[hal] Support user space for riscv64 and aarch64

modules/axhal/src/arch/aarch64/context.rs

@@ -15,6 +15,145 @@ pub struct TrapFrame {
     pub spsr: u64,
 }
 
+impl TrapFrame {
+    /// Gets the 0th syscall argument.
+    pub const fn arg0(&self) -> usize {
+        self.r[0] as _
+    }
+
+    /// Gets the 1st syscall argument.
+    pub const fn arg1(&self) -> usize {
+        self.r[1] as _
+    }
+
+    /// Gets the 2nd syscall argument.
+    pub const fn arg2(&self) -> usize {
+        self.r[2] as _
+    }
+
+    /// Gets the 3rd syscall argument.
+    pub const fn arg3(&self) -> usize {
+        self.r[3] as _
+    }
+
+    /// Gets the 4th syscall argument.
+    pub const fn arg4(&self) -> usize {
+        self.r[4] as _
+    }
+
+    /// Gets the 5th syscall argument.
+    pub const fn arg5(&self) -> usize {
+        self.r[5] as _
+    }
+}
+
+/// Context to enter user space.
+#[cfg(feature = "uspace")]
+pub struct UspaceContext(TrapFrame);
+
+#[cfg(feature = "uspace")]
+impl UspaceContext {
+    /// Creates an empty context with all registers set to zero.
+    pub const fn empty() -> Self {
+        unsafe { core::mem::MaybeUninit::zeroed().assume_init() }
+    }
+
+    /// Creates a new context with the given entry point, user stack pointer,
+    /// and the argument.
+    pub fn new(entry: usize, ustack_top: VirtAddr, arg0: usize) -> Self {
+        use aarch64_cpu::registers::SPSR_EL1;
+        let mut regs = [0; 31];
+        regs[0] = arg0 as _;
+        Self(TrapFrame {
+            r: regs,
+            usp: ustack_top.as_usize() as _,
+            elr: entry as _,
+            spsr: (SPSR_EL1::M::EL0t
+                + SPSR_EL1::D::Masked
+                + SPSR_EL1::A::Masked
+                + SPSR_EL1::I::Unmasked
+                + SPSR_EL1::F::Masked)
+                .value,
+        })
+    }
+
+    /// Creates a new context from the given [`TrapFrame`].
+    pub const fn from(trap_frame: &TrapFrame) -> Self {
+        Self(*trap_frame)
+    }
+
+    /// Gets the instruction pointer.
+    pub const fn get_ip(&self) -> usize {
+        self.0.elr as _
+    }
+
+    /// Gets the stack pointer.
+    pub const fn get_sp(&self) -> usize {
+        self.0.usp as _
+    }
+
+    /// Sets the instruction pointer.
+    pub const fn set_ip(&mut self, pc: usize) {
+        self.0.elr = pc as _;
+    }
+
+    /// Sets the stack pointer.
+    pub const fn set_sp(&mut self, sp: usize) {
+        self.0.usp = sp as _;
+    }
+
+    /// Sets the return value register.
+    pub const fn set_retval(&mut self, retval: usize) {
+        self.0.r[8] = retval as _;
+    }
+
+    /// Enters user space.
+    ///
+    /// It restores the user registers and jumps to the user entry point
+    /// (saved in `sepc`).
+    /// When an exception or syscall occurs, the kernel stack pointer is
+    /// switched to `kstack_top`.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because it changes processor mode and the stack.
+    #[inline(never)]
+    #[no_mangle]
+    pub unsafe fn enter_uspace(&self, kstack_top: VirtAddr) -> ! {
+        super::disable_irqs();
+        // We don't process elxt trap, so we don't need to save the current kstack ptr to the taskctx.
+        asm!(
+            "
+            mov     sp, x1
+            ldp     x30, x9, [x0, 30 * 8]
+            ldp     x10, x11, [x0, 32 * 8]
+            msr     sp_el0, x9
+            msr     elr_el1, x10
+            msr     spsr_el1, x11
+
+            ldp     x28, x29, [x0, 28 * 8]
+            ldp     x26, x27, [x0, 26 * 8]
+            ldp     x24, x25, [x0, 24 * 8]
+            ldp     x22, x23, [x0, 22 * 8]
+            ldp     x20, x21, [x0, 20 * 8]
+            ldp     x18, x19, [x0, 18 * 8]
+            ldp     x16, x17, [x0, 16 * 8]
+            ldp     x14, x15, [x0, 14 * 8]
+            ldp     x12, x13, [x0, 12 * 8]
+            ldp     x10, x11, [x0, 10 * 8]
+            ldp     x8, x9, [x0, 8 * 8]
+            ldp     x6, x7, [x0, 6 * 8]
+            ldp     x4, x5, [x0, 4 * 8]
+            ldp     x2, x3, [x0, 2 * 8]
+            ldp     x0, x1, [x0]
+            eret",
+            in("x0") &self.0,
+            in("x1") kstack_top.as_usize() ,
+            options(noreturn),
+        )
+    }
+}
+
 /// FP & SIMD registers.
 #[repr(C, align(16))]
 #[derive(Debug, Default)]
@@ -47,7 +186,7 @@ impl FpState {
 /// and the next task restores its context from memory to CPU.
 #[allow(missing_docs)]
 #[repr(C)]
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub struct TaskContext {
     pub sp: u64,
     pub tpidr_el0: u64,
@@ -65,6 +204,9 @@ pub struct TaskContext {
     pub lr: u64, // r30
     #[cfg(feature = "fp_simd")]
     pub fp_state: FpState,
+    /// The `ttbr0_el1` register value, i.e., the page table root.
+    #[cfg(feature = "uspace")]
+    pub ttbr0_el1: memory_addr::PhysAddr,
 }
 
 impl TaskContext {
@@ -75,25 +217,48 @@ impl TaskContext {
     ///
     /// [`init`]: TaskContext::init
     /// [`switch_to`]: TaskContext::switch_to
-    pub const fn new() -> Self {
-        unsafe { core::mem::MaybeUninit::zeroed().assume_init() }
+    pub fn new() -> Self {
+        Self {
+            #[cfg(feature = "uspace")]
+            ttbr0_el1: crate::paging::kernel_page_table_root(),
+            ..Default::default()
+        }
     }
 
     /// Initializes the context for a new task, with the given entry point and
     /// kernel stack.
     pub fn init(&mut self, entry: usize, kstack_top: VirtAddr, tls_area: VirtAddr) {
         self.sp = kstack_top.as_usize() as u64;
         self.lr = entry as u64;
+        // When under `uspace` feature, kernel will not use this register.
         self.tpidr_el0 = tls_area.as_usize() as u64;
     }
 
+    /// Changes the page table root for user space (`ttbr0_el1` register for aarch64 in el1 level).
+    ///
+    /// If not set, the kernel page table root is used (obtained by
+    /// [`axhal::paging::kernel_page_table_root`][1]).
+    ///
+    /// [1]: crate::paging::kernel_page_table_root
+    #[cfg(feature = "uspace")]
+    pub fn set_page_table_root(&mut self, ttbr0_el1: memory_addr::PhysAddr) {
+        self.ttbr0_el1 = ttbr0_el1;
+    }
+
     /// Switches to another task.
     ///
     /// It first saves the current task's context from CPU to this place, and then
     /// restores the next task's context from `next_ctx` to CPU.
     pub fn switch_to(&mut self, next_ctx: &Self) {
         #[cfg(feature = "fp_simd")]
         self.fp_state.switch_to(&next_ctx.fp_state);
+
+        #[cfg(feature = "uspace")]
+        {
+            if self.ttbr0_el1 != next_ctx.ttbr0_el1 {
+                unsafe { super::write_page_table_root0(next_ctx.ttbr0_el1) };
+            }
+        }
         unsafe { context_switch(self, next_ctx) }
     }
 }

modules/axhal/src/arch/aarch64/mod.rs

@@ -4,6 +4,8 @@ pub(crate) mod trap;
 use core::arch::asm;
 
 use aarch64_cpu::registers::{DAIF, TPIDR_EL0, TTBR0_EL1, TTBR1_EL1, VBAR_EL1};
+#[cfg(feature = "uspace")]
+pub use context::UspaceContext;
 use memory_addr::{PhysAddr, VirtAddr};
 use tock_registers::interfaces::{Readable, Writeable};
 

modules/axhal/src/arch/aarch64/trap.S

@@ -21,6 +21,13 @@
     mrs     x11, spsr_el1
     stp     x30, x9, [sp, 30 * 8]
     stp     x10, x11, [sp, 32 * 8]
+    /*
+    * We may have interrupted userspace, or a guest, or exit-from or 
+    * return-to either of those. So we can't trust sp_el0, and need to
+    * restore it.
+     */
+    bl      current_task_ptr_raw
+    msr     sp_el0, x0
 .endm
 
 .macro RESTORE_REGS

modules/axhal/src/arch/aarch64/trap.rs

@@ -98,8 +98,9 @@ fn handle_sync_exception(tf: &mut TrapFrame) {
     let esr = ESR_EL1.extract();
     let iss = esr.read(ESR_EL1::ISS);
     match esr.read_as_enum(ESR_EL1::EC) {
+        #[cfg(feature = "uspace")]
         Some(ESR_EL1::EC::Value::SVC64) => {
-            warn!("No syscall is supported currently!");
+            tf.r[0] = crate::trap::handle_syscall(tf, tf.r[8] as usize) as u64;
         }
         Some(ESR_EL1::EC::Value::InstrAbortLowerEL) => handle_instruction_abort(tf, iss, true),
         Some(ESR_EL1::EC::Value::InstrAbortCurrentEL) => handle_instruction_abort(tf, iss, false),