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/*
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include "RangeAllocator.h"
#include <AK/BinarySearch.h>
#include <AK/Checked.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 });
}
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);
VERIFY(remaining_parts.size() >= 1);
VERIFY(m_total_range.contains(remaining_parts[0]));
m_available_ranges[index] = remaining_parts[0];
if (remaining_parts.size() == 2) {
VERIFY(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 {};
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_random<FlatPtr>(), 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<Range> RangeAllocator::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 {};
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);
VERIFY(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;
}
dbgln("RangeAllocator: Failed to allocate anywhere: size={}, alignment={}", size, alignment);
return {};
}
Optional<Range> RangeAllocator::allocate_specific(VirtualAddress base, size_t size)
{
if (!size)
return {};
VERIFY(base.is_page_aligned());
VERIFY((size % PAGE_SIZE) == 0);
Range allocated_range(base, size);
if (!m_total_range.contains(allocated_range)) {
dbgln("Unallocatable mmap request?! {:p}+{:p}", base.get(), size);
return {};
}
for (size_t i = 0; i < m_available_ranges.size(); ++i) {
auto& available_range = m_available_ranges[i];
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)
{
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());
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;
}
}
}
}
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