UserspaceEmulator: Implement a proper VM allocator

This patch brings Kernel::RangeAllocator to UserspaceEmulator in a
slightly simplified form.

It supports the basic three allocation types needed by virt$mmap():
allocate_anywhere, allocate_specific, and allocate_randomized.

Porting virt$mmap() and virt$munmap() to use the allocator makes
UE work correctly once again. :^)

Userland/DevTools/UserspaceEmulator/RangeAllocator.cpp

@@ -0,0 +1,207 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "RangeAllocator.h"
+#include <AK/BinarySearch.h>
+#include <AK/Checked.h>
+#include <AK/QuickSort.h>
+#include <AK/Random.h>
+
+#define VM_GUARD_PAGES
+#define PAGE_MASK ((FlatPtr)0xfffff000u)
+
+namespace UserspaceEmulator {
+
+RangeAllocator::RangeAllocator()
+    : m_total_range({}, 0)
+{
+}
+
+void RangeAllocator::initialize_with_range(VirtualAddress base, size_t size)
+{
+    m_total_range = { base, size };
+    m_available_ranges.append({ base, size });
+}
+
+RangeAllocator::~RangeAllocator()
+{
+}
+
+void RangeAllocator::dump() const
+{
+    dbgln("RangeAllocator({})", this);
+    for (auto& range : m_available_ranges) {
+        dbgln("    {:x} -> {:x}", range.base().get(), range.end().get() - 1);
+    }
+}
+
+void RangeAllocator::carve_at_index(int index, const Range& range)
+{
+    auto remaining_parts = m_available_ranges[index].carve(range);
+    ASSERT(remaining_parts.size() >= 1);
+    ASSERT(m_total_range.contains(remaining_parts[0]));
+    m_available_ranges[index] = remaining_parts[0];
+    if (remaining_parts.size() == 2) {
+        ASSERT(m_total_range.contains(remaining_parts[1]));
+        m_available_ranges.insert(index + 1, move(remaining_parts[1]));
+    }
+}
+
+Optional<Range> RangeAllocator::allocate_randomized(size_t size, size_t alignment)
+{
+    if (!size)
+        return {};
+
+    ASSERT((size % PAGE_SIZE) == 0);
+    ASSERT((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 { AK::get_random<FlatPtr>() };
+        random_address.mask(PAGE_MASK);
+
+        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<Range> RangeAllocator::allocate_anywhere(size_t size, size_t alignment)
+{
+    if (!size)
+        return {};
+
+    ASSERT((size % PAGE_SIZE) == 0);
+    ASSERT((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 {};
+
+    for (size_t i = 0; i < m_available_ranges.size(); ++i) {
+        auto& available_range = m_available_ranges[i];
+        // 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);
+
+        Range allocated_range(VirtualAddress(aligned_base), size);
+        ASSERT(m_total_range.contains(allocated_range));
+
+        if (available_range == allocated_range) {
+            m_available_ranges.remove(i);
+            return allocated_range;
+        }
+        carve_at_index(i, allocated_range);
+        return allocated_range;
+    }
+    klog() << "RangeAllocator: Failed to allocate anywhere: " << size << ", " << alignment;
+    return {};
+}
+
+Optional<Range> RangeAllocator::allocate_specific(VirtualAddress base, size_t size)
+{
+    if (!size)
+        return {};
+
+    ASSERT(base.is_page_aligned());
+    ASSERT((size % PAGE_SIZE) == 0);
+
+    Range allocated_range(base, size);
+    for (size_t i = 0; i < m_available_ranges.size(); ++i) {
+        auto& available_range = m_available_ranges[i];
+        ASSERT(m_total_range.contains(allocated_range));
+        if (!available_range.contains(base, size))
+            continue;
+        if (available_range == allocated_range) {
+            m_available_ranges.remove(i);
+            return allocated_range;
+        }
+        carve_at_index(i, allocated_range);
+        return allocated_range;
+    }
+    return {};
+}
+
+void RangeAllocator::deallocate(const Range& range)
+{
+    ASSERT(m_total_range.contains(range));
+    ASSERT(range.size());
+    ASSERT((range.size() % PAGE_SIZE) == 0);
+    ASSERT(range.base() < range.end());
+    ASSERT(!m_available_ranges.is_empty());
+
+    size_t nearby_index = 0;
+    auto* existing_range = binary_search(
+        m_available_ranges.span(),
+        range,
+        &nearby_index,
+        [](auto& a, auto& b) { return a.base().get() - b.end().get(); });
+
+    size_t inserted_index = 0;
+    if (existing_range) {
+        existing_range->m_size += range.size();
+        inserted_index = nearby_index;
+    } else {
+        m_available_ranges.insert_before_matching(
+            Range(range), [&](auto& entry) {
+                return entry.base() >= range.end();
+            },
+            nearby_index, &inserted_index);
+    }
+
+    if (inserted_index < (m_available_ranges.size() - 1)) {
+        // We already merged with previous. Try to merge with next.
+        auto& inserted_range = m_available_ranges[inserted_index];
+        auto& next_range = m_available_ranges[inserted_index + 1];
+        if (inserted_range.end() == next_range.base()) {
+            inserted_range.m_size += next_range.size();
+            m_available_ranges.remove(inserted_index + 1);
+            return;
+        }
+    }
+}
+
+}