlags};
 use x86_64::structures::paging::{Page, PageSize, PageTableFlags, Size4KiB};
 use x86_64::VirtAddr;
 
 use crate::fs::file::File;
 use crate::fs::vnode::VNode;
 use crate::mem::frame::FRAME_ALLOCATOR;
 use crate::mem::vm::Vm;
-use crate::mem::{KERNEL_THREAD_STACK_TOP, STACK_SIZE, USER_THREAD_STACK_TOP};
+use crate::mem::{KERNEL_THREAD_STACK_TOP, STACK_SIZE};
 use crate::VFS;
 use alloc::collections::BTreeMap;
 use alloc::sync::Arc;
@@ -18,8 +19,6 @@ use libxernel::sync::{Once, Spinlock};
 use crate::mem::paging::{Pagemap, KERNEL_PAGE_MAPPER};
 use crate::sched::thread::Thread;
 
-use libxernel::syscall::{MapFlags, ProtectionFlags};
-
 /// Ongoing counter for the ProcessID
 static PROCESS_ID_COUNTER: AtomicUsize = AtomicUsize::new(0);
 
@@ -34,7 +33,6 @@ pub struct Process {
     pub threads: Vec<Arc<Spinlock<Thread>>>,
     pub fds: BTreeMap<usize, File>,
     pub kernel_thread_stack_top: usize,
-    pub user_thread_stack_top: usize,
     pub thread_id_counter: usize,
     pub vm: Vm,
     pub cwd: Arc<Spinlock<VNode>>,
@@ -58,7 +56,6 @@ impl Process {
             threads: Vec::new(),
             fds: BTreeMap::new(),
             kernel_thread_stack_top: KERNEL_THREAD_STACK_TOP as usize,
-            user_thread_stack_top: USER_THREAD_STACK_TOP as usize,
             thread_id_counter: 0,
             vm: Vm::new(),
             cwd: VFS.lock().root_node(),
@@ -85,23 +82,22 @@ impl Process {
             );
         }
 
-        self.vm.add_entry(
-            VirtAddr::new(stack_bottom as u64),
-            STACK_SIZE as usize,
-            ProtectionFlags::READ | ProtectionFlags::WRITE,
-            MapFlags::ANONYMOUS,
-        );
+        // TODO: how to unmap this page later??
+        // We can't add it to Vm because it's not in the lower half of the address space
 
         stack_top
     }
 
     pub fn new_user_stack(&mut self) -> usize {
-        let stack_top = self.user_thread_stack_top;
-        self.user_thread_stack_top -= STACK_SIZE as usize;
-        let stack_bottom = self.user_thread_stack_top;
-
-        // create guard page
-        self.user_thread_stack_top -= Size4KiB::SIZE as usize;
+        let stack_bottom = self
+            .vm
+            .create_entry_high(
+                STACK_SIZE as usize,
+                ProtectionFlags::READ | ProtectionFlags::WRITE,
+                MapFlags::ANONYMOUS,
+            )
+            .as_u64() as usize;
+        let stack_top = STACK_SIZE as usize + stack_bottom;
 
         for addr in (stack_bottom..stack_top).step_by(Size4KiB::SIZE as usize) {
             let phys_page = FRAME_ALLOCATOR.lock().allocate_frame::<Size4KiB>().unwrap();
@@ -118,13 +114,6 @@ impl Process {
             );
         }
 
-        self.vm.add_entry(
-            VirtAddr::new(stack_bottom as u64),
-            STACK_SIZE as usize,
-            ProtectionFlags::READ | ProtectionFlags::WRITE,
-            MapFlags::ANONYMOUS,
-        );
-
         stack_top
     }