fix page table update flags

remove wrong method 'PageTableEntry::flags_mut', modify flags through
this lead to PPN being zeroed

Author: wangrunji0408

src/paging/page_table.rs

@@ -2,6 +2,7 @@ use addr::*;
 use core::fmt::{Debug, Error, Formatter};
 use core::ops::{Index, IndexMut};
 
+#[repr(C)]
 pub struct PageTable {
     entries: [PageTableEntry; ENTRY_COUNT],
 }
@@ -53,6 +54,7 @@ impl Debug for PageTable {
 }
 
 #[derive(Copy, Clone)]
+#[repr(C)]
 pub struct PageTableEntry(usize);
 
 impl PageTableEntry {
@@ -79,9 +81,6 @@ impl PageTableEntry {
         flags |= EF::ACCESSED | EF::DIRTY;
         self.0 = (frame.number() << 10) | flags.bits();
     }
-    pub fn flags_mut(&mut self) -> &mut PageTableFlags {
-        unsafe { &mut *(self as *mut _ as *mut PageTableFlags) }
-    }
 }
 
 impl Debug for PageTableEntry {

src/paging/recursive.rs

@@ -30,7 +30,7 @@ pub trait Mapper {
         flags: PageTableFlags,
     ) -> Result<MapperFlush, FlagUpdateError> {
         self.ref_entry(page).map(|e| {
-            *e.flags_mut() = flags;
+            e.set(e.frame(), flags);
             MapperFlush::new(page)
         })
     }