feat(kernel): kernel-owned memory model

- FrameTable: per-frame owner/use, replaces PagePool + ProcessMemory
- Quota per process, page tables charged to owner
- Regions for shared mem + device MMIO, torn down w/ owner
- Platform: create/destroy AS, map/unmap, zero_frame; drop translate_va
- RequestPages/ReleasePages/MapPage(move) checked vs kernel records
- user window 0x1000..32MiB, private pts by construction
- boot loader + device setup go through kernel api
- kernel built in place, boot allocator bounded
- isolation tests, randomized invariant test, FrameTable kani proofs
- fixes: inflated release, unmapped release, dst va unchecked,
  heap overflow, unbounded pt alloc, unzeroed frames, double free

crates/platform/Cargo.toml

@@ -5,4 +5,3 @@ edition = "2024"
 
 [dependencies]
 types = { workspace = true }
-domain = { workspace = true }

crates/platform/src/lib.rs

@@ -1,16 +1,58 @@
 #![no_std]
 
-use domain::memory::MemoryRegion;
 use types::{
     address::{EntryPoint, PhysicalAddress, StackPointer, VirtualAddress},
-    bounded::PageCount,
     id::{CoreId, IrqId, ProcessId},
-    permission::PermissionSet,
+    mapping::PagePerms,
     time::{Ticks, TimerDuration},
 };
 
+/// Supplies frames for page tables while the platform builds an address
+/// space. The kernel charges each frame to the address space's owner.
+pub trait FrameSource {
+    fn alloc_table_frame(&mut self) -> Option<PhysicalAddress>;
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum MapError {
+    /// The frame source refused to supply a page-table frame.
+    OutOfFrames,
+    /// The address is outside the user window or not page aligned.
+    InvalidAddress,
+    /// The process has no address space.
+    NoAddressSpace,
+}
+
+/// The kernel's contract with an architecture. The kernel decides what is
+/// mapped where; the platform only applies those decisions to hardware.
 pub trait Platform {
-    fn configure_protection(&mut self, process: ProcessId, regions: &[MemoryRegion]);
+    /// User mappings live in `[USER_VA_START, USER_VA_END)`. The platform
+    /// guarantees nothing else is mapped in that window in any address
+    /// space, so page tables covering it are private to each process.
+    const USER_VA_START: usize;
+    const USER_VA_END: usize;
+
+    fn create_address_space(
+        &mut self,
+        process: ProcessId,
+        frames: &mut dyn FrameSource,
+    ) -> Result<(), MapError>;
+    /// Forgets the address space. The kernel frees its frames afterwards,
+    /// so the platform must stop using them before returning.
+    fn destroy_address_space(&mut self, process: ProcessId);
+    fn map_page(
+        &mut self,
+        process: ProcessId,
+        va: VirtualAddress,
+        pa: PhysicalAddress,
+        perms: PagePerms,
+        frames: &mut dyn FrameSource,
+    ) -> Result<(), MapError>;
+    /// Removes the mapping at `va` and flushes it from the TLB.
+    fn unmap_page(&mut self, process: ProcessId, va: VirtualAddress);
+    /// Fills a frame with zeros before it is handed to a process.
+    fn zero_frame(&mut self, pa: PhysicalAddress);
+
     fn enable_user_mode(&mut self, entry: EntryPoint, stack: StackPointer) -> !;
     fn set_timer(&mut self, duration: TimerDuration);
     fn current_ticks(&self) -> Ticks;
@@ -19,22 +61,6 @@ pub trait Platform {
     fn send_ipi(&mut self, target: CoreId);
     fn core_id(&self) -> CoreId;
     fn num_cores(&self) -> u8;
-    fn map_shared(
-        &mut self,
-        process: ProcessId,
-        base: PhysicalAddress,
-        size: PageCount,
-        permissions: PermissionSet,
-    );
     fn halt(&self) -> !;
     fn debug_putchar(&self, byte: u8);
-    fn translate_va(&self, process: ProcessId, va: VirtualAddress) -> Option<PhysicalAddress>;
-    fn map_user_page(
-        &mut self,
-        process: ProcessId,
-        va: VirtualAddress,
-        pa: PhysicalAddress,
-        writable: bool,
-        executable: bool,
-    );
 }