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Improve the VmSpace forking API

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This commit is contained in:
Zhang Junyang
2024-09-23 22:16:09 +08:00
committed by Tate, Hongliang Tian
parent d4036d1e9d
commit ac6d9256ef
6 changed files with 197 additions and 186 deletions
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48
ostd/src/mm/page_table/mod.rs
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@ -92,53 +92,29 @@ impl PageTable<UserMode> {
self.root.activate();
}
}
/// Create a cloned new page table.
///
/// This method takes a mutable cursor to the old page table that locks the
/// entire virtual address range. The caller may implement the copy-on-write
/// mechanism by first protecting the old page table and then clone it using
/// this method.
///
/// TODO: We may consider making the page table itself copy-on-write.
pub fn clone_with(
&self,
cursor: CursorMut<'_, UserMode, PageTableEntry, PagingConsts>,
) -> Self {
let root_node = cursor.leak_root_guard().unwrap();
const NR_PTES_PER_NODE: usize = nr_subpage_per_huge::<PagingConsts>();
let new_root_node = unsafe {
root_node.make_copy(
0..NR_PTES_PER_NODE / 2,
NR_PTES_PER_NODE / 2..NR_PTES_PER_NODE,
)
};
PageTable::<UserMode> {
root: new_root_node.into_raw(),
_phantom: PhantomData,
}
}
}
impl PageTable<KernelMode> {
/// Create a new user page table.
///
/// This should be the only way to create the first user page table, that is
/// to fork the kernel page table with all the kernel mappings shared.
///
/// Then, one can use a user page table to call [`fork_copy_on_write`], creating
/// other child page tables.
/// This should be the only way to create the user page table, that is to
/// duplicate the kernel page table with all the kernel mappings shared.
pub fn create_user_page_table(&self) -> PageTable<UserMode> {
let root_node = self.root.clone_shallow().lock();
let mut new_node = PageTableNode::alloc(PagingConsts::NR_LEVELS);
// Make a shallow copy of the root node in the kernel space range.
// The user space range is not copied.
const NR_PTES_PER_NODE: usize = nr_subpage_per_huge::<PagingConsts>();
let new_root_node =
unsafe { root_node.make_copy(0..0, NR_PTES_PER_NODE / 2..NR_PTES_PER_NODE) };
for i in NR_PTES_PER_NODE / 2..NR_PTES_PER_NODE {
let child = root_node.child(i, /* meaningless */ true);
if !child.is_none() {
let _ = new_node.replace_child(i, child, /* meaningless */ true);
}
}
PageTable::<UserMode> {
root: new_root_node.into_raw(),
root: new_node.into_raw(),
_phantom: PhantomData,
}
}