diff --git a/pcid/src/driver_interface/irq_helpers.rs b/pcid/src/driver_interface/irq_helpers.rs
index 58d252be7a..5d380dba79 100644
--- a/pcid/src/driver_interface/irq_helpers.rs
+++ b/pcid/src/driver_interface/irq_helpers.rs
@@ -3,25 +3,45 @@
 //! This module allows easy handling of the `irq:` scheme, and allocating interrupt vectors for use
 //! by INTx#, MSI, or MSI-X.
 
+use std::convert::TryFrom;
 use std::fs::{self, File};
 use std::io::{self, prelude::*};
 use std::num::NonZeroU8;
 use std::ops;
 
 /// Read the local APIC ID of the bootstrap processor.
-pub fn read_bsp_apic_id() -> io::Result<u32> {
+pub fn read_bsp_apic_id() -> io::Result<usize> {
     let mut buffer = [0u8; 8];
 
     let mut file = File::open("irq:bsp")?;
     let bytes_read = file.read(&mut buffer)?;
 
-    Ok(if bytes_read == 8 {
-        u64::from_le_bytes(buffer) as u32
+    (if bytes_read == 8 {
+        usize::try_from(u64::from_le_bytes(buffer))
     } else if bytes_read == 4 {
-        u32::from_le_bytes([buffer[0], buffer[1], buffer[2], buffer[3]])
+        usize::try_from(u32::from_le_bytes([buffer[0], buffer[1], buffer[2], buffer[3]]))
     } else {
         panic!("`irq:` scheme responded with {} bytes, expected {}", bytes_read, std::mem::size_of::<usize>());
-    })
+    }).or(Err(io::Error::new(io::ErrorKind::InvalidData, "bad BSP int size")))
+}
+
+// TODO: Perhaps read the MADT instead?
+/// Obtains an interator over all of the visible CPU ids, for use in IRQ allocation and MSI
+/// capability structs or MSI-X tables.
+pub fn cpu_ids() -> io::Result<impl Iterator<Item = io::Result<usize>> + 'static> {
+    Ok(fs::read_dir("irq:")?
+        .filter_map(|entry| -> Option<io::Result<_>> { match entry {
+            Ok(e) => {
+                let path = e.path();
+                let file_name = path.file_name()?.to_str()?;
+                // the file name should be in the format `cpu-<CPU ID>`
+                if ! file_name.starts_with("cpu-") {
+                    return None;
+                }
+                u8::from_str_radix(&file_name[4..], 16).map(usize::from).map(Ok).ok()
+            }
+            Err(e) => Some(Err(e)),
+        } }))
 }
 
 /// Allocate multiple interrupt vectors, from the IDT of the bootstrap processor, returning the
@@ -41,10 +61,13 @@ pub fn read_bsp_apic_id() -> io::Result<u32> {
 /// individually allocated vectors that might be spread out, even on multiple CPUs. Thus, multiple
 /// invocations with alignment 1 and count 1 are totally acceptable, although allocating in bulk
 /// minimizes the initialization overhead, even though it's negligible.
-pub fn allocate_aligned_interrupt_vectors(alignment: NonZeroU8, count: u8) -> io::Result<Option<(u8, Vec<File>)>> {
+///
+/// Every interrupt vector will be allocated in the same CPU's IDT, as specified by `cpu_id`.
+pub fn allocate_aligned_interrupt_vectors(cpu_id: usize, alignment: NonZeroU8, count: u8) -> io::Result<Option<(u8, Vec<File>)>> {
+    let cpu_id = u8::try_from(cpu_id).expect("usize cpu ids not implemented yet");
     if count == 0 { return Ok(None) }
 
-    let available_irqs = fs::read_dir("irq:")?;
+    let available_irqs = fs::read_dir(format!("irq:{:02x}", cpu_id))?;
     let mut available_irq_numbers = available_irqs.filter_map(|entry| -> Option<io::Result<_>> {
         let entry = match entry {
             Ok(e) => e,
@@ -63,8 +86,6 @@ pub fn allocate_aligned_interrupt_vectors(alignment: NonZeroU8, count: u8) -> io
             None => return None,
         };
 
-        // note that there might be future subdirectories in the IRQ scheme, such as `cpu-<APIC
-        // ID>/<IRQ>`, thus no error but just None
         match path_str.parse::<u8>() {
             Ok(p) => Some(Ok(p)),
             Err(_) => None,
@@ -119,15 +140,15 @@ pub fn allocate_aligned_interrupt_vectors(alignment: NonZeroU8, count: u8) -> io
 
 /// Allocate at most `count` interrupt vectors, which can start at any offset. Unless MSI is used
 /// and an entire aligned range of vectors is needed, this function should be used.
-pub fn allocate_interrupt_vectors(count: u8) -> io::Result<Option<(u8, Vec<File>)>> {
-    allocate_aligned_interrupt_vectors(NonZeroU8::new(1).unwrap(), count)
+pub fn allocate_interrupt_vectors(cpu_id: usize, count: u8) -> io::Result<Option<(u8, Vec<File>)>> {
+    allocate_aligned_interrupt_vectors(cpu_id, NonZeroU8::new(1).unwrap(), count)
 }
 
 /// Allocate a single interrupt vector, returning both the vector number (starting from 32 up to
 /// 254), and its IRQ handle which is then reserved. Returns Ok(None) if allocation fails due to
 /// no available IRQs.
-pub fn allocate_single_interrupt_vector() -> io::Result<Option<(u8, File)>> {
-    let (base, mut files) = match allocate_interrupt_vectors(1) {
+pub fn allocate_single_interrupt_vector(cpu_id: usize) -> io::Result<Option<(u8, File)>> {
+    let (base, mut files) = match allocate_interrupt_vectors(cpu_id, 1) {
         Ok(Some((base, files))) => (base, files),
         Ok(None) => return Ok(None),
         Err(err) => return Err(err),
diff --git a/xhcid/src/main.rs b/xhcid/src/main.rs
index 8b9c38c026..adcad485f8 100644
--- a/xhcid/src/main.rs
+++ b/xhcid/src/main.rs
@@ -1,7 +1,7 @@
 #[macro_use]
 extern crate bitflags;
 
-use std::convert::TryInto;
+use std::convert::{TryFrom, TryInto};
 use std::fs::{self, File};
 use std::future::Future;
 use std::io::{self, Read, Write};
@@ -52,7 +52,7 @@ fn main() {
         Ok(logger) => match logger.with_stdout_mirror().enable() {
             Ok(_) => {
                 println!("xhcid: enabled logger");
-                log::set_max_level(log::LevelFilter::Debug);
+                log::set_max_level(log::LevelFilter::Trace);
             }
             Err(error) => eprintln!("xhcid: failed to set default logger: {}", error),
         }
@@ -102,9 +102,10 @@ fn main() {
         // pcid_interface, so that this can be shared between nvmed, xhcid, ixgebd, etc..
 
         let destination_id = read_bsp_apic_id().expect("xhcid: failed to read BSP apic id");
-        let msg_addr = x86_64_msix::message_address(destination_id as u8, false, false, 0b00);
+        let lapic_id = u8::try_from(destination_id).expect("CPU id didn't fit inside u8");
+        let msg_addr = x86_64_msix::message_address(lapic_id, false, false, 0b00);
 
-        let (vector, interrupt_handle) = allocate_single_interrupt_vector().expect("xhcid: failed to allocate interrupt vector").expect("xhcid: no interrupt vectors left");
+        let (vector, interrupt_handle) = allocate_single_interrupt_vector(destination_id).expect("xhcid: failed to allocate interrupt vector").expect("xhcid: no interrupt vectors left");
         let msg_data = x86_64_msix::message_data_edge_triggered(DeliveryMode::Fixed, vector);
 
         let set_feature_info = MsiSetFeatureInfo {
@@ -161,11 +162,12 @@ fn main() {
             let table_entry_pointer = info.table_entry_pointer(k);
 
             let destination_id = read_bsp_apic_id().expect("xhcid: failed to read BSP apic id");
+            let lapic_id = u8::try_from(destination_id).expect("xhcid: CPU id couldn't fit inside u8");
             let rh = false;
             let dm = false;
-            let addr = x86_64_msix::message_address(destination_id.try_into().expect("xhcid: BSP apic id couldn't fit u8"), rh, dm, 0b00);
+            let addr = x86_64_msix::message_address(lapic_id, rh, dm, 0b00);
 
-            let (vector, interrupt_handle) = allocate_single_interrupt_vector().expect("xhcid: failed to allocate interrupt vector").expect("xhcid: no interrupt vectors left");
+            let (vector, interrupt_handle) = allocate_single_interrupt_vector(destination_id).expect("xhcid: failed to allocate interrupt vector").expect("xhcid: no interrupt vectors left");
             let msg_data = x86_64_msix::message_data_edge_triggered(DeliveryMode::Fixed, vector);
 
             table_entry_pointer.addr_lo.write(addr);