// 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.
//
// Copyright © 2019 Intel Corporation
//
// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
//
// 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::BusDevice;
use byteorder::{ByteOrder, LittleEndian};
use kvm_bindings::kvm_msi;
use kvm_ioctls::VmFd;
use std::result;
use std::sync::Arc;
use vm_memory::GuestAddress;

#[derive(Debug)]
pub enum Error {
    /// Failed to send an interrupt.
    InterruptFailed(kvm_ioctls::Error),
    /// Invalid destination mode.
    InvalidDestinationMode,
    /// Invalid trigger mode.
    InvalidTriggerMode,
    /// Invalid delivery mode.
    InvalidDeliveryMode,
}

type Result<T> = result::Result<T, Error>;

// I/O REDIRECTION TABLE REGISTER
//
// There are 24 I/O Redirection Table entry registers. Each register is a
// dedicated entry for each interrupt input signal. Each register is 64 bits
// split between two 32 bits registers as follow:
//
// 63-56: Destination Field - R/W
// 55-17: Reserved
// 16:    Interrupt Mask - R/W
// 15:    Trigger Mode - R/W
// 14:    Remote IRR - RO
// 13:    Interrupt Input Pin Polarity - R/W
// 12:    Delivery Status - RO
// 11:    Destination Mode - R/W
// 10-8:  Delivery Mode - R/W
// 7-0:   Interrupt Vector - R/W
pub type RedirectionTableEntry = u64;

fn vector(entry: RedirectionTableEntry) -> u8 {
    (entry & 0xffu64) as u8
}
fn delivery_mode(entry: RedirectionTableEntry) -> u8 {
    ((entry >> 8) & 0x7u64) as u8
}
fn destination_mode(entry: RedirectionTableEntry) -> u8 {
    ((entry >> 11) & 0x1u64) as u8
}
fn remote_irr(entry: RedirectionTableEntry) -> u8 {
    ((entry >> 14) & 0x1u64) as u8
}
fn trigger_mode(entry: RedirectionTableEntry) -> u8 {
    ((entry >> 15) & 0x1u64) as u8
}
fn interrupt_mask(entry: RedirectionTableEntry) -> u8 {
    ((entry >> 16) & 0x1u64) as u8
}
fn destination_field_physical(entry: RedirectionTableEntry) -> u8 {
    ((entry >> 56) & 0xfu64) as u8
}
fn destination_field_logical(entry: RedirectionTableEntry) -> u8 {
    ((entry >> 56) & 0xffu64) as u8
}
fn set_delivery_status(entry: &mut RedirectionTableEntry, val: u8) {
    // Clear bit 12
    *entry &= 0xffff_ffff_ffff_efff;
    // Set it with the expected value
    *entry |= u64::from(val & 0x1) << 12;
}
fn set_remote_irr(entry: &mut RedirectionTableEntry, val: u8) {
    // Clear bit 14
    *entry &= 0xffff_ffff_ffff_bfff;
    // Set it with the expected value
    *entry |= u64::from(val & 0x1) << 14;
}

pub struct MsiMessage {
    // Message Address Register
    //   31-20: Base address. Fixed value (0x0FEE)
    //   19-12: Destination ID
    //   11-4:  Reserved
    //   3:     Redirection Hint indication
    //   2:     Destination Mode
    //   1-0:   Reserved
    pub addr: u32,
    // Message Data Register
    //   32-16: Reserved
    //   15:    Trigger Mode. 0 = Edge, 1 = Level
    //   14:    Level. 0 = Deassert, 1 = Assert
    //   13-11: Reserved
    //   10-8:  Delivery Mode
    //   7-0:   Vector
    pub data: u32,
}

pub const NUM_IOAPIC_PINS: usize = 24;
const IOAPIC_VERSION_ID: u32 = 0x0017_0011;

// 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 IOWIN_OFF: u8 = 0x10;
const IOWIN_SCALE: u8 = 0x2;
const REG_MAX_OFFSET: u8 = IOWIN_OFF + (NUM_IOAPIC_PINS as u8 * 2) - 1;

#[repr(u8)]
enum DestinationMode {
    Physical = 0,
    Logical = 1,
}

#[repr(u8)]
enum TriggerMode {
    Edge = 0,
    Level = 1,
}

#[repr(u8)]
enum DeliveryMode {
    Fixed = 0b000,
    Lowest = 0b001,
    SMI = 0b010,        // System management interrupt
    RemoteRead = 0b011, // This is no longer supported by intel.
    NMI = 0b100,        // Non maskable interrupt
    Init = 0b101,
    Startup = 0b110,
    External = 0b111,
}

/// 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,
    )
}

pub struct Ioapic {
    id: u32,
    reg_sel: u32,
    reg_entries: [RedirectionTableEntry; NUM_IOAPIC_PINS],
    vm_fd: Arc<VmFd>,
    apic_address: GuestAddress,
}

impl BusDevice for Ioapic {
    fn read(&mut self, _base: u64, offset: u64, data: &mut [u8]) {
        assert!(data.len() == 4);

        debug!("IOAPIC_R @ offset 0x{:x}", offset);

        let value: u32 = match offset as u8 {
            IOREGSEL_OFF => self.reg_sel,
            IOWIN_OFF => self.ioapic_read(),
            _ => {
                error!("IOAPIC: failed reading at offset {}", offset);
                return;
            }
        };

        LittleEndian::write_u32(data, value);
    }

    fn write(&mut self, _base: u64, offset: u64, data: &[u8]) {
        assert!(data.len() == 4);

        debug!("IOAPIC_W @ offset 0x{:x}", offset);

        let value = LittleEndian::read_u32(data);

        match offset as u8 {
            IOREGSEL_OFF => self.reg_sel = value,
            IOWIN_OFF => self.ioapic_write(value),
            _ => {
                error!("IOAPIC: failed writing at offset {}", offset);
            }
        }
    }
}

impl Ioapic {
    pub fn new(vm_fd: Arc<VmFd>, apic_address: GuestAddress) -> Ioapic {
        Ioapic {
            id: 0,
            reg_sel: 0,
            reg_entries: [0; NUM_IOAPIC_PINS],
            vm_fd,
            apic_address,
        }
    }

    // The ioapic must be informed about EOIs in order to deassert interrupts
    // already sent.
    pub fn end_of_interrupt(&mut self, vec: u8) {
        for i in 0..NUM_IOAPIC_PINS {
            let entry = &mut self.reg_entries[i];
            // Clear Remote IRR bit
            if vector(*entry) == vec && trigger_mode(*entry) == 1 {
                set_remote_irr(entry, 0);
            }
        }
    }

    // This should be called anytime an interrupt needs to be injected into the
    // running guest.
    pub fn service_irq(&mut self, irq: usize) -> Result<()> {
        let entry = &mut self.reg_entries[irq];

        // Don't inject the interrupt if the IRQ is masked
        if interrupt_mask(*entry) == 1 {
            return Ok(());
        }

        // Validate Destination Mode value, and retrieve Destination ID
        let destination_mode = destination_mode(*entry);
        let destination_id: u8 = match destination_mode {
            x if x == DestinationMode::Physical as u8 => destination_field_physical(*entry),
            x if x == DestinationMode::Logical as u8 => destination_field_logical(*entry),
            _ => return Err(Error::InvalidDestinationMode),
        };

        // When this bit is set, the message is directed to the processor with
        // the lowest interrupt priority among processors that can receive the
        // interrupt.
        let redirection_hint: u8 = 1;

        // Generate MSI message address
        let address_lo: u32 = self.apic_address.0 as u32
            | u32::from(destination_id) << 12
            | u32::from(redirection_hint) << 3
            | u32::from(destination_mode) << 2;

        // Validate Trigger Mode value
        let trigger_mode = trigger_mode(*entry);
        match trigger_mode {
            x if (x == TriggerMode::Edge as u8) || (x == TriggerMode::Level as u8) => {}
            _ => return Err(Error::InvalidTriggerMode),
        }

        // Validate Delivery Mode value
        let delivery_mode = delivery_mode(*entry);
        match delivery_mode {
            x if (x == DeliveryMode::Fixed as u8)
                || (x == DeliveryMode::Lowest as u8)
                || (x == DeliveryMode::SMI as u8)
                || (x == DeliveryMode::RemoteRead as u8)
                || (x == DeliveryMode::NMI as u8)
                || (x == DeliveryMode::Init as u8)
                || (x == DeliveryMode::Startup as u8)
                || (x == DeliveryMode::External as u8) => {}
            _ => return Err(Error::InvalidDeliveryMode),
        }

        // Generate MSI message data
        let data: u32 = u32::from(trigger_mode) << 15
            | u32::from(remote_irr(*entry)) << 14
            | u32::from(delivery_mode) << 8
            | u32::from(vector(*entry));

        let msi = kvm_msi {
            address_lo,
            address_hi: 0x0,
            data,
            flags: 0u32,
            devid: 0u32,
            pad: [0u8; 12],
        };

        match self.vm_fd.signal_msi(msi) {
            Ok(ret) => {
                if ret > 0 {
                    debug!("MSI message successfully delivered");
                    // If trigger mode is level sensitive, set the Remote IRR bit.
                    // It will be cleared when the EOI is received.
                    if trigger_mode == 1 {
                        set_remote_irr(entry, 1);
                    }
                    // Clear the Delivery Status bit
                    set_delivery_status(entry, 0);
                } else {
                    warn!("failed to deliver MSI message, blocked by guest");
                }
                Ok(())
            }
            Err(e) => Err(Error::InterruptFailed(e)),
        }
    }

    fn ioapic_write(&mut self, val: u32) {
        debug!("IOAPIC_W reg 0x{:x}, val 0x{:x}", self.reg_sel, val);

        match self.reg_sel as u8 {
            IOAPIC_REG_ID => self.id = (val >> 24) & 0xf,
            IOWIN_OFF..=REG_MAX_OFFSET => {
                let (index, is_high_bits) = decode_irq_from_selector(self.reg_sel as u8);
                if is_high_bits {
                    self.reg_entries[index] &= 0xffff_ffff;
                    self.reg_entries[index] |= u64::from(val) << 32;
                } else {
                    // Ensure not to override read-only bits:
                    // - Delivery Status (bit 12)
                    // - Remote IRR (bit 14)
                    self.reg_entries[index] &= 0xffff_ffff_0000_5000;
                    self.reg_entries[index] |= u64::from(val) & 0xffff_afff;
                }
            }
            _ => error!("IOAPIC: invalid write to register offset"),
        }
    }

    fn ioapic_read(&self) -> u32 {
        debug!("IOAPIC_R reg 0x{:x}", self.reg_sel);

        match self.reg_sel as u8 {
            IOAPIC_REG_VERSION => IOAPIC_VERSION_ID,
            IOAPIC_REG_ID | IOAPIC_REG_ARBITRATION_ID => (self.id & 0xf) << 24,
            IOWIN_OFF..=REG_MAX_OFFSET => {
                let (index, is_high_bits) = decode_irq_from_selector(self.reg_sel as u8);
                if is_high_bits {
                    (self.reg_entries[index] >> 32) as u32
                } else {
                    (self.reg_entries[index] & 0xffff_ffff) as u32
                }
            }
            _ => {
                error!("IOAPIC: invalid read from register offset");
                0
            }
        }
    }
}