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/*
* 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());
}
}
}
}
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