fix: kernel concurrency, interrupt context, and user VA safety

kernel/src/Hal/IDT.cpp

@@ -13,6 +13,7 @@
 #include <Memory/PageFrameAllocator.hpp>
 #include <Sched/Scheduler.hpp>
 #include <Sched/CrashReport.hpp>
+#include <Hal/SmpBoot.hpp>
 #include <Timekeeping/ApicTimer.hpp>
 
 namespace Hal {
@@ -93,6 +94,14 @@ namespace Hal {
         // If the fault originated in user-mode (ring 3), kill the process
         // instead of panicking the entire system.
         if (fromUser && Sched::GetCurrentPid() >= 0) {
+            // Interrupt gates arrive with IF clear. Full process teardown can
+            // wait on device completions, sibling CPUs, and wall-clock-bounded
+            // recovery paths, so leaving IF clear here can stop the BSP clock
+            // and its local device IRQs indefinitely. GS is already the kernel
+            // per-CPU base, and timer/IPI scheduling refuses to switch away
+            // from a ring-0 frame, so nested hardware IRQs are safe now.
+            asm volatile("sti" ::: "memory");
+
             auto* proc = Sched::GetCurrentProcessPtr();
             auto* regs = GetExceptionRegs(i, frame);
             Kt::KernelLogStream(Kt::ERROR, "Exception")
@@ -183,6 +192,7 @@ namespace Hal {
     {
         bool fromUser = (frame->CS & 3) == 3;
         if (fromUser) asm volatile("swapgs");
+        auto* cpu = Smp::TryGetCurrentCpuData();
 
         uint64_t cr2;
         asm volatile("mov %%cr2, %0" : "=r"(cr2));
@@ -190,7 +200,8 @@ namespace Hal {
         // Bit 0 of the error code: 0 = non-present page. Covers both user
         // pushes past the mapped stack and kernel accesses to not-yet-grown
         // user stack buffers passed into syscalls.
-        if ((errorCode & 1) == 0 && Sched::GetCurrentPid() >= 0
+        if ((errorCode & 1) == 0 && cpu != nullptr && cpu->currentSlot >= 0
+            && Sched::GetCurrentPid() >= 0
             && Sched::TryGrowUserStack(cr2)) {
             if (fromUser) asm volatile("swapgs");
             return;