0.3.0: converge kernel onto upstream master

- Rebase all Red Bear kernel changes onto upstream master (4d5d36d4).
- Update version to 0.5.12+rb0.3.0 and add Red Bear author attribution.
- Switch redox_syscall direct dependency to local fork path (../syscall).
- Bump rust-toolchain.toml to nightly-2026-05-24.
- Regenerate Cargo.lock for +rb0.3.0 suffixes and path deps.

src/percpu.rs

@@ -12,14 +12,11 @@ use syscall::PtraceFlags;
 
 use crate::{
     arch::device::ArchPercpuMisc,
-    context::{
-        empty_cr3,
-        memory::{AddrSpaceSwitchReadGuard, AddrSpaceWrapper},
-        switch::ContextSwitchPercpu,
-    },
+    context::{empty_cr3, memory::AddrSpaceWrapper, switch::ContextSwitchPercpu},
     cpu_set::{LogicalCpuId, MAX_CPU_COUNT},
     cpu_stats::{CpuStats, CpuStatsData},
     ptrace::Session,
+    sync::CleanLockToken,
     syscall::debug::SyscallDebugInfo,
 };
 
@@ -33,8 +30,9 @@ pub struct PercpuBlock {
 
     pub current_addrsp: RefCell<Option<Arc<AddrSpaceWrapper>>>,
     pub new_addrsp_tmp: Cell<Option<Arc<AddrSpaceWrapper>>>,
-    pub new_addrsp_guard: Cell<Option<AddrSpaceSwitchReadGuard>>,
     pub wants_tlb_shootdown: AtomicBool,
+    pub balance: Cell<[usize; 40]>,
+    pub last_queue: Cell<usize>,
 
     // TODO: Put mailbox queues here, e.g. for TLB shootdown? Just be sure to 128-byte align it
     // first to avoid cache invalidation.
@@ -134,7 +132,6 @@ pub unsafe fn switch_arch_hook() {
 
         let cur_addrsp = percpu.current_addrsp.borrow();
         let next_addrsp = percpu.new_addrsp_tmp.take();
-        let next_addrsp_guard = percpu.new_addrsp_guard.take();
 
         let retain_pgtbl = match (&*cur_addrsp, &next_addrsp) {
             (Some(p), Some(n)) => Arc::ptr_eq(p, n),
@@ -167,13 +164,14 @@ pub unsafe fn switch_arch_hook() {
         // space.
         *percpu.current_addrsp.borrow_mut() = next_addrsp;
 
-        if let Some(next_addrsp) = &*percpu.current_addrsp.borrow() {
-            next_addrsp.used_by.atomic_set(percpu.cpu_id);
-        }
-        match next_addrsp_guard {
+        match &*percpu.current_addrsp.borrow() {
             Some(next_addrsp) => {
-                next_addrsp.table.utable.make_current();
-                drop(next_addrsp);
+                next_addrsp.used_by.atomic_set(percpu.cpu_id);
+                let mut token = CleanLockToken::new();
+                let mut token = token.token();
+                let next = next_addrsp.acquire_read(token.downgrade());
+
+                next.table.utable.make_current();
             }
             _ => {
                 crate::memory::RmmA::set_table(rmm::TableKind::User, empty_cr3());
@@ -188,8 +186,9 @@ impl PercpuBlock {
             switch_internals: ContextSwitchPercpu::default(),
             current_addrsp: RefCell::new(None),
             new_addrsp_tmp: Cell::new(None),
-            new_addrsp_guard: Cell::new(None),
             wants_tlb_shootdown: AtomicBool::new(false),
+            balance: Cell::new([0; 40]),
+            last_queue: Cell::new(39),
             ptrace_flags: Cell::new(PtraceFlags::empty()),
             ptrace_session: RefCell::new(None),
             inside_syscall: Cell::new(false),