ktstr 0.5.2

use anyhow::{Context, Result};
use kvm_bindings::{
    KVM_ARM_VCPU_PMU_V3_CTRL, KVM_ARM_VCPU_PMU_V3_INIT, KVM_ARM_VCPU_PMU_V3_IRQ,
    KVM_DEV_ARM_VGIC_CTRL_INIT, KVM_DEV_ARM_VGIC_GRP_ADDR, KVM_DEV_ARM_VGIC_GRP_CTRL,
    KVM_DEV_ARM_VGIC_GRP_NR_IRQS, KVM_IRQ_ROUTING_IRQCHIP, KVM_VGIC_V3_ADDR_TYPE_DIST,
    KVM_VGIC_V3_ADDR_TYPE_REDIST, KvmIrqRouting, kvm_create_device, kvm_device_attr,
    kvm_device_type_KVM_DEV_TYPE_ARM_VGIC_V3, kvm_irq_routing_entry,
    kvm_irq_routing_entry__bindgen_ty_1, kvm_irq_routing_irqchip,
};
use kvm_ioctls::{Cap, DeviceFd, Kvm, VcpuFd, VmFd};
use std::mem::ManuallyDrop;
use vm_memory::{GuestAddress, GuestMemoryMmap};

use crate::vmm::numa_mem::{NumaMemoryLayout, ReservationGuard};
use crate::vmm::topology::Topology;

// ---------------------------------------------------------------------------
// Memory layout — devices below DRAM, guest RAM above
// ---------------------------------------------------------------------------

/// Start of guest DRAM. All device MMIO regions live below this address.
pub(crate) const DRAM_START: u64 = 0x4000_0000; // 1 GB

/// GICv3 distributor MMIO base address.
pub(crate) const GIC_DIST_BASE: u64 = 0x0800_0000;

/// GICv3 distributor size: 64 KB.
pub(crate) const GIC_DIST_SIZE: u64 = 0x1_0000;

/// GICv3 redistributor base: immediately after the distributor.
/// Each redistributor occupies 128 KB (two 64 KB frames: RD_base + SGI_base).
pub(crate) const GIC_REDIST_BASE: u64 = GIC_DIST_BASE + GIC_DIST_SIZE;

/// Size per redistributor: 128 KB (RD_base + SGI_base).
pub(crate) const GIC_REDIST_SIZE_PER_CPU: u64 = 0x2_0000;

/// ns16550a serial MMIO base address. SPI 33.
pub(crate) const SERIAL_MMIO_BASE: u64 = 0x0900_0000;

/// ns16550a serial MMIO size: one 4 KB page covering the 8-byte register
/// window. KVM/OS accesses are 4-byte aligned; the page-sized region
/// keeps each UART on its own guest page.
pub(crate) const SERIAL_MMIO_SIZE: u64 = 0x1000;

/// Second serial for application output. SPI 34.
pub(crate) const SERIAL2_MMIO_BASE: u64 = SERIAL_MMIO_BASE + SERIAL_MMIO_SIZE;

/// Virtio-console MMIO base. Placed after the two serial regions.
pub(crate) const VIRTIO_CONSOLE_MMIO_BASE: u64 = SERIAL2_MMIO_BASE + SERIAL_MMIO_SIZE;

/// SPI interrupt for virtio-console. SPI 35.
pub(crate) const VIRTIO_CONSOLE_IRQ: u32 = 35;

/// Virtio-block MMIO base. Placed after virtio-console.
pub(crate) const VIRTIO_BLK_MMIO_BASE: u64 =
    VIRTIO_CONSOLE_MMIO_BASE + crate::vmm::virtio_console::VIRTIO_MMIO_SIZE;

/// SPI interrupt for virtio-block. SPI 36.
pub(crate) const VIRTIO_BLK_IRQ: u32 = 36;

/// Virtio-net MMIO base. Placed after virtio-block.
pub(crate) const VIRTIO_NET_MMIO_BASE: u64 =
    VIRTIO_BLK_MMIO_BASE + crate::vmm::virtio_blk::VIRTIO_MMIO_SIZE;

/// SPI interrupt for virtio-net. SPI 37.
pub(crate) const VIRTIO_NET_IRQ: u32 = 37;

/// Kernel Image load address. 2 MB aligned per arm64 boot protocol.
/// Relative to DRAM_START — the kernel is loaded at DRAM_START + text_offset,
/// but the PE loader base address must be DRAM_START (2 MB aligned).
pub(crate) const KERNEL_LOAD_ADDR: u64 = DRAM_START;

/// FDT maximum size: 2 MB. FDT is placed at the end of usable DRAM.
pub(crate) const FDT_MAX_SIZE: u64 = 0x20_0000;

/// Maximum command line length.
pub(crate) const CMDLINE_MAX: usize = 4096;

/// SPI interrupt numbers for the two serial ports.
/// GICv3 SPIs start at IRQ 32. These map to intid = 32 + N.
pub(crate) const SERIAL_IRQ: u32 = 33;
pub(crate) const SERIAL2_IRQ: u32 = 34;

/// PMU overflow interrupt — PPI number in the GIC PPI namespace (0..15).
/// PPI 7 is the standard arm,armv8-pmuv3 binding. The FDT pmu node
/// references PMU_PPI directly. KVM_ARM_VCPU_PMU_V3_IRQ expects the
/// global intid namespace (PPI + VGIC_NR_SGIS = 7 + 16 = 23), exposed
/// as PMU_INTID for the irq_is_ppi check in
/// arch/arm64/kvm/pmu-emul.c pmu_irq_is_valid.
pub(crate) const PMU_PPI: u32 = 7;
pub(crate) const PMU_INTID: u32 = PMU_PPI + 16;

/// Number of IRQs for the GIC. Must be a multiple of 32 and >= 64.
/// 128 covers SPIs 0-95, sufficient for serial + headroom.
const GIC_NR_IRQS: u32 = 128;

/// A KVM virtual machine with configured topology (aarch64).
#[allow(dead_code)]
pub struct KtstrKvm {
    pub kvm: ManuallyDrop<Kvm>,
    pub vm_fd: ManuallyDrop<VmFd>,
    pub vcpus: Vec<VcpuFd>,
    pub guest_mem: ManuallyDrop<GuestMemoryMmap>,
    pub topology: Topology,
    /// Per-node GPA layout used by FDT memory nodes and NUMA distance map.
    /// `None` in deferred mode before `allocate_and_register_memory()`.
    pub(crate) numa_layout: Option<NumaMemoryLayout>,
    pub has_immediate_exit: bool,
    /// True when the host KVM advertises Cap::ArmPmuV3. Threaded into
    /// FDT generation so the arm,armv8-pmuv3 node is only emitted when
    /// the kernel will actually deliver PMU events; on no-PMU hosts the
    /// guest pmuv3 driver would otherwise attach and fail noisily.
    pub has_pmu: bool,
    /// GICv3 device fd — held to keep the device alive.
    gic_fd: ManuallyDrop<DeviceFd>,
    /// Whether hugepages were requested at construction time.
    /// Stored so deferred memory allocation uses the same backing.
    use_hugepages: bool,
    /// Performance mode flag. Stored so deferred memory allocation
    /// can check hugepage availability fresh when memory_mb was
    /// unknown at construction time.
    performance_mode: bool,
    /// Owns the VA reservation for per-node MAP_FIXED mmaps.
    /// Drop munmaps the entire reservation.
    _reservation: Option<ReservationGuard>,
    /// RAII guards for COW-overlayed initramfs segments. Each guard
    /// holds the lz4 SHM fd with `LOCK_SH`; dropping it releases the
    /// flock and closes the fd. Must drop AFTER `_reservation` so the
    /// COW VMAs are torn down (via the reservation's munmap) before
    /// the flock is released — otherwise a concurrent writer could
    /// take `LOCK_EX` and truncate the segment while the guest still
    /// holds pages that fault through the backing file.
    pub(crate) cow_overlay_guards: Vec<crate::vmm::initramfs::CowOverlayGuard>,
}

impl Drop for KtstrKvm {
    fn drop(&mut self) {
        unsafe {
            // Ordered teardown: vCPU fds → GICv3 device fd → VM fd →
            // guest memory → VA reservation → COW flock guards → /dev/kvm.
            //
            // Closing VmFd triggers kvm_destroy_vm which calls
            // mmu_notifier_unregister (synchronous SRCU wait). All
            // KVM references to this process's page tables are removed
            // before the guest memory munmap fires, preventing stale
            // mmu_notifier callbacks from racing with the unmap.
            let vcpus = std::mem::take(&mut self.vcpus);
            drop(vcpus);
            ManuallyDrop::drop(&mut self.gic_fd);
            ManuallyDrop::drop(&mut self.vm_fd);
            ManuallyDrop::drop(&mut self.guest_mem);
            let reservation = self._reservation.take();
            drop(reservation);
            let cow_guards = std::mem::take(&mut self.cow_overlay_guards);
            drop(cow_guards);
            ManuallyDrop::drop(&mut self.kvm);
        }
    }
}

impl KtstrKvm {
    /// Create a new KVM VM with the given topology and memory size.
    pub fn new(topo: Topology, memory_mb: u32, performance_mode: bool) -> Result<Self> {
        Self::new_inner(topo, Some(memory_mb), false, performance_mode)
    }

    /// Create a new KVM VM with hugepage-backed guest memory.
    pub fn new_with_hugepages(
        topo: Topology,
        memory_mb: u32,
        performance_mode: bool,
    ) -> Result<Self> {
        Self::new_inner(topo, Some(memory_mb), true, performance_mode)
    }

    /// Create a KVM VM without allocating guest memory.
    ///
    /// Sets up /dev/kvm, VM fd, vCPUs, GICv3, and PMUv3 (when host
    /// supports) — none of which depend on guest memory size. Memory is
    /// allocated later via [`Self::allocate_and_register_memory`].
    pub fn new_deferred(
        topo: Topology,
        use_hugepages: bool,
        performance_mode: bool,
    ) -> Result<Self> {
        Self::new_inner(topo, None, use_hugepages, performance_mode)
    }

    /// Allocate guest memory and register it with KVM.
    ///
    /// Should be called exactly once on a VM created with
    /// `new_deferred`; calling twice unconditionally replaces the
    /// backing memory. Replaces the placeholder guest memory with a
    /// real allocation of `memory_mb` megabytes at DRAM_START and
    /// sets `numa_layout` to the computed per-node GPA layout.
    /// Re-checks hugepage availability when performance_mode is set,
    /// since memory_mb was unknown at construction time and
    /// `use_hugepages` may have been false.
    pub fn allocate_and_register_memory(&mut self, memory_mb: u32) -> Result<()> {
        let layout = NumaMemoryLayout::compute(&self.topology, memory_mb, DRAM_START)?;
        let alloc =
            layout.allocate_and_register(&self.vm_fd, self.use_hugepages, self.performance_mode)?;
        // SAFETY: guest_mem is ManuallyDrop — explicit drop before
        // replacement prevents leaking the placeholder mapping.
        unsafe { ManuallyDrop::drop(&mut self.guest_mem) };
        self.guest_mem = ManuallyDrop::new(alloc.guest_mem);
        self._reservation = Some(alloc.reservation);
        self.numa_layout = Some(layout);
        Ok(())
    }

    fn new_inner(
        topo: Topology,
        memory_mb: Option<u32>,
        use_hugepages: bool,
        performance_mode: bool,
    ) -> Result<Self> {
        let kvm = Kvm::new().context("open /dev/kvm")?;

        let has_immediate_exit = kvm.check_extension(Cap::ImmediateExit);

        let vm_fd = crate::vmm::create_vm_with_retry(&kvm)?;

        let (guest_mem, numa_layout, reservation) = match memory_mb {
            Some(mb) => {
                let layout = NumaMemoryLayout::compute(&topo, mb, DRAM_START)?;
                let alloc =
                    layout.allocate_and_register(&vm_fd, use_hugepages, performance_mode)?;
                (alloc.guest_mem, Some(layout), Some(alloc.reservation))
            }
            None => {
                let placeholder =
                    GuestMemoryMmap::<()>::from_ranges(&[(GuestAddress(DRAM_START), 4096)])
                        .context("allocate placeholder guest memory")?;
                (placeholder, None, None)
            }
        };

        // Create vCPUs. On aarch64, vCPUs must exist before GIC init.
        let total = topo.total_cpus();
        let mut vcpus = Vec::with_capacity(total as usize);

        let mut kvi = kvm_bindings::kvm_vcpu_init::default();
        vm_fd
            .get_preferred_target(&mut kvi)
            .context("get preferred target")?;
        kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_PSCI_0_2;
        // Enable pointer authentication if host supports it.
        // Shared libraries from the host (packed into the initramfs)
        // may contain PAC instructions when the toolchain defaults to
        // -mbranch-protection (e.g. Fedora 38+ aarch64). Without
        // these flags KVM traps PAC as UNDEF → guest SIGILL.
        if vm_fd.check_extension(kvm_ioctls::Cap::ArmPtrAuthAddress) {
            kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_PTRAUTH_ADDRESS;
        }
        if vm_fd.check_extension(kvm_ioctls::Cap::ArmPtrAuthGeneric) {
            kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_PTRAUTH_GENERIC;
        }
        // Enable PMUv3 emulation when the host supports it. Without this
        // bit set in vcpu_init, ID_AA64DFR0_EL1.PMUVer is forced to 0 and
        // sched_ext schedulers (scx_layered, scx_cosmos) that read
        // perf counters via BPF kfuncs see no available PMU.
        // Per arch/arm64/kvm/arm.c system_supported_vcpu_features, the
        // KVM_ARM_VCPU_PMU_V3 bit is silently masked out of
        // system_supported_vcpu_features() when !kvm_supports_guest_pmuv3,
        // so setting it on a no-PMU host returns -EINVAL. Gate via
        // KVM_CAP_ARM_PMU_V3.
        let pmu_supported = vm_fd.check_extension(Cap::ArmPmuV3);
        if pmu_supported {
            kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_PMU_V3;
        }

        for cpu_id in 0..total {
            // KVM_CREATE_VCPU allocates per-vCPU kernel state; map
            // EMFILE/ENOMEM to ResourceContention so the macro SKIPs
            // cleanly on host-resource pressure.
            let vcpu = vm_fd.create_vcpu(cpu_id as u64).map_err(|e| {
                crate::vmm::map_transient_to_contention(e, format!("create vCPU {cpu_id}"))
            })?;

            let mut vcpu_kvi = kvi;
            if cpu_id != 0 {
                vcpu_kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_POWER_OFF;
            }
            // KVM_ARM_VCPU_INIT allocates the per-vCPU register
            // file and finalises feature bits; ENOMEM under host
            // pressure is transient.
            vcpu.vcpu_init(&vcpu_kvi).map_err(|e| {
                crate::vmm::map_transient_to_contention(e, format!("init vCPU {cpu_id}"))
            })?;

            vcpus.push(vcpu);
        }

        // Override CLIDR_EL1 on each vCPU to match the host's real
        // cache topology. Must happen after vcpu_init and before FDT
        // creation so CLIDR and DT cache nodes agree on leaf counts.
        super::topology::override_clidr(&vcpus)
            .context("override CLIDR_EL1 to match host cache topology")?;

        // Create GICv3 via KVM_CREATE_DEVICE.
        let gic_fd = Self::create_gic(&vm_fd, total)?;

        // Set up GSI routing so irqfd works with the GICv3 device.
        // Map GSI N -> irqchip 0, pin N for the serial SPI IRQs.
        Self::setup_gsi_routing(&vm_fd)?;

        // Initialise PMUv3 per vcpu after GIC init. kvm_arm_pmu_v3_init
        // (arch/arm64/kvm/pmu-emul.c) requires vgic_initialized AND
        // kvm_arm_pmu_irq_initialized — i.e. KVM_ARM_VCPU_PMU_V3_IRQ
        // must be set before KVM_ARM_VCPU_PMU_V3_INIT. The IRQ value is
        // a PPI (16..32), shared across vcpus per pmu_irq_is_valid.
        if pmu_supported {
            Self::init_pmuv3(&vcpus)?;
        }

        Ok(KtstrKvm {
            kvm: ManuallyDrop::new(kvm),
            vm_fd: ManuallyDrop::new(vm_fd),
            vcpus,
            guest_mem: ManuallyDrop::new(guest_mem),
            topology: topo,
            numa_layout,
            has_immediate_exit,
            has_pmu: pmu_supported,
            gic_fd: ManuallyDrop::new(gic_fd),
            use_hugepages,
            performance_mode,
            _reservation: reservation,
            cow_overlay_guards: Vec::new(),
        })
    }

    /// Create and initialize a GICv3 interrupt controller.
    fn create_gic(vm_fd: &VmFd, num_cpus: u32) -> Result<DeviceFd> {
        let mut gic_device = kvm_create_device {
            type_: kvm_device_type_KVM_DEV_TYPE_ARM_VGIC_V3,
            fd: 0,
            flags: 0,
        };
        // KVM_CREATE_DEVICE allocates the GICv3 distributor +
        // redistributor tables. ENOMEM under host pressure is
        // transient — route through map_transient_to_contention.
        let gic_fd = vm_fd
            .create_device(&mut gic_device)
            .map_err(|e| crate::vmm::map_transient_to_contention(e, "create GICv3 device"))?;

        // Set number of IRQs.
        let nr_irqs: u32 = GIC_NR_IRQS;
        let nr_irqs_attr = kvm_device_attr {
            group: KVM_DEV_ARM_VGIC_GRP_NR_IRQS,
            attr: 0,
            addr: &nr_irqs as *const u32 as u64,
            flags: 0,
        };
        gic_fd
            .set_device_attr(&nr_irqs_attr)
            .context("set GIC nr_irqs")?;

        // Set distributor address.
        let dist_addr: u64 = GIC_DIST_BASE;
        let dist_attr = kvm_device_attr {
            group: KVM_DEV_ARM_VGIC_GRP_ADDR,
            attr: KVM_VGIC_V3_ADDR_TYPE_DIST as u64,
            addr: &dist_addr as *const u64 as u64,
            flags: 0,
        };
        gic_fd
            .set_device_attr(&dist_attr)
            .context("set GIC distributor address")?;

        // Set redistributor address.
        let redist_addr: u64 = GIC_REDIST_BASE;
        let redist_size = num_cpus as u64 * GIC_REDIST_SIZE_PER_CPU;
        anyhow::ensure!(
            GIC_REDIST_BASE + redist_size <= DRAM_START,
            "GIC redistributor region (ends at {:#x}) overlaps DRAM at {:#x} for {} CPUs",
            GIC_REDIST_BASE + redist_size,
            DRAM_START,
            num_cpus,
        );
        let redist_attr = kvm_device_attr {
            group: KVM_DEV_ARM_VGIC_GRP_ADDR,
            attr: KVM_VGIC_V3_ADDR_TYPE_REDIST as u64,
            addr: &redist_addr as *const u64 as u64,
            flags: 0,
        };
        gic_fd
            .set_device_attr(&redist_attr)
            .context("set GIC redistributor address")?;

        // Initialize the GIC. KVM_DEV_ARM_VGIC_CTRL_INIT allocates
        // the per-vcpu redistributor tables and finalises the
        // distributor; ENOMEM under host pressure is transient.
        let init_attr = kvm_device_attr {
            group: KVM_DEV_ARM_VGIC_GRP_CTRL,
            attr: KVM_DEV_ARM_VGIC_CTRL_INIT as u64,
            addr: 0,
            flags: 0,
        };
        gic_fd
            .set_device_attr(&init_attr)
            .map_err(|e| crate::vmm::map_transient_to_contention(e, "init GIC device"))?;

        Ok(gic_fd)
    }

    /// Set up GSI routing for irqfd.
    ///
    /// With GICv3 via KVM_CREATE_DEVICE, there is no default IRQ routing.
    /// We must explicitly route GSI numbers to GIC SPI pins via
    /// KVM_SET_GSI_ROUTING before register_irqfd will deliver interrupts.
    fn setup_gsi_routing(vm_fd: &VmFd) -> Result<()> {
        let irqs = [
            SERIAL_IRQ,
            SERIAL2_IRQ,
            VIRTIO_CONSOLE_IRQ,
            VIRTIO_BLK_IRQ,
            VIRTIO_NET_IRQ,
        ];
        let mut routing = KvmIrqRouting::new(irqs.len()).context("create KvmIrqRouting")?;
        for (i, &irq) in irqs.iter().enumerate() {
            routing.as_mut_slice()[i] = kvm_irq_routing_entry {
                gsi: irq,
                type_: KVM_IRQ_ROUTING_IRQCHIP,
                flags: 0,
                pad: 0,
                u: kvm_irq_routing_entry__bindgen_ty_1 {
                    irqchip: kvm_irq_routing_irqchip {
                        irqchip: 0,    // GIC device index
                        pin: irq - 32, // SPI pin (0-based); KVM adds 32 to get intid
                    },
                },
            };
        }
        // KVM_SET_GSI_ROUTING allocates a kernel-side routing table
        // (kfree_rcu replaces the old one); ENOMEM under host
        // pressure is transient.
        vm_fd.set_gsi_routing(&routing).map_err(|e| {
            crate::vmm::map_transient_to_contention(e, "set GSI routing for serial IRQs")
        })?;
        Ok(())
    }

    /// Initialise PMUv3 emulation on each vcpu.
    ///
    /// kvm_arm_pmu_v3_set_attr (arch/arm64/kvm/pmu-emul.c) requires the
    /// IRQ to be configured before INIT when the irqchip is in-kernel.
    /// Calling order:
    ///   1. KVM_ARM_VCPU_PMU_V3_IRQ — programs vcpu->arch.pmu.irq_num
    ///   2. KVM_ARM_VCPU_PMU_V3_INIT — checks irq is initialised, marks
    ///      pmu.created = true (further attr writes return -EBUSY).
    /// PMU_INTID is a PPI in the global intid namespace (16..32), so
    /// the same value is used for every vcpu per pmu_irq_is_valid.
    fn init_pmuv3(vcpus: &[VcpuFd]) -> Result<()> {
        for (cpu_id, vcpu) in vcpus.iter().enumerate() {
            let irq: u32 = PMU_INTID;
            let irq_attr = kvm_device_attr {
                group: KVM_ARM_VCPU_PMU_V3_CTRL,
                attr: KVM_ARM_VCPU_PMU_V3_IRQ as u64,
                addr: &irq as *const u32 as u64,
                flags: 0,
            };
            vcpu.set_device_attr(&irq_attr)
                .with_context(|| format!("set PMU IRQ on vcpu {cpu_id}"))?;

            let init_attr = kvm_device_attr {
                group: KVM_ARM_VCPU_PMU_V3_CTRL,
                attr: KVM_ARM_VCPU_PMU_V3_INIT as u64,
                addr: 0,
                flags: 0,
            };
            vcpu.set_device_attr(&init_attr)
                .with_context(|| format!("init PMU on vcpu {cpu_id}"))?;
        }
        Ok(())
    }
}

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

    #[test]
    fn create_vm_basic() {
        let topo = Topology {
            llcs: 1,
            cores_per_llc: 2,
            threads_per_core: 1,
            numa_nodes: 1,
            nodes: None,
            distances: None,
        };
        let vm = KtstrKvm::new(topo, 128, false);
        assert!(vm.is_ok(), "VM creation failed: {:?}", vm.err());
        let vm = vm.unwrap();
        assert_eq!(vm.vcpus.len(), 2);
    }

    #[test]
    fn create_vm_multi_llc() {
        let topo = Topology {
            llcs: 2,
            cores_per_llc: 2,
            threads_per_core: 2,
            numa_nodes: 1,
            nodes: None,
            distances: None,
        };
        let vm = KtstrKvm::new(topo, 256, false);
        assert!(vm.is_ok(), "multi-LLC VM creation failed: {:?}", vm.err());
        let vm = vm.unwrap();
        assert_eq!(vm.vcpus.len(), 8);
    }

    #[test]
    fn create_vm_single_cpu() {
        let topo = Topology {
            llcs: 1,
            cores_per_llc: 1,
            threads_per_core: 1,
            numa_nodes: 1,
            nodes: None,
            distances: None,
        };
        let vm = KtstrKvm::new(topo, 64, false);
        assert!(vm.is_ok());
        assert_eq!(vm.unwrap().vcpus.len(), 1);
    }

    #[test]
    fn memory_size_correct() {
        use vm_memory::GuestMemoryRegion;
        let topo = Topology {
            llcs: 1,
            cores_per_llc: 1,
            threads_per_core: 1,
            numa_nodes: 1,
            nodes: None,
            distances: None,
        };
        let vm = KtstrKvm::new(topo, 256, false).unwrap();
        let total: u64 = vm.guest_mem.iter().map(|r| r.len()).sum();
        assert_eq!(total, 256 << 20);
    }

    #[test]
    fn memory_starts_at_dram() {
        use vm_memory::GuestMemoryRegion;
        let topo = Topology {
            llcs: 1,
            cores_per_llc: 1,
            threads_per_core: 1,
            numa_nodes: 1,
            nodes: None,
            distances: None,
        };
        let vm = KtstrKvm::new(topo, 64, false).unwrap();
        let region = vm.guest_mem.iter().next().unwrap();
        assert_eq!(
            region.start_addr(),
            GuestAddress(DRAM_START),
            "guest memory must start at DRAM_START"
        );
    }

    #[test]
    fn immediate_exit_cap_detected() {
        let topo = Topology {
            llcs: 1,
            cores_per_llc: 1,
            threads_per_core: 1,
            numa_nodes: 1,
            nodes: None,
            distances: None,
        };
        let vm = KtstrKvm::new(topo, 64, false).unwrap();
        assert!(vm.has_immediate_exit);
    }

    #[test]
    fn gic_redist_does_not_overlap_dram() {
        // Maximum vCPUs that fit: (DRAM_START - GIC_REDIST_BASE) / GIC_REDIST_SIZE_PER_CPU
        let max_cpus = (DRAM_START - GIC_REDIST_BASE) / GIC_REDIST_SIZE_PER_CPU;
        assert!(
            max_cpus >= 128,
            "layout should support at least 128 vCPUs, got {max_cpus}"
        );
    }

    #[test]
    fn devices_below_dram() {
        const { assert!(GIC_DIST_BASE < DRAM_START) };
        const { assert!(GIC_REDIST_BASE < DRAM_START) };
        const { assert!(SERIAL_MMIO_BASE < DRAM_START) };
        const { assert!(SERIAL2_MMIO_BASE < DRAM_START) };
        const { assert!(VIRTIO_CONSOLE_MMIO_BASE < DRAM_START) };
        const {
            assert!(
                VIRTIO_CONSOLE_MMIO_BASE + crate::vmm::virtio_console::VIRTIO_MMIO_SIZE
                    <= DRAM_START
            )
        };
        const { assert!(VIRTIO_BLK_MMIO_BASE < DRAM_START) };
        const { assert!(VIRTIO_BLK_MMIO_BASE + crate::vmm::virtio_blk::VIRTIO_MMIO_SIZE <= DRAM_START) };
        const { assert!(VIRTIO_NET_MMIO_BASE < DRAM_START) };
        const { assert!(VIRTIO_NET_MMIO_BASE + crate::vmm::virtio_net::VIRTIO_MMIO_SIZE <= DRAM_START) };
    }

    /// PMU_PPI must reside in the GIC PPI namespace (0..15). Values
    /// outside that range would be rejected by the kernel's
    /// pmu_irq_is_valid (`arch/arm64/kvm/pmu-emul.c`), which gates the
    /// IRQ on `irq_is_ppi(irq)` (`include/kvm/arm_vgic.h` —
    /// `VGIC_NR_SGIS <= irq < VGIC_NR_PRIVATE_IRQS`, i.e. 16..32 in
    /// the global intid namespace, equivalently 0..15 in the FDT
    /// per-CPU PPI namespace).
    #[test]
    fn pmu_ppi_in_ppi_namespace() {
        // GIC PPIs occupy intids 16..32; PMU_PPI is the per-CPU
        // PPI form (0..15) used in the FDT cell.
        const { assert!(PMU_PPI < 16) };
    }

    /// PMU_INTID is the global-intid form KVM_ARM_VCPU_PMU_V3_IRQ
    /// expects. The kernel's pmu_irq_is_valid takes the global intid
    /// and runs `irq_is_ppi(irq)` which checks `16 <= irq < 32`. The
    /// const constraint here pins the namespace mapping in lockstep
    /// with the kernel's expected range — a regression that flipped
    /// PMU_INTID to e.g. PMU_PPI alone (no offset) or PMU_PPI + 32
    /// (SPI namespace) would surface here at compile time, before the
    /// per-vCPU `set_device_attr` ioctl returns -EINVAL.
    #[test]
    fn pmu_intid_in_ppi_intid_range() {
        const { assert!(PMU_INTID >= 16) };
        const { assert!(PMU_INTID < 32) };
    }

    /// PMU_INTID == PMU_PPI + VGIC_NR_SGIS. VGIC_NR_SGIS is 16 on
    /// arm64 (`include/kvm/arm_vgic.h`); a regression that flipped
    /// either constant out of step would surface as the kernel
    /// rejecting the IRQ via pmu_irq_is_valid before the second
    /// PMU_V3_INIT attr write lands.
    #[test]
    fn pmu_intid_offset_from_ppi() {
        const { assert!(PMU_INTID == PMU_PPI + 16) };
    }
}