Implement PHYS_OFFSET mapping

src/arch/emulate.rs

@@ -20,7 +20,6 @@ impl Arch for EmulateArch {
     const PAGE_SHIFT: usize = X8664Arch::PAGE_SHIFT;
     const PAGE_ENTRY_SHIFT: usize = X8664Arch::PAGE_ENTRY_SHIFT;
     const PAGE_LEVELS: usize = X8664Arch::PAGE_LEVELS;
-    const PAGE_OFFSET: usize = X8664Arch::PAGE_OFFSET;
 
     const ENTRY_ADDRESS_SHIFT: usize = X8664Arch::ENTRY_ADDRESS_SHIFT;
     const ENTRY_FLAG_PRESENT: usize = X8664Arch::ENTRY_FLAG_PRESENT;
@@ -30,6 +29,8 @@ impl Arch for EmulateArch {
     const ENTRY_FLAG_GLOBAL: usize = X8664Arch::ENTRY_FLAG_GLOBAL;
     const ENTRY_FLAG_NO_EXEC: usize = X8664Arch::ENTRY_FLAG_NO_EXEC;
 
+    const PHYS_OFFSET: usize = X8664Arch::PHYS_OFFSET;
+
     unsafe fn init() -> &'static [MemoryArea] {
         // Create machine with PAGE_ENTRIES pages identity mapped (2 MiB on x86_64)
         // Pages over 1 MiB will be mapped writable
@@ -41,8 +42,8 @@ impl Arch for EmulateArch {
         let flags = Self::ENTRY_FLAG_WRITABLE | Self::ENTRY_FLAG_PRESENT;
         machine.write_phys::<usize>(PhysicalAddress::new(pml4), pdp | flags);
 
-        // Recursive mapping
-        machine.write_phys::<usize>(PhysicalAddress::new(pml4 + (Self::PAGE_ENTRIES - 1) * Self::PAGE_ENTRY_SIZE), pml4 | flags);
+        // PML4 index 256, set to PDP again for PHYS_OFFSET mapping
+        machine.write_phys::<usize>(PhysicalAddress::new(pml4 + 256 * Self::PAGE_ENTRY_SIZE), pdp | flags);
 
         // PDP link to PD
         let pd = pdp + Self::PAGE_SIZE;

src/arch/mod.rs

@@ -13,7 +13,6 @@ pub trait Arch {
     const PAGE_SHIFT: usize;
     const PAGE_ENTRY_SHIFT: usize;
     const PAGE_LEVELS: usize;
-    const PAGE_OFFSET: usize;
 
     const ENTRY_ADDRESS_SHIFT: usize;
     const ENTRY_FLAG_PRESENT: usize;
@@ -23,6 +22,8 @@ pub trait Arch {
     const ENTRY_FLAG_GLOBAL: usize;
     const ENTRY_FLAG_NO_EXEC: usize;
 
+    const PHYS_OFFSET: usize;
+
     const PAGE_SIZE: usize = 1 << Self::PAGE_SHIFT;
     const PAGE_OFFSET_MASK: usize = Self::PAGE_SIZE - 1;
     const PAGE_ADDRESS_SHIFT: usize = Self::PAGE_LEVELS * Self::PAGE_ENTRY_SHIFT + Self::PAGE_SHIFT;
@@ -61,6 +62,6 @@ pub trait Arch {
     unsafe fn set_table(address: PhysicalAddress);
 
     unsafe fn phys_to_virt(phys: PhysicalAddress) -> VirtualAddress {
-        VirtualAddress::new(phys.data() + Self::PAGE_OFFSET)
+        VirtualAddress::new(phys.data() + Self::PHYS_OFFSET)
     }
 }

src/arch/x86_64.rs

@@ -11,7 +11,6 @@ impl Arch for X8664Arch {
     const PAGE_SHIFT: usize = 12; // 4096 bytes
     const PAGE_ENTRY_SHIFT: usize = 9; // 512 entries, 8 bytes each
     const PAGE_LEVELS: usize = 4; // PML4, PDP, PD, PT
-    const PAGE_OFFSET: usize = Self::PAGE_NEGATIVE_MASK; // PML4 slot 256 and onwards
 
     const ENTRY_ADDRESS_SHIFT: usize = 52;
     const ENTRY_FLAG_PRESENT: usize = 1 << 0;
@@ -21,6 +20,8 @@ impl Arch for X8664Arch {
     const ENTRY_FLAG_GLOBAL: usize = 1 << 8;
     const ENTRY_FLAG_NO_EXEC: usize = 1 << 63;
 
+    const PHYS_OFFSET: usize = Self::PAGE_NEGATIVE_MASK + (Self::PAGE_ADDRESS_SIZE >> 1); // PML4 slot 256 and onwards
+
     unsafe fn init() -> &'static [MemoryArea] {
         unimplemented!()
     }
@@ -63,5 +64,7 @@ mod tests {
         assert_eq!(X8664Arch::ENTRY_ADDRESS_SIZE, 0x0010_0000_0000_0000);
         assert_eq!(X8664Arch::ENTRY_ADDRESS_MASK, 0x000F_FFFF_FFFF_F000);
         assert_eq!(X8664Arch::ENTRY_FLAGS_MASK, 0xFFF0_0000_0000_0FFF);
+
+        assert_eq!(X8664Arch::PHYS_OFFSET, 0xFFFF_8000_0000_0000);
     }
 }

src/page/table.rs

@@ -40,17 +40,16 @@ impl<A: Arch> PageTable<A> {
     }
 
     pub unsafe fn virt(&self) -> VirtualAddress {
-        // Recursive mapping
-        let mut addr = 0xFFFF_FFFF_FFFF_F000;
-        for level in (self.level + 1 .. A::PAGE_LEVELS).rev() {
-            let index = (self.base.0 >> (level * A::PAGE_ENTRY_SHIFT + A::PAGE_SHIFT)) & A::PAGE_ENTRY_MASK;
-            addr <<= A::PAGE_ENTRY_SHIFT;
-            addr |= index << A::PAGE_SHIFT;
-        }
-        VirtualAddress::new(addr)
+        A::phys_to_virt(self.phys)
 
-        // Identity mapping
-        //VirtualAddress(self.phys.0)
+        // Recursive mapping
+        // let mut addr = 0xFFFF_FFFF_FFFF_F000;
+        // for level in (self.level + 1 .. A::PAGE_LEVELS).rev() {
+        //     let index = (self.base.0 >> (level * A::PAGE_ENTRY_SHIFT + A::PAGE_SHIFT)) & A::PAGE_ENTRY_MASK;
+        //     addr <<= A::PAGE_ENTRY_SHIFT;
+        //     addr |= index << A::PAGE_SHIFT;
+        // }
+        // VirtualAddress::new(addr)
     }
 
     pub fn entry_base(&self, i: usize) -> Option<VirtualAddress> {