path: root/devices/src/ioapic.rs

// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Implementation of an intel 82093AA Input/Output Advanced Programmable Interrupt Controller
// See https://pdos.csail.mit.edu/6.828/2016/readings/ia32/ioapic.pdf for a specification.

use crate::split_irqchip_common::*;
use crate::BusDevice;
use bit_field::*;
use kvm::Vm;
use msg_socket::{MsgReceiver, MsgSender};
use std::sync::Arc;
use sys_util::{error, warn, EventFd, Result};
use vm_control::{VmIrqRequest, VmIrqRequestSocket, VmIrqResponse};

#[bitfield]
#[derive(Clone, Copy, PartialEq)]
pub struct RedirectionTableEntry {
    vector: BitField8,
    #[bits = 3]
    delivery_mode: DeliveryMode,
    #[bits = 1]
    dest_mode: DestinationMode,
    #[bits = 1]
    delivery_status: DeliveryStatus,
    polarity: BitField1,
    remote_irr: bool,
    #[bits = 1]
    trigger_mode: TriggerMode,
    interrupt_mask: bool, // true iff interrupts are masked.
    reserved: BitField39,
    dest_id: BitField8,
}

#[bitfield]
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum DeliveryStatus {
    Idle = 0,
    Pending = 1,
}

const IOAPIC_VERSION_ID: u32 = 0x00170011;
pub const IOAPIC_BASE_ADDRESS: u64 = 0xfec00000;
// The Intel manual does not specify this size, but KVM uses it.
pub const IOAPIC_MEM_LENGTH_BYTES: u64 = 0x100;

// Constants for IOAPIC direct register offset.
const IOAPIC_REG_ID: u8 = 0x00;
const IOAPIC_REG_VERSION: u8 = 0x01;
const IOAPIC_REG_ARBITRATION_ID: u8 = 0x02;

// Register offsets
const IOREGSEL_OFF: u8 = 0x0;
const IOREGSEL_DUMMY_UPPER_32_BITS_OFF: u8 = 0x4;
const IOWIN_OFF: u8 = 0x10;
const IOWIN_SCALE: u8 = 0x2;

/// Given an IRQ and whether or not the selector should refer to the high bits, return a selector
/// suitable to use as an offset to read to/write from.
#[allow(dead_code)]
fn encode_selector_from_irq(irq: usize, is_high_bits: bool) -> u8 {
    (irq as u8) * IOWIN_SCALE + IOWIN_OFF + (is_high_bits as u8)
}

/// Given an offset that was read from/written to, return a tuple of the relevant IRQ and whether
/// the offset refers to the high bits of that register.
fn decode_irq_from_selector(selector: u8) -> (usize, bool) {
    (
        ((selector - IOWIN_OFF) / IOWIN_SCALE) as usize,
        selector & 1 != 0,
    )
}

// The RTC needs special treatment to work properly for Windows (or other OSs that use tick
// stuffing). In order to avoid time drift, we need to guarantee that the correct number of RTC
// interrupts are injected into the guest. This hack essentialy treats RTC interrupts as level
// triggered, which allows the IOAPIC to be responsible for interrupt coalescing and allows the
// IOAPIC to pass back whether or not the interrupt was coalesced to the CMOS (which allows the
// CMOS to perform tick stuffing). This deviates from the IOAPIC spec in ways very similar to (but
// not exactly the same as) KVM's IOAPIC.
const RTC_IRQ: usize = 0x8;

pub struct Ioapic {
    id: u32,
    // Remote IRR for Edge Triggered Real Time Clock interrupts, which allows the CMOS to know when
    // one of its interrupts is being coalesced.
    rtc_remote_irr: bool,
    current_interrupt_level_bitmap: u32,
    redirect_table: [RedirectionTableEntry; kvm::NUM_IOAPIC_PINS],
    // IOREGSEL is technically 32 bits, but only bottom 8 are writable: all others are fixed to 0.
    ioregsel: u8,
    relay: Arc<GsiRelay>,
    irqfd: Vec<EventFd>,
    socket: VmIrqRequestSocket,
}

impl BusDevice for Ioapic {
    fn debug_label(&self) -> String {
        "userspace IOAPIC".to_string()
    }

    fn read(&mut self, offset: u64, data: &mut [u8]) {
        if data.len() > 8 || data.len() == 0 {
            warn!("IOAPIC: Bad read size: {}", data.len());
            return;
        }
        if offset >= 1 << 8 {
            warn!("IOAPIC: Bad read from offset {}", offset);
        }
        let out = match offset as u8 {
            IOREGSEL_OFF => self.ioregsel.into(),
            IOREGSEL_DUMMY_UPPER_32_BITS_OFF => 0,
            IOWIN_OFF => self.ioapic_read(),
            _ => {
                warn!("IOAPIC: Bad read from offset {}", offset);
                return;
            }
        };
        let out_arr = out.to_ne_bytes();
        for i in 0..4 {
            if i < data.len() {
                data[i] = out_arr[i];
            }
        }
    }

    fn write(&mut self, offset: u64, data: &[u8]) {
        if data.len() > 8 || data.len() == 0 {
            warn!("IOAPIC: Bad write size: {}", data.len());
            return;
        }
        if offset >= 1 << 8 {
            warn!("IOAPIC: Bad write to offset {}", offset);
        }
        match offset as u8 {
            IOREGSEL_OFF => self.ioregsel = data[0],
            IOREGSEL_DUMMY_UPPER_32_BITS_OFF => {} // Ignored.
            IOWIN_OFF => {
                if data.len() != 4 {
                    warn!("IOAPIC: Bad write size for iowin: {}", data.len());
                    return;
                }
                let data_arr = [data[0], data[1], data[2], data[3]];
                let val = u32::from_ne_bytes(data_arr);
                self.ioapic_write(val);
            }
            _ => {
                warn!("IOAPIC: Bad write to offset {}", offset);
            }
        }
    }
}

impl Ioapic {
    pub fn new(vm: &mut Vm, socket: VmIrqRequestSocket) -> Result<Ioapic> {
        let mut entry = RedirectionTableEntry::new();
        entry.set_interrupt_mask(true);
        let entries = [entry; kvm::NUM_IOAPIC_PINS];
        let mut irqfd = vec![];
        for i in 0..kvm::NUM_IOAPIC_PINS {
            irqfd.push(EventFd::new()?);
            vm.register_irqfd(&irqfd[i], i as u32)?;
        }
        Ok(Ioapic {
            id: 0,
            rtc_remote_irr: false,
            current_interrupt_level_bitmap: 0,
            redirect_table: entries,
            ioregsel: 0,
            relay: Default::default(),
            irqfd,
            socket,
        })
    }

    pub fn register_relay(&mut self, relay: Arc<GsiRelay>) {
        self.relay = relay;
    }

    // The ioapic must be informed about EOIs in order to avoid sending multiple interrupts of the
    // same type at the same time.
    pub fn end_of_interrupt(&mut self, vector: u8) {
        if self.redirect_table[RTC_IRQ].get_vector() == vector && self.rtc_remote_irr {
            // Specifically clear RTC IRQ field
            self.rtc_remote_irr = false;
        }

        for i in 0..kvm::NUM_IOAPIC_PINS {
            if self.redirect_table[i].get_vector() == vector
                && self.redirect_table[i].get_trigger_mode() == TriggerMode::Level
            {
                if self.relay.irqfd_resample[i].is_some() {
                    self.service_irq(i, false);
                }
                if let Some(resample_evt) = &self.relay.irqfd_resample[i] {
                    resample_evt.write(1).unwrap();
                }
                self.redirect_table[i].set_remote_irr(false);
            }
            // There is an inherent race condition in hardware if the OS is finished processing an
            // interrupt and a new interrupt is delivered between issuing an EOI and the EOI being
            // completed.  When that happens the ioapic is supposed to re-inject the interrupt.
            if self.current_interrupt_level_bitmap & (1 << i) != 0 {
                self.service_irq(i, true);
            }
        }
    }

    pub fn service_irq(&mut self, irq: usize, level: bool) -> bool {
        let entry = &mut self.redirect_table[irq];

        // De-assert the interrupt.
        if !level {
            self.current_interrupt_level_bitmap &= !(1 << irq);
            return true;
        }

        // If it's an edge-triggered interrupt that's already high we ignore it.
        if entry.get_trigger_mode() == TriggerMode::Edge
            && self.current_interrupt_level_bitmap & (1 << irq) != 0
        {
            return false;
        }

        self.current_interrupt_level_bitmap |= 1 << irq;

        // Interrupts are masked, so don't inject.
        if entry.get_interrupt_mask() {
            return false;
        }

        // Level-triggered and remote irr is already active, so we don't inject a new interrupt.
        // (Coalesce with the prior one(s)).
        if entry.get_trigger_mode() == TriggerMode::Level && entry.get_remote_irr() {
            return false;
        }

        // Coalesce RTC interrupt to make tick stuffing work.
        if irq == RTC_IRQ && self.rtc_remote_irr {
            return false;
        }

        let injected = self.irqfd[irq].write(1).is_ok();

        if entry.get_trigger_mode() == TriggerMode::Level && level && injected {
            entry.set_remote_irr(true);
        } else if irq == RTC_IRQ && injected {
            self.rtc_remote_irr = true;
        }

        injected
    }

    fn ioapic_write(&mut self, val: u32) {
        match self.ioregsel {
            IOAPIC_REG_VERSION => { /* read-only register */ }
            IOAPIC_REG_ID => self.id = (val >> 24) & 0xf,
            IOAPIC_REG_ARBITRATION_ID => { /* read-only register */ }
            _ => {
                if self.ioregsel < IOWIN_OFF {
                    // Invalid write; ignore.
                    return;
                }
                let (index, is_high_bits) = decode_irq_from_selector(self.ioregsel);
                if index >= kvm::NUM_IOAPIC_PINS {
                    // Invalid write; ignore.
                    return;
                }

                let entry = &mut self.redirect_table[index];
                if is_high_bits {
                    entry.set(32, 32, val.into());
                } else {
                    let before = *entry;
                    entry.set(0, 32, val.into());

                    // respect R/O bits.
                    entry.set_delivery_status(before.get_delivery_status());
                    entry.set_remote_irr(before.get_remote_irr());

                    // Clear remote_irr when switching to edge_triggered.
                    if entry.get_trigger_mode() == TriggerMode::Edge {
                        entry.set_remote_irr(false);
                    }

                    // NOTE: on pre-4.0 kernels, there's a race we would need to work around.
                    // "KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race"
                    // is the fix for this.
                }

                if self.redirect_table[index].get_trigger_mode() == TriggerMode::Level
                    && self.current_interrupt_level_bitmap & (1 << index) != 0
                    && !self.redirect_table[index].get_interrupt_mask()
                {
                    self.service_irq(index, true);
                }

                let mut address = MsiAddressMessage::new();
                let mut data = MsiDataMessage::new();
                let entry = &self.redirect_table[index];
                address.set_destination_mode(entry.get_dest_mode());
                address.set_destination_id(entry.get_dest_id());
                address.set_always_0xfee(0xfee);
                data.set_vector(entry.get_vector());
                data.set_delivery_mode(entry.get_delivery_mode());
                data.set_trigger(entry.get_trigger_mode());

                let request = VmIrqRequest::AddMsiRoute {
                    gsi: index as u32,
                    msi_address: address.get(0, 32),
                    msi_data: data.get(0, 32) as u32,
                };
                if let Err(e) = self.socket.send(&request) {
                    error!("IOAPIC: failed to send AddMsiRoute request: {}", e);
                    return;
                }
                match self.socket.recv() {
                    Ok(response) => {
                        if let VmIrqResponse::Err(e) = response {
                            error!("IOAPIC: failed to add msi route: {}", e);
                        }
                    }
                    Err(e) => {
                        error!("IOAPIC: failed to receive AddMsiRoute response: {}", e);
                    }
                }
            }
        }
    }

    fn ioapic_read(&mut self) -> u32 {
        match self.ioregsel {
            IOAPIC_REG_VERSION => IOAPIC_VERSION_ID,
            IOAPIC_REG_ID | IOAPIC_REG_ARBITRATION_ID => (self.id & 0xf) << 24,
            _ => {
                if self.ioregsel < IOWIN_OFF {
                    // Invalid read; ignore and return 0.
                    0
                } else {
                    let (index, is_high_bits) = decode_irq_from_selector(self.ioregsel);
                    if index < kvm::NUM_IOAPIC_PINS {
                        let offset = if is_high_bits { 32 } else { 0 };
                        self.redirect_table[index].get(offset, 32) as u32
                    } else {
                        !0 // Invaild index - return all 1s
                    }
                }
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    const DEFAULT_VECTOR: u8 = 0x3a;
    const DEFAULT_DESTINATION_ID: u8 = 0x5f;

    fn new() -> Ioapic {
        let kvm = kvm::Kvm::new().unwrap();
        let gm = sys_util::GuestMemory::new(&vec![(sys_util::GuestAddress(0), 0x1000)]).unwrap();
        let mut vm = Vm::new(&kvm, gm).unwrap();
        vm.enable_split_irqchip().unwrap();
        let (_, device_socket) = msg_socket::pair::<VmIrqResponse, VmIrqRequest>().unwrap();
        Ioapic::new(&mut vm, device_socket).unwrap()
    }

    fn set_up(trigger: TriggerMode) -> (Ioapic, usize) {
        let irq = kvm::NUM_IOAPIC_PINS - 1;
        let ioapic = set_up_with_irq(irq, trigger);
        (ioapic, irq)
    }

    fn set_up_with_irq(irq: usize, trigger: TriggerMode) -> Ioapic {
        let mut ioapic = self::new();
        set_up_redirection_table_entry(&mut ioapic, irq, trigger);
        ioapic
    }

    fn read_reg(ioapic: &mut Ioapic, selector: u8) -> u32 {
        let mut data = [0; 4];
        ioapic.write(IOREGSEL_OFF.into(), &[selector]);
        ioapic.read(IOWIN_OFF.into(), &mut data);
        u32::from_ne_bytes(data)
    }

    fn write_reg(ioapic: &mut Ioapic, selector: u8, value: u32) {
        ioapic.write(IOREGSEL_OFF.into(), &[selector]);
        ioapic.write(IOWIN_OFF.into(), &value.to_ne_bytes());
    }

    fn read_entry(ioapic: &mut Ioapic, irq: usize) -> RedirectionTableEntry {
        let mut entry = RedirectionTableEntry::new();
        entry.set(
            0,
            32,
            read_reg(ioapic, encode_selector_from_irq(irq, false)).into(),
        );
        entry.set(
            32,
            32,
            read_reg(ioapic, encode_selector_from_irq(irq, true)).into(),
        );
        entry
    }

    fn write_entry(ioapic: &mut Ioapic, irq: usize, entry: RedirectionTableEntry) {
        write_reg(
            ioapic,
            encode_selector_from_irq(irq, false),
            entry.get(0, 32) as u32,
        );
        write_reg(
            ioapic,
            encode_selector_from_irq(irq, true),
            entry.get(32, 32) as u32,
        );
    }

    fn set_up_redirection_table_entry(ioapic: &mut Ioapic, irq: usize, trigger_mode: TriggerMode) {
        let mut entry = RedirectionTableEntry::new();
        entry.set_vector(DEFAULT_DESTINATION_ID);
        entry.set_delivery_mode(DeliveryMode::Startup);
        entry.set_delivery_status(DeliveryStatus::Pending);
        entry.set_dest_id(DEFAULT_VECTOR);
        entry.set_trigger_mode(trigger_mode);
        write_entry(ioapic, irq, entry);
    }

    fn set_mask(ioapic: &mut Ioapic, irq: usize, mask: bool) {
        let mut entry = read_entry(ioapic, irq);
        entry.set_interrupt_mask(mask);
        write_entry(ioapic, irq, entry);
    }

    #[test]
    fn write_read_ioregsel() {
        let mut ioapic = self::new();
        let data_write = [0x0f, 0xf0, 0x01, 0xff];
        let mut data_read = [0; 4];

        for i in 0..data_write.len() {
            ioapic.write(IOREGSEL_OFF.into(), &data_write[i..i + 1]);
            ioapic.read(IOREGSEL_OFF.into(), &mut data_read[i..i + 1]);
            assert_eq!(data_write[i], data_read[i]);
        }
    }

    // Verify that version register is actually read-only.
    #[test]
    fn write_read_ioaic_reg_version() {
        let mut ioapic = self::new();
        let before = read_reg(&mut ioapic, IOAPIC_REG_VERSION);
        let data_write = !before;

        write_reg(&mut ioapic, IOAPIC_REG_VERSION, data_write);
        assert_eq!(read_reg(&mut ioapic, IOAPIC_REG_VERSION), before);
    }

    // Verify that only bits 27:24 of the IOAPICID are readable/writable.
    #[test]
    fn write_read_ioapic_reg_id() {
        let mut ioapic = self::new();

        write_reg(&mut ioapic, IOAPIC_REG_ID, 0x1f3e5d7c);
        assert_eq!(read_reg(&mut ioapic, IOAPIC_REG_ID), 0x0f000000);
    }

    // Write to read-only register IOAPICARB.
    #[test]
    fn write_read_ioapic_arbitration_id() {
        let mut ioapic = self::new();

        let data_write_id = 0x1f3e5d7c;
        let expected_result = 0x0f000000;

        // Write to IOAPICID.  This should also change IOAPICARB.
        write_reg(&mut ioapic, IOAPIC_REG_ID, data_write_id);

        // Read IOAPICARB
        assert_eq!(
            read_reg(&mut ioapic, IOAPIC_REG_ARBITRATION_ID),
            expected_result
        );

        // Try to write to IOAPICARB and verify unchanged result.
        write_reg(&mut ioapic, IOAPIC_REG_ARBITRATION_ID, !data_write_id);
        assert_eq!(
            read_reg(&mut ioapic, IOAPIC_REG_ARBITRATION_ID),
            expected_result
        );
    }

    #[test]
    #[should_panic(expected = "index out of bounds: the len is 24 but the index is 24")]
    fn service_invalid_irq() {
        let mut ioapic = self::new();
        ioapic.service_irq(kvm::NUM_IOAPIC_PINS, false);
    }

    // Test a level triggered IRQ interrupt.
    #[test]
    fn service_level_irq() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        // TODO(mutexlox): Check that interrupt is fired once.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
    }

    #[test]
    fn service_multiple_level_irqs() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);
        // TODO(mutexlox): Check that interrupt is fired twice.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
        ioapic.end_of_interrupt(DEFAULT_DESTINATION_ID);
        ioapic.service_irq(irq, true);
    }

    // Test multiple level interrupts without an EOI and verify that only one interrupt is
    // delivered.
    #[test]
    fn coalesce_multiple_level_irqs() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        // TODO(mutexlox): Test that only one interrupt is delivered.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
        ioapic.service_irq(irq, true);
    }

    // Test multiple RTC interrupts without an EOI and verify that only one interrupt is delivered.
    #[test]
    fn coalesce_multiple_rtc_irqs() {
        let irq = RTC_IRQ;
        let mut ioapic = set_up_with_irq(irq, TriggerMode::Edge);

        // TODO(mutexlox): Verify that only one IRQ is delivered.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
        ioapic.service_irq(irq, true);
    }

    // Test that a level interrupt that has been coalesced is re-raised if a guest issues an
    // EndOfInterrupt after the interrupt was coalesced while the line  is still asserted.
    #[test]
    fn reinject_level_interrupt() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        // TODO(mutexlox): Verify that only one IRQ is delivered.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
        ioapic.service_irq(irq, true);

        // TODO(mutexlox): Verify that this last interrupt occurs as a result of the EOI, rather
        // than in response to the last service_irq.
        ioapic.end_of_interrupt(DEFAULT_DESTINATION_ID);
    }

    #[test]
    fn service_edge_triggered_irq() {
        let (mut ioapic, irq) = set_up(TriggerMode::Edge);

        // TODO(mutexlox): Verify that one interrupt is delivered.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, true); // Repeated asserts before a deassert should be ignored.
        ioapic.service_irq(irq, false);
    }

    // Verify that the state of an edge-triggered interrupt is properly tracked even when the
    // interrupt is disabled.
    #[test]
    fn edge_trigger_unmask_test() {
        let (mut ioapic, irq) = set_up(TriggerMode::Edge);

        // TODO(mutexlox): Expect an IRQ.

        ioapic.service_irq(irq, true);

        set_mask(&mut ioapic, irq, true);
        ioapic.service_irq(irq, false);

        // No interrupt triggered while masked.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);

        set_mask(&mut ioapic, irq, false);

        // TODO(mutexlox): Expect another interrupt.
        // Interrupt triggered while unmasked, even though when it was masked the level was high.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
    }

    // Verify that a level-triggered interrupt that is triggered while masked will fire once the
    // interrupt is unmasked.
    #[test]
    fn level_trigger_unmask_test() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        set_mask(&mut ioapic, irq, true);
        ioapic.service_irq(irq, true);

        // TODO(mutexlox): expect an interrupt after this.
        set_mask(&mut ioapic, irq, false);
    }

    // Verify that multiple asserts before a deassert are ignored even if there's an EOI between
    // them.
    #[test]
    fn end_of_interrupt_edge_triggered_irq() {
        let (mut ioapic, irq) = set_up(TriggerMode::Edge);

        // TODO(mutexlox): Expect 1 interrupt.
        ioapic.service_irq(irq, true);
        ioapic.end_of_interrupt(DEFAULT_DESTINATION_ID);
        // Repeated asserts before a de-assert should be ignored.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
    }

    // Send multiple edge-triggered interrupts in a row.
    #[test]
    fn service_multiple_edge_irqs() {
        let (mut ioapic, irq) = set_up(TriggerMode::Edge);

        ioapic.service_irq(irq, true);
        // TODO(mutexlox): Verify that an interrupt occurs here.
        ioapic.service_irq(irq, false);

        ioapic.service_irq(irq, true);
        // TODO(mutexlox): Verify that an interrupt occurs here.
        ioapic.service_irq(irq, false);
    }

    // Test an interrupt line with negative polarity.
    #[test]
    fn service_negative_polarity_irq() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        let mut entry = read_entry(&mut ioapic, irq);
        entry.set_polarity(1);
        write_entry(&mut ioapic, irq, entry);

        // TODO(mutexlox): Expect an interrupt to fire.
        ioapic.service_irq(irq, false);
    }

    // Ensure that remote IRR can't be edited via mmio.
    #[test]
    fn remote_irr_read_only() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        ioapic.redirect_table[irq].set_remote_irr(true);

        let mut entry = read_entry(&mut ioapic, irq);
        entry.set_remote_irr(false);
        write_entry(&mut ioapic, irq, entry);

        assert_eq!(read_entry(&mut ioapic, irq).get_remote_irr(), true);
    }

    #[test]
    fn delivery_status_read_only() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        ioapic.redirect_table[irq].set_delivery_status(DeliveryStatus::Pending);

        let mut entry = read_entry(&mut ioapic, irq);
        entry.set_delivery_status(DeliveryStatus::Idle);
        write_entry(&mut ioapic, irq, entry);

        assert_eq!(
            read_entry(&mut ioapic, irq).get_delivery_status(),
            DeliveryStatus::Pending
        );
    }

    #[test]
    fn level_to_edge_transition_clears_remote_irr() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        ioapic.redirect_table[irq].set_remote_irr(true);

        let mut entry = read_entry(&mut ioapic, irq);
        entry.set_trigger_mode(TriggerMode::Edge);
        write_entry(&mut ioapic, irq, entry);

        assert_eq!(read_entry(&mut ioapic, irq).get_remote_irr(), false);
    }

    #[test]
    fn masking_preserves_remote_irr() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        ioapic.redirect_table[irq].set_remote_irr(true);

        set_mask(&mut ioapic, irq, true);
        set_mask(&mut ioapic, irq, false);

        assert_eq!(read_entry(&mut ioapic, irq).get_remote_irr(), true);
    }

    // Test reconfiguration racing with EOIs.
    #[test]
    fn reconfiguration_race() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        // Fire one level-triggered interrupt.
        // TODO(mutexlox): Check that it fires.
        ioapic.service_irq(irq, true);

        // Read the redirection table entry before the EOI...
        let mut entry = read_entry(&mut ioapic, irq);
        entry.set_trigger_mode(TriggerMode::Edge);

        ioapic.service_irq(irq, false);
        ioapic.end_of_interrupt(DEFAULT_DESTINATION_ID);

        // ... and write back that (modified) value.
        write_entry(&mut ioapic, irq, entry);

        // Fire one *edge* triggered interrupt
        // TODO(mutexlox): Assert that the interrupt fires once.
        ioapic.service_irq(irq, true);
        ioapic.service_irq(irq, false);
    }

    // Ensure that swapping to edge triggered and back clears the remote irr bit.
    #[test]
    fn implicit_eoi() {
        let (mut ioapic, irq) = set_up(TriggerMode::Level);

        // Fire one level-triggered interrupt.
        ioapic.service_irq(irq, true);
        // TODO(mutexlox): Verify that one interrupt was fired.
        ioapic.service_irq(irq, false);

        // Do an implicit EOI by cycling between edge and level triggered.
        let mut entry = read_entry(&mut ioapic, irq);
        entry.set_trigger_mode(TriggerMode::Edge);
        write_entry(&mut ioapic, irq, entry);
        entry.set_trigger_mode(TriggerMode::Level);
        write_entry(&mut ioapic, irq, entry);

        // Fire one level-triggered interrupt.
        ioapic.service_irq(irq, true);
        // TODO(mutexlox): Verify that one interrupt fires.
        ioapic.service_irq(irq, false);
    }

    #[test]
    fn set_redirection_entry_by_bits() {
        let mut entry = RedirectionTableEntry::new();
        //                                                          destination_mode
        //                                                         polarity |
        //                                                  trigger_mode |  |
        //                                                             | |  |
        // 0011 1010 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 1001 0110 0101 1111
        // |_______| |______________________________________________||  | |  |_| |_______|
        //  dest_id                      reserved                    |  | |   |    vector
        //                                               interrupt_mask | |   |
        //                                                     remote_irr |   |
        //                                                    delivery_status |
        //                                                              delivery_mode
        entry.set(0, 64, 0x3a0000000000965f);
        assert_eq!(entry.get_vector(), 0x5f);
        assert_eq!(entry.get_delivery_mode(), DeliveryMode::Startup);
        assert_eq!(entry.get_dest_mode(), DestinationMode::Physical);
        assert_eq!(entry.get_delivery_status(), DeliveryStatus::Pending);
        assert_eq!(entry.get_polarity(), 0);
        assert_eq!(entry.get_remote_irr(), false);
        assert_eq!(entry.get_trigger_mode(), TriggerMode::Level);
        assert_eq!(entry.get_interrupt_mask(), false);
        assert_eq!(entry.get_reserved(), 0);
        assert_eq!(entry.get_dest_id(), 0x3a);

        let (mut ioapic, irq) = set_up(TriggerMode::Edge);
        write_entry(&mut ioapic, irq, entry);
        assert_eq!(
            read_entry(&mut ioapic, irq).get_trigger_mode(),
            TriggerMode::Level
        );

        // TODO(mutexlox): Verify that this actually fires an interrupt.
        ioapic.service_irq(irq, true);
    }
}