Remove read/write flags from common PDE flags.

RISC-V convention marks PDE with no read/write/execute, so we can't have none of this flags set there. Remove their setting from PDE handling code and instead set them as appropriate in arch-specific defaults.

Also enable both readonly and readwrite flags to be non-zero (as long as their intersection completely masks both of them), as required for RISC-V PTE handling.

src/arch/aarch64.rs

@@ -18,6 +18,7 @@ impl Arch for AArch64Arch {
         | Self::ENTRY_FLAG_NO_GLOBAL;
     const ENTRY_FLAG_DEFAULT_TABLE: usize
         = Self::ENTRY_FLAG_PRESENT
+        | Self::ENTRY_FLAG_READWRITE
         | 1 << 1 // Table flag
         | 1 << 10 // Access flag
         ;

src/arch/riscv64/sv39.rs

@@ -13,14 +13,11 @@ impl Arch for RiscV64Sv39Arch {
     const ENTRY_ADDRESS_WIDTH: usize = 44;
     const ENTRY_ADDRESS_SHIFT: usize = 10;
 
-    const ENTRY_FLAG_DEFAULT_PAGE: usize
-        = Self::ENTRY_FLAG_PRESENT
-        | 1 << 1 // Read flag
-        ;
+    const ENTRY_FLAG_DEFAULT_PAGE: usize = Self::ENTRY_FLAG_PRESENT | Self::ENTRY_FLAG_READONLY;
     const ENTRY_FLAG_DEFAULT_TABLE: usize = Self::ENTRY_FLAG_PRESENT;
     const ENTRY_FLAG_PRESENT: usize = 1 << 0;
-    const ENTRY_FLAG_READONLY: usize = 0;
-    const ENTRY_FLAG_READWRITE: usize = 1 << 2;
+    const ENTRY_FLAG_READONLY: usize = 1 << 1;
+    const ENTRY_FLAG_READWRITE: usize = 3 << 1;
     const ENTRY_FLAG_PAGE_USER: usize = 1 << 4;
     const ENTRY_FLAG_TABLE_USER: usize = 0;
     const ENTRY_FLAG_NO_EXEC: usize = 0;

src/arch/riscv64/sv48.rs

@@ -13,14 +13,11 @@ impl Arch for RiscV64Sv48Arch {
     const ENTRY_ADDRESS_WIDTH: usize = 44;
     const ENTRY_ADDRESS_SHIFT: usize = 10;
 
-    const ENTRY_FLAG_DEFAULT_PAGE: usize
-        = Self::ENTRY_FLAG_PRESENT
-        | 1 << 1 // Read flag
-        ;
+    const ENTRY_FLAG_DEFAULT_PAGE: usize = Self::ENTRY_FLAG_PRESENT | Self::ENTRY_FLAG_READONLY;
     const ENTRY_FLAG_DEFAULT_TABLE: usize = Self::ENTRY_FLAG_PRESENT;
     const ENTRY_FLAG_PRESENT: usize = 1 << 0;
-    const ENTRY_FLAG_READONLY: usize = 0;
-    const ENTRY_FLAG_READWRITE: usize = 1 << 2;
+    const ENTRY_FLAG_READONLY: usize = 1 << 1;
+    const ENTRY_FLAG_READWRITE: usize = 3 << 1;
     const ENTRY_FLAG_PAGE_USER: usize = 1 << 4;
     const ENTRY_FLAG_TABLE_USER: usize = 0;
     const ENTRY_FLAG_NO_EXEC: usize = 0;

src/arch/x86.rs

@@ -13,7 +13,7 @@ impl Arch for X86Arch {
 
     const ENTRY_ADDRESS_WIDTH: usize = 20;
     const ENTRY_FLAG_DEFAULT_PAGE: usize = Self::ENTRY_FLAG_PRESENT;
-    const ENTRY_FLAG_DEFAULT_TABLE: usize = Self::ENTRY_FLAG_PRESENT;
+    const ENTRY_FLAG_DEFAULT_TABLE: usize = Self::ENTRY_FLAG_PRESENT | Self::ENTRY_FLAG_READWRITE;
     const ENTRY_FLAG_PRESENT: usize = 1 << 0;
     const ENTRY_FLAG_READONLY: usize = 0;
     const ENTRY_FLAG_READWRITE: usize = 1 << 1;

src/arch/x86_64.rs

@@ -12,7 +12,7 @@ impl Arch for X8664Arch {
 
     const ENTRY_ADDRESS_WIDTH: usize = 40;
     const ENTRY_FLAG_DEFAULT_PAGE: usize = Self::ENTRY_FLAG_PRESENT;
-    const ENTRY_FLAG_DEFAULT_TABLE: usize = Self::ENTRY_FLAG_PRESENT;
+    const ENTRY_FLAG_DEFAULT_TABLE: usize = Self::ENTRY_FLAG_PRESENT | Self::ENTRY_FLAG_READWRITE;
     const ENTRY_FLAG_PRESENT: usize = 1 << 0;
     const ENTRY_FLAG_READONLY: usize = 0;
     const ENTRY_FLAG_READWRITE: usize = 1 << 1;

src/page/flags.rs

@@ -27,10 +27,7 @@ impl<A: Arch> PageFlags<A> {
         unsafe {
             Self::from_data(
                 // Flags set to present, kernel space, read-only, no-execute by default
-                A::ENTRY_FLAG_DEFAULT_TABLE
-                    | A::ENTRY_FLAG_READONLY
-                    | A::ENTRY_FLAG_NO_EXEC
-                    | A::ENTRY_FLAG_NO_GLOBAL,
+                A::ENTRY_FLAG_DEFAULT_TABLE | A::ENTRY_FLAG_NO_EXEC | A::ENTRY_FLAG_NO_GLOBAL,
             )
         }
     }
@@ -83,14 +80,19 @@ impl<A: Arch> PageFlags<A> {
     #[must_use]
     #[inline(always)]
     pub fn write(self, value: bool) -> Self {
-        // Architecture may use readonly or readwrite, support either
-        self.custom_flag(A::ENTRY_FLAG_READONLY, !value)
-            .custom_flag(A::ENTRY_FLAG_READWRITE, value)
+        // Architecture may use readonly or readwrite, or both, support either
+        if value {
+            self.custom_flag(A::ENTRY_FLAG_READONLY | A::ENTRY_FLAG_READWRITE, false)
+                .custom_flag(A::ENTRY_FLAG_READWRITE, true)
+        } else {
+            self.custom_flag(A::ENTRY_FLAG_READONLY | A::ENTRY_FLAG_READWRITE, false)
+                .custom_flag(A::ENTRY_FLAG_READONLY, true)
+        }
     }
 
     #[inline(always)]
     pub fn has_write(&self) -> bool {
-        // Architecture may use readonly or readwrite, support either
+        // Architecture may use readonly or readwrite, or both, support either
         self.data & (A::ENTRY_FLAG_READONLY | A::ENTRY_FLAG_READWRITE) == A::ENTRY_FLAG_READWRITE
     }
 

src/page/mapper.rs

@@ -120,8 +120,7 @@ impl<A: Arch, F: FrameAllocator> PageMapper<A, F> {
                     None => {
                         let next_phys = self.allocator.allocate_one()?;
                         //TODO: correct flags?
-                        let flags = A::ENTRY_FLAG_READWRITE
-                            | A::ENTRY_FLAG_DEFAULT_TABLE
+                        let flags = A::ENTRY_FLAG_DEFAULT_TABLE
                             | if virt.kind() == TableKind::User {
                                 A::ENTRY_FLAG_TABLE_USER
                             } else {