Kernel/x86: Re-enable interrupts ASAP when handling page faults

As soon as we've saved CR2 (the faulting address), we can re-enable
interrupt processing. This should make the kernel more responsive under
heavy fault loads.

Kernel/Arch/x86/common/Interrupts.cpp

@@ -254,8 +254,12 @@ void page_fault_handler(TrapFrame* trap)
 {
     clac();
 
-    auto& regs = *trap->regs;
+    // NOTE: Once we've extracted the faulting address from CR2,
+    //       we can re-enable interrupts.
     auto fault_address = read_cr2();
+    sti();
+
+    auto& regs = *trap->regs;
 
     if constexpr (PAGE_FAULT_DEBUG) {
         u32 fault_page_directory = read_cr3();

Kernel/Memory/AnonymousVMObject.cpp

@@ -317,7 +317,6 @@ size_t AnonymousVMObject::cow_pages() const
 
 PageFaultResponse AnonymousVMObject::handle_cow_fault(size_t page_index, VirtualAddress vaddr)
 {
-    VERIFY_INTERRUPTS_DISABLED();
     SpinlockLocker lock(m_lock);
 
     if (is_volatile()) {

Kernel/Memory/MemoryManager.cpp

@@ -715,8 +715,6 @@ Region* MemoryManager::find_region_from_vaddr(VirtualAddress vaddr)
 
 PageFaultResponse MemoryManager::handle_page_fault(PageFault const& fault)
 {
-    VERIFY_INTERRUPTS_DISABLED();
-
     auto faulted_in_range = [&fault](auto const* start, auto const* end) {
         return fault.vaddr() >= VirtualAddress { start } && fault.vaddr() < VirtualAddress { end };
     };

Kernel/Memory/Region.cpp

@@ -402,7 +402,6 @@ PageFaultResponse Region::handle_fault(PageFault const& fault)
 
 PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
 {
-    VERIFY_INTERRUPTS_DISABLED();
     VERIFY(vmobject().is_anonymous());
 
     SpinlockLocker locker(vmobject().m_lock);
@@ -444,7 +443,6 @@ PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
 
 PageFaultResponse Region::handle_cow_fault(size_t page_index_in_region)
 {
-    VERIFY_INTERRUPTS_DISABLED();
     auto current_thread = Thread::current();
     if (current_thread)
         current_thread->did_cow_fault();
@@ -461,7 +459,6 @@ PageFaultResponse Region::handle_cow_fault(size_t page_index_in_region)
 
 PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
 {
-    VERIFY_INTERRUPTS_DISABLED();
     VERIFY(vmobject().is_inode());
     VERIFY(!s_mm_lock.is_locked_by_current_processor());
     VERIFY(!g_scheduler_lock.is_locked_by_current_processor());