riscv: impl pmp

artiq/firmware/libboard_misoc/riscv32ima/boot.rs

@@ -1,4 +1,5 @@
-use super::cache;
+use super::{cache, pmp};
+use riscv::register::*;
 
 pub unsafe fn reset() -> ! {
     llvm_asm!(r#"
@@ -16,3 +17,14 @@ pub unsafe fn jump(addr: usize) -> ! {
     "# : : "r"(addr) : : "volatile");
     loop {}
 }
+
+pub unsafe fn start_user(addr: usize) -> ! {
+    pmp::enable_user_memory();
+    mstatus::set_mpp(mstatus::MPP::User);
+    mepc::write(addr);
+    llvm_asm!(
+        "mret"
+        : : : : "volatile"
+    );
+    unreachable!()
+}

artiq/firmware/libboard_misoc/riscv32ima/mod.rs

@@ -1,2 +1,3 @@
 pub mod cache;
 pub mod boot;
+pub mod pmp;

artiq/firmware/libboard_misoc/riscv32ima/pmp.rs

@@ -0,0 +1,55 @@
+use riscv::register::{pmpaddr0, pmpaddr1, pmpaddr2, pmpaddr3, pmpcfg0};
+
+static mut THREAD_DEPTH: u8 = 0;
+
+const PMP_L    : usize = 0b10000000;
+const PMP_NAPOT: usize = 0b00011000;
+const PMP_X    : usize = 0b00000100;
+const PMP_W    : usize = 0b00000010;
+const PMP_R    : usize = 0b00000001;
+const PMP_OFF  : usize = 0b00000000;
+
+#[inline(always)]
+pub unsafe fn init_stack_guard(guard_base: usize) {
+    pmpaddr2::write((guard_base >> 2) | ((0x1000 - 1) >> 3));
+    pmpcfg0::write((PMP_L | PMP_NAPOT) << 16);
+}
+
+#[inline(always)]
+pub fn enable_user_memory() {
+    pmpaddr3::write((0x80000000 - 1) >> 3);
+    pmpcfg0::write((PMP_L | PMP_NAPOT | PMP_X | PMP_W | PMP_R) << 24);
+}
+
+#[inline(always)]
+pub unsafe fn push_pmp_region(addr: usize) {
+    let pmp_addr = (addr >> 2) | ((0x1000 - 1) >> 3);
+    match THREAD_DEPTH {
+        // Activate PMP0 when switching from main stack to thread
+        0 => {
+            pmpaddr0::write(pmp_addr);
+            pmpcfg0::write(PMP_NAPOT);
+        }
+
+        // Temporarily activate PMP1 when spawning a thread from a thread
+        // The thread should swap back to the main stack very soon after init
+        1 => {
+            pmpaddr1::write(pmp_addr);
+            pmpcfg0::write(PMP_NAPOT << 8 | PMP_NAPOT);
+        }
+
+        // Thread *running* another thread should not be possible
+        _ => unreachable!()
+    }
+    THREAD_DEPTH += 1;
+}
+
+#[inline(always)]
+pub unsafe fn pop_pmp_region() {
+    THREAD_DEPTH -= 1;
+    match THREAD_DEPTH {
+        0 => pmpcfg0::write(PMP_OFF),
+        1 => pmpcfg0::write(PMP_NAPOT),
+        _ => unreachable!()
+    }
+}