feat: support for USB mass storage devices, hotplugging

kernel/src/Timekeeping/ApicTimer.cpp

@@ -105,9 +105,6 @@ namespace Timekeeping {
             if (Drivers::Net::E1000E::RequiresPolling()) {
                 Drivers::Net::E1000E::Poll();
             }
-            if (Drivers::USB::Xhci::HasDeferredWork()) {
-                Drivers::USB::Xhci::ProcessDeferredWork();
-            }
             Drivers::USB::HidKeyboard::Tick();
         }
 
@@ -246,6 +243,15 @@ namespace Timekeeping {
 
     void IdleOnce(bool hasMwait, volatile uint64_t* monitorAddr) {
         auto* cpu = Smp::GetCurrentCpuData();
+
+        // Drain USB hot-plug deferred work from any idle core, not just the BSP.
+        // ProcessDeferredWork uses an atomic CAS so only one core runs it at a
+        // time; the rest return immediately. This keeps hot-plug latency bounded
+        // by *any* core's idle gap instead of being pinned to BSP idle.
+        if (Drivers::USB::Xhci::HasDeferredWork()) {
+            Drivers::USB::Xhci::ProcessDeferredWork();
+        }
+
         if (cpu == nullptr || cpu->cpuIndex != 0 || !g_schedEnabled || g_ticksPerMs == 0) {
             Hal::CpuIdle::Wait(BSP_TICK_INTERVAL_MS, hasMwait, monitorAddr);
             return;