rustubs/arch/x86_64/

interrupt.rs

mod idt;
pub mod pic_8259;
pub mod pit;
pub mod plugbox;
use crate::arch::x86_64::arch_regs::TrapFrame;
use crate::arch::x86_64::gdt;
use crate::arch::x86_64::is_int_enabled;
use crate::arch::x86_64::paging::fault;
use crate::arch::x86_64::RFLAGS_IF_MASK;
use crate::defs::IntNumber as INT;
use crate::io::*;
use crate::machine::interrupt::plugbox::IRQ_GATE_MAP;
use crate::proc::sched::Scheduler;
use crate::proc::sync::*;
use core::arch::asm;

#[no_mangle]
#[cfg(target_arch = "x86_64")]
extern "C" fn trap_gate(nr: u16, fp: u64) {
	// cpu automatically masks interrupts so we are already in L3
	if nr < 0x20 {
		handle_exception(nr, fp);
	} else if nr == INT::SYSCALL {
		handle_syscall(fp);
	} else {
		unsafe { handle_irq(nr) };
	}

	// yield CPU if this process has been marked as killed
	use crate::proc::task::{Task, TaskState};
	let t = match Task::current() {
		Some(t) => t,
		None => {
			interrupt_enable();
			return;
		}
	};

	// TODO mark the true branch as "unlikely"
	// TODO this could be buggy. Are we sure L2 must be free here?
	if t.state == TaskState::Dead {
		interrupt_enable();
		Scheduler::yield_cpu();
	} else {
		// a context swap may have happened in the kernel mode.
		// if the original interrupt (exception) was from user space, we need to
		// restore the correct kernel stack pointer in the tss.rsp0;
		// tss.rsp0 doesn't matter as long as we stay in kernel mode.
		let tf = unsafe { &*(fp as *const TrapFrame) };
		if tf.from_user() {
			unsafe {
				gdt::set_tss_ksp(t.get_init_kernel_sp());
			}
		}
		interrupt_enable();
	}
}

#[inline]
/// handle_irq assumes the interrupt is **disabled** when called.
/// this will also make sure interrupt is disabled when it returns
unsafe fn handle_irq(nr: u16) {
	let irq_gate = match IRQ_GATE_MAP.get(&nr) {
		None => {
			panic!("no handler for irq {}", nr);
		}
		Some(g) => g,
	};
	// execute the prologue
	irq_gate.call_prologue();
	let epi = irq_gate.get_epilogue();
	if epi.is_none() {
		// TODO? we could also take a look into the epilogue queue here when the
		// current irq doesn't have an epilogue itself. But optimistically, if
		// the epilogue queue is not empty, it's very likely someone else is
		// already working on it, so we just leave for now....
		return;
	}
	let epi = epi.unwrap();
	if !IS_L2_AVAILABLE() {
		EPILOGUE_QUEUE.l3_get_ref_mut().queue.push_back(epi);
		return;
	}
	// L2 is available, we run the epilogue now, also clear the queue before
	// return
	ENTER_L2();
	interrupt_enable();
	unsafe {
		epi.call();
	}
	// we need to clear the epilogue queue on behalf of others. Modifying the
	// epilogue is a level 3 critical section
	let mut epi: Option<EpilogueEntrant>;
	let mut done;
	loop {
		let r = irq_save();
		let rq = EPILOGUE_QUEUE.l3_get_ref_mut();
		epi = rq.queue.pop_front();
		done = rq.queue.is_empty();
		irq_restore(r);

		if let Some(e) = epi {
			debug_assert!(is_int_enabled());
			e.call();
		}
		// This is a linearization point where we may do rescheduling. Unlike
		// OOStuBS, we don't do rescheduling in the device epilogues. this
		// decouples the scheduler from the timer interrupt driver, also has
		// better "real-time" guarantee: rescheduling will not be delayed by
		// more than one epilogue execution; OOStuBS doesn't have the delay
		// issue because every epilogue is enqueued at most once due to the
		// limitation of having no memory management.
		//
		// this also means that ALL rescheduling must be done in the level 2.
		// otherwise 1) rescheduling may not be strictly linearized, if the CPU
		// is not running fast enough there might be issues caused by spurious
		// (timer) interrupts. 2) even if you can guarantee linearization, there
		// is still a dead lock situation that, if the try_reschedule /
		// do_reschedule was called the at a wrong place, the execution may not
		// release the L2 lock when they are scheduled back. 3) this also
		// requires you do explicitly release L2 lock on new task entrance (when
		// they are scheduled for the first time). I'm not a big fan of this but
		// there is nothing much I can do right now.
		Scheduler::try_reschedule();
		if done {
			break;
		}
	}
	// you need to make sure the interrupt is disabled at this point
	LEAVE_L2();
}

/// handles exception/faults (nr < 32);
#[inline]
fn handle_exception(nr: u16, fp: u64) {
	let frame = unsafe { &mut *(fp as *mut TrapFrame) };
	match nr {
		INT::PAGEFAULT => {
			let fault_address = fault::get_fault_addr();
			fault::page_fault_handler(frame, fault_address)
		}
		_ => {
			sprint!("[trap {}] {:#X?}", nr, frame);
			unsafe { asm!("hlt") };
		}
	}
}

/// dispatch a syscall (int 0x80). The syscall number is in rax; args in
/// rdi, rsi, rdx. The return value is written back into the trap frame's rax
/// so iretq returns it to user space.
#[inline]
fn handle_syscall(fp: u64) {
	let frame = unsafe { &mut *(fp as *mut TrapFrame) };
	let nr = frame.rax;
	let a0 = frame.rdi;
	let a1 = frame.rsi;
	let a2 = frame.rdx;
	// syscalls are voluntary traps, not hardware IRQs. Enable interrupts so
	// that sys_exit -> yield_cpu and sys_write (which may block on the console
	// lock) work correctly.
	interrupt_enable();
	let ret = crate::syscalls::dispatch(fp, nr, a0, a1, a2);
	frame.rax = ret;
}

#[inline(always)]
pub fn interrupt_enable() { unsafe { asm!("sti") }; }

#[inline(always)]
pub fn interrupt_disable() { unsafe { asm!("cli") }; }

#[inline]
/// irq_save() disables all interrupts and returns the previous state
pub fn irq_save() -> bool {
	let rflags: u64;
	unsafe {
		asm!(
			"pushfq",
			"cli",
			"pop {}",
			out(reg) rflags,
		)
	};
	(rflags & RFLAGS_IF_MASK) != 0
}

#[inline]
/// irq_restore only re-enable irq if was_enabled==true. it will not disable irq
/// regardless the was_enabled value. This function should only be called to
/// restore irq based on previous irq_save();
pub fn irq_restore(was_enabled: bool) {
	if was_enabled {
		interrupt_enable();
	}
}

/// initialize the idt and [pic_8259]
pub fn init() {
	idt::init();
	pic_8259::init();
}