LibWeb: Make VM allocation atomic for kernel regions

Instead of first allocating the VM range, and then inserting a region
with that range into the MM region tree, we now do both things in a
single atomic operation:

    - RegionTree::place_anywhere(Region&, size, alignment)
    - RegionTree::place_specifically(Region&, address, size)

To reduce the number of things we do while locking the region tree,
we also require callers to provide a constructed Region object.

1 files changed, 8 insertions, 13 deletions

diff --git a/Kernel/Interrupts/APIC.cpp b/Kernel/Interrupts/APIC.cpp
index e54437c1fd..75bf6cecfd 100644
--- a/Kernel/Interrupts/APIC.cpp
+++ b/Kernel/Interrupts/APIC.cpp
@@ -319,19 +319,14 @@ UNMAP_AFTER_INIT bool APIC::init_bsp()
     return true;
 }
 
-UNMAP_AFTER_INIT static NonnullOwnPtr<Memory::Region> create_identity_mapped_region(PhysicalAddress paddr, size_t size)
+UNMAP_AFTER_INIT static ErrorOr<NonnullOwnPtr<Memory::Region>> create_identity_mapped_region(PhysicalAddress paddr, size_t size)
 {
-    auto maybe_vmobject = Memory::AnonymousVMObject::try_create_for_physical_range(paddr, size);
-    // FIXME: Would be nice to be able to return a ErrorOr from here.
-    VERIFY(!maybe_vmobject.is_error());
-
-    auto region_or_error = MM.allocate_kernel_region_with_vmobject(
-        Memory::VirtualRange { VirtualAddress { static_cast<FlatPtr>(paddr.get()) }, size },
-        maybe_vmobject.release_value(),
-        {},
-        Memory::Region::Access::ReadWriteExecute);
-    VERIFY(!region_or_error.is_error());
-    return region_or_error.release_value();
+    auto vmobject = TRY(Memory::AnonymousVMObject::try_create_for_physical_range(paddr, size));
+    auto region = TRY(Memory::Region::create_unplaced(move(vmobject), 0, {}, Memory::Region::Access::ReadWriteExecute));
+    Memory::VirtualRange range { VirtualAddress { paddr.get() }, size };
+    TRY(MM.region_tree().place_specifically(*region, range));
+    TRY(region->map(MM.kernel_page_directory()));
+    return region;
 }
 
 UNMAP_AFTER_INIT void APIC::setup_ap_boot_environment()
@@ -347,7 +342,7 @@ UNMAP_AFTER_INIT void APIC::setup_ap_boot_environment()
     constexpr u64 apic_startup_region_base = 0x8000;
     auto apic_startup_region_size = Memory::page_round_up(apic_ap_start_size + (2 * aps_to_enable * sizeof(FlatPtr))).release_value_but_fixme_should_propagate_errors();
     VERIFY(apic_startup_region_size < USER_RANGE_BASE);
-    auto apic_startup_region = create_identity_mapped_region(PhysicalAddress(apic_startup_region_base), apic_startup_region_size);
+    auto apic_startup_region = MUST(create_identity_mapped_region(PhysicalAddress(apic_startup_region_base), apic_startup_region_size));
     u8* apic_startup_region_ptr = apic_startup_region->vaddr().as_ptr();
     memcpy(apic_startup_region_ptr, reinterpret_cast<void const*>(apic_ap_start), apic_ap_start_size);