Kernel: Rename Range => VirtualRange

...and also RangeAllocator => VirtualRangeAllocator.

This clarifies that the ranges we're dealing with are *virtual* memory
ranges and not anything else.

Kernel/Memory/VirtualRangeAllocator.cpp

@@ -0,0 +1,194 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Checked.h>
+#include <Kernel/Memory/VirtualRangeAllocator.h>
+#include <Kernel/Random.h>
+
+#define VM_GUARD_PAGES
+
+namespace Kernel::Memory {
+
+VirtualRangeAllocator::VirtualRangeAllocator()
+    : m_total_range({}, 0)
+{
+}
+
+void VirtualRangeAllocator::initialize_with_range(VirtualAddress base, size_t size)
+{
+    m_total_range = { base, size };
+    m_available_ranges.insert(base.get(), VirtualRange { base, size });
+}
+
+void VirtualRangeAllocator::initialize_from_parent(VirtualRangeAllocator const& parent_allocator)
+{
+    ScopedSpinLock lock(parent_allocator.m_lock);
+    m_total_range = parent_allocator.m_total_range;
+    m_available_ranges.clear();
+    for (auto it = parent_allocator.m_available_ranges.begin(); !it.is_end(); ++it) {
+        m_available_ranges.insert(it.key(), *it);
+    }
+}
+
+void VirtualRangeAllocator::dump() const
+{
+    VERIFY(m_lock.is_locked());
+    dbgln("VirtualRangeAllocator({})", this);
+    for (auto& range : m_available_ranges) {
+        dbgln("    {:x} -> {:x}", range.base().get(), range.end().get() - 1);
+    }
+}
+
+void VirtualRangeAllocator::carve_at_iterator(auto& it, VirtualRange const& range)
+{
+    VERIFY(m_lock.is_locked());
+    auto remaining_parts = (*it).carve(range);
+    VERIFY(remaining_parts.size() >= 1);
+    VERIFY(m_total_range.contains(remaining_parts[0]));
+    m_available_ranges.remove(it.key());
+    m_available_ranges.insert(remaining_parts[0].base().get(), remaining_parts[0]);
+    if (remaining_parts.size() == 2) {
+        VERIFY(m_total_range.contains(remaining_parts[1]));
+        m_available_ranges.insert(remaining_parts[1].base().get(), remaining_parts[1]);
+    }
+}
+
+Optional<VirtualRange> VirtualRangeAllocator::allocate_randomized(size_t size, size_t alignment)
+{
+    if (!size)
+        return {};
+
+    VERIFY((size % PAGE_SIZE) == 0);
+    VERIFY((alignment % PAGE_SIZE) == 0);
+
+    // FIXME: I'm sure there's a smarter way to do this.
+    static constexpr size_t maximum_randomization_attempts = 1000;
+    for (size_t i = 0; i < maximum_randomization_attempts; ++i) {
+        VirtualAddress random_address { round_up_to_power_of_two(get_fast_random<FlatPtr>() % m_total_range.end().get(), alignment) };
+
+        if (!m_total_range.contains(random_address, size))
+            continue;
+
+        auto range = allocate_specific(random_address, size);
+        if (range.has_value())
+            return range;
+    }
+
+    return allocate_anywhere(size, alignment);
+}
+
+Optional<VirtualRange> VirtualRangeAllocator::allocate_anywhere(size_t size, size_t alignment)
+{
+    if (!size)
+        return {};
+
+    VERIFY((size % PAGE_SIZE) == 0);
+    VERIFY((alignment % PAGE_SIZE) == 0);
+
+#ifdef VM_GUARD_PAGES
+    // NOTE: We pad VM allocations with a guard page on each side.
+    if (Checked<size_t>::addition_would_overflow(size, PAGE_SIZE * 2))
+        return {};
+
+    size_t effective_size = size + PAGE_SIZE * 2;
+    size_t offset_from_effective_base = PAGE_SIZE;
+#else
+    size_t effective_size = size;
+    size_t offset_from_effective_base = 0;
+#endif
+
+    if (Checked<size_t>::addition_would_overflow(effective_size, alignment))
+        return {};
+
+    ScopedSpinLock lock(m_lock);
+
+    for (auto it = m_available_ranges.begin(); !it.is_end(); ++it) {
+        auto& available_range = *it;
+        // FIXME: This check is probably excluding some valid candidates when using a large alignment.
+        if (available_range.size() < (effective_size + alignment))
+            continue;
+
+        FlatPtr initial_base = available_range.base().offset(offset_from_effective_base).get();
+        FlatPtr aligned_base = round_up_to_power_of_two(initial_base, alignment);
+
+        VirtualRange const allocated_range(VirtualAddress(aligned_base), size);
+
+        VERIFY(m_total_range.contains(allocated_range));
+
+        if (available_range == allocated_range) {
+            m_available_ranges.remove(it.key());
+            return allocated_range;
+        }
+        carve_at_iterator(it, allocated_range);
+        return allocated_range;
+    }
+    dmesgln("VirtualRangeAllocator: Failed to allocate anywhere: size={}, alignment={}", size, alignment);
+    return {};
+}
+
+Optional<VirtualRange> VirtualRangeAllocator::allocate_specific(VirtualAddress base, size_t size)
+{
+    if (!size)
+        return {};
+
+    VERIFY(base.is_page_aligned());
+    VERIFY((size % PAGE_SIZE) == 0);
+
+    VirtualRange const allocated_range(base, size);
+    if (!m_total_range.contains(allocated_range)) {
+        return {};
+    }
+
+    ScopedSpinLock lock(m_lock);
+    for (auto it = m_available_ranges.begin(); !it.is_end(); ++it) {
+        auto& available_range = *it;
+        if (!available_range.contains(base, size))
+            continue;
+        if (available_range == allocated_range) {
+            m_available_ranges.remove(it.key());
+            return allocated_range;
+        }
+        carve_at_iterator(it, allocated_range);
+        return allocated_range;
+    }
+    return {};
+}
+
+void VirtualRangeAllocator::deallocate(VirtualRange const& range)
+{
+    ScopedSpinLock lock(m_lock);
+    VERIFY(m_total_range.contains(range));
+    VERIFY(range.size());
+    VERIFY((range.size() % PAGE_SIZE) == 0);
+    VERIFY(range.base() < range.end());
+    VERIFY(!m_available_ranges.is_empty());
+
+    VirtualRange merged_range = range;
+
+    {
+        // Try merging with preceding range.
+        auto* preceding_range = m_available_ranges.find_largest_not_above(range.base().get());
+        if (preceding_range && preceding_range->end() == range.base()) {
+            preceding_range->m_size += range.size();
+            merged_range = *preceding_range;
+        } else {
+            m_available_ranges.insert(range.base().get(), range);
+        }
+    }
+
+    {
+        // Try merging with following range.
+        auto* following_range = m_available_ranges.find_largest_not_above(range.end().get());
+        if (following_range && merged_range.end() == following_range->base()) {
+            auto* existing_range = m_available_ranges.find_largest_not_above(range.base().get());
+            VERIFY(existing_range->base() == merged_range.base());
+            existing_range->m_size += following_range->size();
+            m_available_ranges.remove(following_range->base().get());
+        }
+    }
+}
+
+}