// Copyright 2020 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use std::arch::x86_64::CpuidResult;
use std::arch::x86_64::__cpuid;
use std::arch::x86_64::__cpuid_count;
use std::collections::BTreeMap;
use std::sync::Arc;

use acpi_tables::aml;
use acpi_tables::facs::FACS;
use acpi_tables::rsdp::RSDP;
use acpi_tables::sdt::SDT;
use arch::CpuSet;
use arch::VcpuAffinity;
use base::error;
use base::warn;
use devices::ACPIPMResource;
use devices::PciAddress;
use devices::PciInterruptPin;
use devices::PciRoot;
use sync::Mutex;
use vm_memory::GuestAddress;
use vm_memory::GuestMemory;
use zerocopy::AsBytes;
use zerocopy::FromBytes;
use zerocopy::FromZeroes;

pub struct AcpiDevResource {
    pub amls: Vec<u8>,
    pub pm_iobase: u64,
    pub pm: Arc<Mutex<ACPIPMResource>>,
    /// Additional system descriptor tables.
    pub sdts: Vec<SDT>,
}

#[repr(C, packed)]
#[derive(Clone, Copy, Default, FromZeroes, FromBytes, AsBytes)]
struct GenericAddress {
    _space_id: u8,
    _bit_width: u8,
    _bit_offset: u8,
    _access_width: u8,
    _address: u64,
}

#[repr(C)]
#[derive(Clone, Copy, Default, AsBytes)]
struct LocalApic {
    _type: u8,
    _length: u8,
    _processor_id: u8,
    _apic_id: u8,
    _flags: u32,
}

#[repr(C)]
#[derive(Clone, Copy, Default, FromZeroes, FromBytes, AsBytes)]
struct Ioapic {
    _type: u8,
    _length: u8,
    _ioapic_id: u8,
    _reserved: u8,
    _apic_address: u32,
    _gsi_base: u32,
}

#[repr(C, packed)]
#[derive(Clone, Copy, Default, FromZeroes, FromBytes, AsBytes)]
struct IoapicInterruptSourceOverride {
    _type: u8,
    _length: u8,
    _bus: u8,
    _source: u8,
    _gsi: u32,
    _flags: u16,
}

#[repr(C)]
#[derive(Clone, Copy, Default, FromZeroes, FromBytes, AsBytes)]
struct Localx2Apic {
    _type: u8,
    _length: u8,
    _reserved: u16,
    _x2apic_id: u32,
    _flags: u32,
    _processor_id: u32,
}

// Space ID for GenericAddress
const ADR_SPACE_SYSTEM_IO: u8 = 1;

const OEM_REVISION: u32 = 1;
//DSDT
const DSDT_REVISION: u8 = 6;
// FADT
const FADT_LEN: u32 = 276;
const FADT_REVISION: u8 = 6;
const FADT_MINOR_REVISION: u8 = 3;
// FADT flags
const FADT_POWER_BUTTON: u32 = 1 << 4;
const _FADT_SLEEP_BUTTON: u32 = 1 << 5;
const FADT_RESET_REGISTER: u32 = 1 << 10;
const FADT_LOW_POWER_S2IDLE: u32 = 1 << 21;
// FADT fields offset
const FADT_FIELD_FACS_ADDR32: usize = 36;
const FADT_FIELD_DSDT_ADDR32: usize = 40;
pub const FADT_FIELD_SCI_INTERRUPT: usize = 46;
const FADT_FIELD_SMI_COMMAND: usize = 48;
const FADT_FIELD_PM1A_EVENT_BLK_ADDR: usize = 56;
const FADT_FIELD_PM1B_EVENT_BLK_ADDR: usize = 60;
const FADT_FIELD_PM1A_CONTROL_BLK_ADDR: usize = 64;
const FADT_FIELD_PM1B_CONTROL_BLK_ADDR: usize = 68;
const FADT_FIELD_PM2_CONTROL_BLK_ADDR: usize = 72;
const FADT_FIELD_PM_TMR_BLK_ADDR: usize = 76;
const FADT_FIELD_GPE0_BLK_ADDR: usize = 80;
const FADT_FIELD_GPE1_BLK_ADDR: usize = 84;
const FADT_FIELD_PM1A_EVENT_BLK_LEN: usize = 88;
const FADT_FIELD_PM1A_CONTROL_BLK_LEN: usize = 89;
const FADT_FIELD_PM2_CONTROL_BLK_LEN: usize = 90;
const FADT_FIELD_PM_TMR_LEN: usize = 91;
const FADT_FIELD_GPE0_BLK_LEN: usize = 92;
const FADT_FIELD_GPE1_BLK_LEN: usize = 93;
const FADT_FIELD_GPE1_BASE: usize = 94;
const FADT_FIELD_RTC_DAY_ALARM: usize = 106;
const FADT_FIELD_RTC_MONTH_ALARM: usize = 107;
const FADT_FIELD_RTC_CENTURY: usize = 108;
const FADT_FIELD_FLAGS: usize = 112;
const FADT_FIELD_RESET_REGISTER: usize = 116;
const FADT_FIELD_RESET_VALUE: usize = 128;
const FADT_FIELD_MINOR_REVISION: usize = 131;
const FADT_FIELD_FACS_ADDR: usize = 132;
const FADT_FIELD_DSDT_ADDR: usize = 140;
const FADT_FIELD_X_PM1A_EVENT_BLK_ADDR: usize = 148;
const FADT_FIELD_X_PM1B_EVENT_BLK_ADDR: usize = 160;
const FADT_FIELD_X_PM1A_CONTROL_BLK_ADDR: usize = 172;
const FADT_FIELD_X_PM1B_CONTROL_BLK_ADDR: usize = 184;
const FADT_FIELD_X_PM2_CONTROL_BLK_ADDR: usize = 196;
const FADT_FIELD_X_PM_TMR_BLK_ADDR: usize = 208;
const FADT_FIELD_X_GPE0_BLK_ADDR: usize = 220;
const FADT_FIELD_X_GPE1_BLK_ADDR: usize = 232;
const FADT_FIELD_HYPERVISOR_ID: usize = 268;
// MADT
const MADT_LEN: u32 = 44;
const MADT_REVISION: u8 = 5;
// MADT fields offset
const MADT_FIELD_LAPIC_ADDR: usize = 36;
const MADT_FIELD_FLAGS: usize = 40;
// MADT flags
const MADT_FLAG_PCAT_COMPAT: u32 = 1 << 0;
// MADT structure offsets
const MADT_STRUCTURE_TYPE: usize = 0;
const MADT_STRUCTURE_LEN: usize = 1;
// MADT types
const MADT_TYPE_LOCAL_APIC: u8 = 0;
const MADT_TYPE_IO_APIC: u8 = 1;
const MADT_TYPE_INTERRUPT_SOURCE_OVERRIDE: u8 = 2;
const MADT_TYPE_LOCAL_X2APIC: u8 = 9;
// MADT flags
const MADT_ENABLED: u32 = 1;
const MADT_INT_POLARITY_ACTIVE_LOW: u16 = 0b11;
const MADT_INT_TRIGGER_LEVEL: u16 = 0b11 << 2;
// MADT compatibility
const MADT_MIN_LOCAL_APIC_ID: u32 = 255;
// XSDT
const XSDT_REVISION: u8 = 1;

const CPUID_LEAF0_EBX_CPUID_SHIFT: u32 = 24; // Offset of initial apic id.

// MCFG
const MCFG_LEN: u32 = 60;
const MCFG_REVISION: u8 = 1;
const MCFG_FIELD_BASE_ADDRESS: usize = 44;
const MCFG_FIELD_START_BUS_NUMBER: usize = 54;
const MCFG_FIELD_END_BUS_NUMBER: usize = 55;

const SSDT_REVISION: u8 = 2;
pub fn create_customize_ssdt(
    pci_root: Arc<Mutex<PciRoot>>,
    amls: BTreeMap<PciAddress, Vec<u8>>,
    gpe_scope_amls: BTreeMap<PciAddress, Vec<u8>>,
) -> Option<SDT> {
    if amls.is_empty() {
        return None;
    }

    let mut ssdt = SDT::new(
        *b"SSDT",
        acpi_tables::HEADER_LEN,
        SSDT_REVISION,
        *b"CROSVM",
        *b"CROSVMDT",
        OEM_REVISION,
    );

    for (address, children) in amls {
        if let Some(path) = pci_root.lock().acpi_path(&address) {
            ssdt.append_slice(&aml::Scope::raw((*path).into(), children));
        }
    }

    for children in gpe_scope_amls.values() {
        ssdt.append_slice(children);
    }

    Some(ssdt)
}

fn create_dsdt_table(amls: &[u8]) -> SDT {
    let mut dsdt = SDT::new(
        *b"DSDT",
        acpi_tables::HEADER_LEN,
        DSDT_REVISION,
        *b"CROSVM",
        *b"CROSVMDT",
        OEM_REVISION,
    );

    if !amls.is_empty() {
        dsdt.append_slice(amls);
    }

    dsdt
}

fn create_facp_table(sci_irq: u16, force_s2idle: bool) -> SDT {
    let mut facp = SDT::new(
        *b"FACP",
        FADT_LEN,
        FADT_REVISION,
        *b"CROSVM",
        *b"CROSVMDT",
        OEM_REVISION,
    );

    let mut fadt_flags: u32 = 0;

    if force_s2idle {
        fadt_flags |= FADT_LOW_POWER_S2IDLE;
    }

    facp.write(FADT_FIELD_FLAGS, fadt_flags);

    // SCI Interrupt
    facp.write(FADT_FIELD_SCI_INTERRUPT, sci_irq);

    facp.write(FADT_FIELD_MINOR_REVISION, FADT_MINOR_REVISION); // FADT minor version
    facp.write(FADT_FIELD_HYPERVISOR_ID, *b"CROSVM"); // Hypervisor Vendor Identity

    facp.write::<u8>(FADT_FIELD_RTC_CENTURY, devices::cmos::RTC_REG_CENTURY);
    facp.write::<u8>(FADT_FIELD_RTC_DAY_ALARM, devices::cmos::RTC_REG_ALARM_DAY);
    facp.write::<u8>(
        FADT_FIELD_RTC_MONTH_ALARM,
        devices::cmos::RTC_REG_ALARM_MONTH,
    );

    facp
}

// Write virtualized FADT fields
fn write_facp_overrides(
    facp: &mut SDT,
    facs_offset: GuestAddress,
    dsdt_offset: GuestAddress,
    pm_iobase: u32,
    reset_port: u32,
    reset_value: u8,
) {
    let fadt_flags: u32 = facp.read(FADT_FIELD_FLAGS);
    // indicate we support FADT RESET_REG
    facp.write(FADT_FIELD_FLAGS, fadt_flags | FADT_RESET_REGISTER);

    facp.write(FADT_FIELD_SMI_COMMAND, 0u32);
    facp.write(FADT_FIELD_FACS_ADDR32, 0u32);
    facp.write(FADT_FIELD_DSDT_ADDR32, 0u32);
    facp.write(FADT_FIELD_FACS_ADDR, facs_offset.0);
    facp.write(FADT_FIELD_DSDT_ADDR, dsdt_offset.0);

    // PM1A Event Block Address
    facp.write(FADT_FIELD_PM1A_EVENT_BLK_ADDR, pm_iobase);

    // PM1B Event Block Address (not supported)
    facp.write(FADT_FIELD_PM1B_EVENT_BLK_ADDR, 0u32);

    // PM1A Control Block Address
    facp.write(
        FADT_FIELD_PM1A_CONTROL_BLK_ADDR,
        pm_iobase + devices::acpi::ACPIPM_RESOURCE_EVENTBLK_LEN as u32,
    );

    // PM1B Control Block Address (not supported)
    facp.write(FADT_FIELD_PM1B_CONTROL_BLK_ADDR, 0u32);

    // PM2 Control Block Address (not supported)
    facp.write(FADT_FIELD_PM2_CONTROL_BLK_ADDR, 0u32);

    // PM Timer Control Block Address (not supported)
    facp.write(FADT_FIELD_PM_TMR_BLK_ADDR, 0u32);

    // GPE0 Block Address
    facp.write(
        FADT_FIELD_GPE0_BLK_ADDR,
        pm_iobase + devices::acpi::ACPIPM_RESOURCE_EVENTBLK_LEN as u32 + 4,
    );

    // GPE1 Block Address (not supported)
    facp.write(FADT_FIELD_GPE1_BLK_ADDR, 0u32);

    // PM1 Event Block Length
    facp.write(
        FADT_FIELD_PM1A_EVENT_BLK_LEN,
        devices::acpi::ACPIPM_RESOURCE_EVENTBLK_LEN,
    );

    // PM1 Control Block Length
    facp.write(
        FADT_FIELD_PM1A_CONTROL_BLK_LEN,
        devices::acpi::ACPIPM_RESOURCE_CONTROLBLK_LEN,
    );

    // PM2 Control Block Length (not supported)
    facp.write(FADT_FIELD_PM2_CONTROL_BLK_LEN, 0u8);

    // PM Timer Control Block Length (not supported)
    facp.write(FADT_FIELD_PM_TMR_LEN, 0u8);

    // GPE0 Block Length
    facp.write(
        FADT_FIELD_GPE0_BLK_LEN,
        devices::acpi::ACPIPM_RESOURCE_GPE0_BLK_LEN,
    );

    // GPE1 Block Length (not supported)
    facp.write(FADT_FIELD_GPE1_BLK_LEN, 0u8);

    // GPE1 Base (not supported)
    facp.write(FADT_FIELD_GPE1_BASE, 0u8);

    // PM1A Extended Event Block Address (not supported)
    facp.write(
        FADT_FIELD_X_PM1A_EVENT_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // PM1B Extended Event Block Address (not supported)
    facp.write(
        FADT_FIELD_X_PM1B_EVENT_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // PM1A Extended Control Block Address (not supported)
    facp.write(
        FADT_FIELD_X_PM1A_CONTROL_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // PM1B Extended Control Block Address (not supported)
    facp.write(
        FADT_FIELD_X_PM1B_CONTROL_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // PM2 Extended Control Block Address (not supported)
    facp.write(
        FADT_FIELD_X_PM2_CONTROL_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // PM Timer Extended Control Block Address (not supported)
    facp.write(
        FADT_FIELD_X_PM_TMR_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // GPE0 Extended Address (not supported)
    facp.write(
        FADT_FIELD_X_GPE0_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // GPE1 Extended Address (not supported)
    facp.write(
        FADT_FIELD_X_GPE1_BLK_ADDR,
        GenericAddress {
            ..Default::default()
        },
    );

    // Reset register
    facp.write(
        FADT_FIELD_RESET_REGISTER,
        GenericAddress {
            _space_id: ADR_SPACE_SYSTEM_IO,
            _bit_width: 8,
            _bit_offset: 0,
            _access_width: 1,
            _address: reset_port.into(),
        },
    );
    facp.write(FADT_FIELD_RESET_VALUE, reset_value);
}

fn next_offset(offset: GuestAddress, len: u64) -> Option<GuestAddress> {
    // Enforce 64-byte allocation alignment.
    match len % 64 {
        0 => offset.checked_add(len),
        x => offset.checked_add(len.checked_add(64 - x)?),
    }
}

fn sync_acpi_id_from_cpuid(
    madt: &mut SDT,
    cpus: BTreeMap<usize, CpuSet>,
    apic_ids: &mut Vec<usize>,
) -> base::Result<()> {
    let cpu_set = match base::get_cpu_affinity() {
        Err(e) => {
            error!("Failed to get CPU affinity: {} when create MADT", e);
            return Err(e);
        }
        Ok(c) => c,
    };

    for (vcpu, pcpu) in cpus {
        let mut has_leafb = false;
        let mut get_apic_id = false;
        let mut apic_id: u8 = 0;

        if let Err(e) = base::set_cpu_affinity(pcpu) {
            error!("Failed to set CPU affinity: {} when create MADT", e);
            return Err(e);
        }

        // SAFETY:
        // Safe because we pass 0 and 0 for this call and the host supports the
        // `cpuid` instruction
        let mut cpuid_entry: CpuidResult = unsafe { __cpuid_count(0, 0) };

        if cpuid_entry.eax >= 0xB {
            // SAFETY:
            // Safe because we pass 0xB and 0 for this call and the host supports the
            // `cpuid` instruction
            cpuid_entry = unsafe { __cpuid_count(0xB, 0) };

            if cpuid_entry.ebx != 0 {
                // MADT compatibility: (ACPI Spec v6.4) On some legacy OSes,
                // Logical processors with APIC ID values less than 255 (whether in
                // XAPIC or X2APIC mode) must use the Processor Local APIC structure.
                if cpuid_entry.edx < MADT_MIN_LOCAL_APIC_ID {
                    apic_id = cpuid_entry.edx as u8;
                    get_apic_id = true;
                } else {
                    // (ACPI Spec v6.4) When using the X2APIC, logical processors are
                    // required to have a processor device object in the DSDT and must
                    // convey the processor’s APIC information to OSPM using the Processor
                    // Local X2APIC structure.
                    // Now vCPUs use the DSDT passthrougt from host and the same APIC ID as
                    // the physical CPUs. Both of them should meet ACPI specifications on
                    // the host.
                    has_leafb = true;

                    let x2apic = Localx2Apic {
                        _type: MADT_TYPE_LOCAL_X2APIC,
                        _length: std::mem::size_of::<Localx2Apic>() as u8,
                        _x2apic_id: cpuid_entry.edx,
                        _flags: MADT_ENABLED,
                        _processor_id: (vcpu + 1) as u32,
                        ..Default::default()
                    };
                    madt.append(x2apic);
                    apic_ids.push(cpuid_entry.edx as usize);
                }
            }
        }

        if !has_leafb {
            if !get_apic_id {
                // SAFETY:
                // Safe because we pass 1 for this call and the host supports the
                // `cpuid` instruction
                cpuid_entry = unsafe { __cpuid(1) };
                apic_id = (cpuid_entry.ebx >> CPUID_LEAF0_EBX_CPUID_SHIFT & 0xff) as u8;
            }

            let apic = LocalApic {
                _type: MADT_TYPE_LOCAL_APIC,
                _length: std::mem::size_of::<LocalApic>() as u8,
                _processor_id: vcpu as u8,
                _apic_id: apic_id,
                _flags: MADT_ENABLED,
            };
            madt.append(apic);
            apic_ids.push(apic_id as usize);
        }
    }

    if let Err(e) = base::set_cpu_affinity(cpu_set) {
        error!("Failed to reset CPU affinity: {} when create MADT", e);
        return Err(e);
    }

    Ok(())
}

/// Create ACPI tables and return the RSDP.
/// The basic tables DSDT/FACP/MADT/XSDT are constructed in this function.
/// # Arguments
///
/// * `guest_mem` - The guest memory where the tables will be stored.
/// * `num_cpus` - Used to construct the MADT.
/// * `sci_irq` - Used to fill the FACP SCI_INTERRUPT field, which is going to be used by the ACPI
///   drivers to register sci handler.
/// * `acpi_dev_resource` - resouces needed by the ACPI devices for creating tables.
/// * `host_cpus` - The CPU affinity per CPU used to get corresponding CPUs' apic id and set these
///   apic id in MADT if `--host-cpu-topology` option is set.
/// * `apic_ids` - The apic id for vCPU will be sent to KVM by KVM_CREATE_VCPU ioctl.
/// * `pci_rqs` - PCI device to IRQ number assignments as returned by `arch::generate_pci_root()`
///   (device address, IRQ number, and PCI interrupt pin assignment).
/// * `pcie_cfg_mmio` - Base address for the pcie enhanced configuration access mechanism
/// * `max_bus` - Max bus number in MCFG table

pub fn create_acpi_tables(
    guest_mem: &GuestMemory,
    num_cpus: u8,
    sci_irq: u32,
    reset_port: u32,
    reset_value: u8,
    acpi_dev_resource: &AcpiDevResource,
    host_cpus: Option<VcpuAffinity>,
    apic_ids: &mut Vec<usize>,
    pci_irqs: &[(PciAddress, u32, PciInterruptPin)],
    pcie_cfg_mmio: u64,
    max_bus: u8,
    force_s2idle: bool,
) -> Option<GuestAddress> {
    // RSDP is at the HI RSDP WINDOW
    let rsdp_offset = GuestAddress(super::ACPI_HI_RSDP_WINDOW_BASE);
    let facs_offset = next_offset(rsdp_offset, RSDP::len() as u64)?;
    let mut offset = next_offset(facs_offset, FACS::len() as u64)?;
    let mut dsdt_offset: Option<GuestAddress> = None;
    let mut tables: Vec<u64> = Vec::new();
    let mut facp: Option<SDT> = None;
    let mut host_madt: Option<SDT> = None;

    // User supplied System Description Tables, e.g. SSDT.
    for sdt in acpi_dev_resource.sdts.iter() {
        if sdt.is_signature(b"FACP") {
            facp = Some(sdt.clone());
            continue;
        }
        if sdt.is_signature(b"APIC") {
            host_madt = Some(sdt.clone());
            continue;
        }
        guest_mem.write_at_addr(sdt.as_slice(), offset).ok()?;
        if sdt.is_signature(b"DSDT") {
            dsdt_offset = Some(offset);
        } else {
            tables.push(offset.0);
        }
        offset = next_offset(offset, sdt.len() as u64)?;
    }

    // FACS
    let facs = FACS::new();
    guest_mem.write_at_addr(facs.as_bytes(), facs_offset).ok()?;

    // DSDT
    let dsdt_offset = match dsdt_offset {
        Some(dsdt_offset) => dsdt_offset,
        None => {
            let dsdt_offset = offset;
            let dsdt = create_dsdt_table(&acpi_dev_resource.amls);
            guest_mem.write_at_addr(dsdt.as_slice(), offset).ok()?;
            offset = next_offset(offset, dsdt.len() as u64)?;
            dsdt_offset
        }
    };

    // FACP aka FADT
    let mut facp = facp.map_or_else(
        || create_facp_table(sci_irq as u16, force_s2idle),
        |facp| {
            let fadt_flags: u32 = facp.read(FADT_FIELD_FLAGS);
            if fadt_flags & FADT_POWER_BUTTON != 0 {
                warn!(
                    "Control Method Power Button is not supported. FADT flags = 0x{:x}",
                    fadt_flags
                );
            }
            facp
        },
    );

    write_facp_overrides(
        &mut facp,
        facs_offset,
        dsdt_offset,
        acpi_dev_resource.pm_iobase as u32,
        reset_port,
        reset_value,
    );

    guest_mem.write_at_addr(facp.as_slice(), offset).ok()?;
    tables.push(offset.0);
    offset = next_offset(offset, facp.len() as u64)?;

    // MADT
    let mut madt = SDT::new(
        *b"APIC",
        MADT_LEN,
        MADT_REVISION,
        *b"CROSVM",
        *b"CROSVMDT",
        OEM_REVISION,
    );
    madt.write(
        MADT_FIELD_LAPIC_ADDR,
        super::mptable::APIC_DEFAULT_PHYS_BASE,
    );
    // Our IrqChip implementations (the KVM in-kernel irqchip and the split irqchip) expose a pair
    // of PC-compatible 8259 PICs.
    madt.write(MADT_FIELD_FLAGS, MADT_FLAG_PCAT_COMPAT);

    match host_cpus {
        Some(VcpuAffinity::PerVcpu(cpus)) => {
            sync_acpi_id_from_cpuid(&mut madt, cpus, apic_ids).ok()?;
        }
        _ => {
            for cpu in 0..num_cpus {
                let apic = LocalApic {
                    _type: MADT_TYPE_LOCAL_APIC,
                    _length: std::mem::size_of::<LocalApic>() as u8,
                    _processor_id: cpu,
                    _apic_id: cpu,
                    _flags: MADT_ENABLED,
                };
                madt.append(apic);
                apic_ids.push(cpu as usize);
            }
        }
    }

    madt.append(Ioapic {
        _type: MADT_TYPE_IO_APIC,
        _length: std::mem::size_of::<Ioapic>() as u8,
        _apic_address: super::mptable::IO_APIC_DEFAULT_PHYS_BASE,
        ..Default::default()
    });

    // Add interrupt overrides for the PCI IRQs so that they are reported as level triggered, as
    // required by the PCI bus. The source and system GSI are identical, so this does not actually
    // override the mapping; we just use it to set the level-triggered flag.
    let mut unique_pci_irqs: Vec<u32> = pci_irqs.iter().map(|(_, irq_num, _)| *irq_num).collect();
    unique_pci_irqs.sort_unstable();
    unique_pci_irqs.dedup();
    for irq_num in unique_pci_irqs {
        madt.append(IoapicInterruptSourceOverride {
            _type: MADT_TYPE_INTERRUPT_SOURCE_OVERRIDE,
            _length: std::mem::size_of::<IoapicInterruptSourceOverride>() as u8,
            _bus: 0, // ISA
            _source: irq_num as u8,
            _gsi: irq_num,
            _flags: MADT_INT_POLARITY_ACTIVE_LOW | MADT_INT_TRIGGER_LEVEL,
        });
    }

    if let Some(host_madt) = host_madt {
        let mut idx = MADT_LEN as usize;
        while idx + MADT_STRUCTURE_LEN < host_madt.len() {
            let struct_type = host_madt.as_slice()[idx + MADT_STRUCTURE_TYPE];
            let struct_len = host_madt.as_slice()[idx + MADT_STRUCTURE_LEN] as usize;
            if struct_type == MADT_TYPE_INTERRUPT_SOURCE_OVERRIDE {
                if idx + struct_len <= host_madt.len() {
                    madt.append_slice(&host_madt.as_slice()[idx..(idx + struct_len)]);
                } else {
                    error!("Malformed host MADT");
                }
            }
            idx += struct_len;
        }
    }

    guest_mem.write_at_addr(madt.as_slice(), offset).ok()?;
    tables.push(offset.0);
    offset = next_offset(offset, madt.len() as u64)?;

    // MCFG
    let mut mcfg = SDT::new(
        *b"MCFG",
        MCFG_LEN,
        MCFG_REVISION,
        *b"CROSVM",
        *b"CROSVMDT",
        OEM_REVISION,
    );
    mcfg.write(MCFG_FIELD_BASE_ADDRESS, pcie_cfg_mmio);
    mcfg.write(MCFG_FIELD_START_BUS_NUMBER, 0_u8);
    mcfg.write(MCFG_FIELD_END_BUS_NUMBER, max_bus);

    guest_mem.write_at_addr(mcfg.as_slice(), offset).ok()?;
    tables.push(offset.0);
    offset = next_offset(offset, madt.len() as u64)?;

    // XSDT
    let mut xsdt = SDT::new(
        *b"XSDT",
        acpi_tables::HEADER_LEN,
        XSDT_REVISION,
        *b"CROSVM",
        *b"CROSVMDT",
        OEM_REVISION,
    );
    for table in tables {
        xsdt.append(table);
    }

    guest_mem.write_at_addr(xsdt.as_slice(), offset).ok()?;

    // RSDP
    let rsdp = RSDP::new(*b"CROSVM", offset.0);
    guest_mem.write_at_addr(rsdp.as_bytes(), rsdp_offset).ok()?;

    Some(rsdp_offset)
}

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

    #[test]
    fn facp_table_creation() {
        let sci_irq: u16 = 5;
        let force_s2idle = true;
        let facp = create_facp_table(sci_irq, force_s2idle);

        assert_eq!(facp.read::<u32>(FADT_FIELD_FLAGS), FADT_LOW_POWER_S2IDLE);
        assert_eq!(facp.read::<u16>(FADT_FIELD_SCI_INTERRUPT), sci_irq);
        assert_eq!(
            facp.read::<u8>(FADT_FIELD_MINOR_REVISION),
            FADT_MINOR_REVISION
        );
        assert_eq!(facp.read::<[u8; 6]>(FADT_FIELD_HYPERVISOR_ID), *b"CROSVM");
        assert_eq!(
            facp.read::<u8>(FADT_FIELD_RTC_CENTURY),
            devices::cmos::RTC_REG_CENTURY
        );
        assert_eq!(
            facp.read::<u8>(FADT_FIELD_RTC_DAY_ALARM),
            devices::cmos::RTC_REG_ALARM_DAY
        );
        assert_eq!(
            facp.read::<u8>(FADT_FIELD_RTC_MONTH_ALARM),
            devices::cmos::RTC_REG_ALARM_MONTH
        );
    }
}