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Implement Multi-Level Range Table
A data structure that can represent the same value for a range of addresses (pages) is required for fast lookup in certain cases. This commit implements a near optimal data structure for mass insertion and O(1) lookup of range-based data, this is achieved using the host MMU and implementing multiple levels of atomicity for the ranges. It should be noted that the table is limited to two levels but can be extended to a variable amount of ranges in the future, it was determined that additional levels of ranges can be beneficial for performance depending on the specific use-case.
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PixelyIon
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app/src/main/cpp/skyline/common/range_table.h
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199
app/src/main/cpp/skyline/common/range_table.h
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// SPDX-License-Identifier: MPL-2.0
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// Copyright © 2022 Skyline Team and Contributors (https://github.com/skyline-emu/)
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#pragma once
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#include <sys/mman.h>
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#include "span.h"
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namespace skyline {
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/**
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* @brief A two-level range table implementation that utilizes kernel-backed demand paging, the multi-level aspect is to allow for a RangeType that applies to a large amount of ranges to be mapped at a lower granularity (L2) and go to a higher granuality (L1) as needed
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* @tparam RangeType The type of range to use for the range table entries, this must be a trivial type as it'll be returned filled with 0s when a range is unset
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* @tparam Size The size of the table in terms of units (not ranges unless L1Bits = 1), this represents size in bytes for a range table covering address space
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* @tparam L1Bits The size of an L1 range as a power of 2, this should be lower than L2 and will determine the minimum granularity of the table
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* @tparam L2Bits The size of an L2 range as a power of 2, this should be higher than L2 and will determine the maximum granularity of the table
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* @tparam EnablePointerAccess Whether or not to enable pointer access to the table, this is useful when host addresses are used as the key for the table
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* @note This class is **NOT** thread-safe, any access to the table must be protected by a mutex
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*/
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template<typename RangeType, size_t Size, size_t L1Bits, size_t L2Bits, bool EnablePointerAccess = false> requires std::is_trivial_v<RangeType>
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class RangeTable {
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private:
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static constexpr size_t L1Size{1 << L1Bits}, L1Entries{util::DivideCeil(Size, L1Size)};
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span<RangeType, L1Entries> level1Table; //!< The first level of the range table, this is the highest granularity of the table and contains only the range
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/**
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* @brief An entry in a range table level aside from the lowest level which directly holds the type, this has an associated range and a flag if the lookup should move to a higher granularity (and the corresponding lower level)
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*/
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struct alignas(8) RangeEntry {
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RangeType range; //!< The range associated with the entry, this is 0'd out if the entry is unset
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bool valid; //!< If the associated range is valid, the entry must not be accessed without checking validity first
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bool level1Set; //!< If to ignore this level and look in the next level table instead
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};
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static constexpr size_t L2Size{1 << L2Bits}, L2Entries{util::DivideCeil(Size, L2Size)}, L1inL2Count{L1Size / L2Size};
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span<RangeEntry, L2Entries> level2Table; //!< The second level of the range table, this is the lowest granularity of the table
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template<typename Type, size_t Amount>
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static span<Type, Amount> AllocateTable() {
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void *ptr{mmap(nullptr, Amount * sizeof(Type), PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, -1, 0)};
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if (ptr == MAP_FAILED)
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throw exception{"Failed to allocate 0x{:X} bytes of memory for range table: {}", Amount * sizeof(Type), strerror(errno)};
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return span<Type, Amount>(static_cast<Type *>(ptr), Amount);
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}
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public:
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RangeTable() : level1Table{AllocateTable<RangeType, L1Entries>()}, level2Table{AllocateTable<RangeEntry, L2Entries>()} {}
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RangeTable(const RangeTable &other) : level1Table{AllocateTable<RangeType, L1Entries>()}, level2Table{AllocateTable<RangeEntry, L2Entries>()} {
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level1Table.copy_from(other.level1Table);
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level2Table.copy_from(other.level2Table);
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}
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RangeTable &operator=(const RangeTable &other) {
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level1Table = AllocateTable<RangeType, L1Entries>();
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level2Table = AllocateTable<RangeEntry, L2Entries>();
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level1Table.copy_from(other.level1Table);
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level2Table.copy_from(other.level2Table);
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return *this;
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}
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RangeTable(RangeTable &&other) : level1Table{std::exchange(other.level1Table, nullptr)}, level2Table{std::exchange(other.level2Table, nullptr)} {}
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RangeTable &operator=(RangeTable &&other) {
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level1Table = std::exchange(other.level1Table, nullptr);
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level2Table = std::exchange(other.level2Table, nullptr);
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return *this;
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}
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~RangeTable() {
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if (level1Table.valid())
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munmap(level1Table.data(), level1Table.size_bytes());
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if (level2Table.valid())
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munmap(level2Table.data(), level2Table.size_bytes());
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}
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/**
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* @return A read-only reference to the range at the given index, this'll return a 0'd out range if the range is unset
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*/
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const RangeType &operator[](size_t index) const {
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auto &l2Entry{level2Table[index >> L2Bits]};
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if (l2Entry.valid)
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return l2Entry.range;
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return level1Table[index >> L1Bits];
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}
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/**
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* @brief Sets a single range at the specified index to the supplied value
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*/
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void Set(size_t index, RangeType range) {
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auto &l2Entry{level2Table[index >> L2Bits]};
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if (l2Entry.valid || l2Entry.level1Set) {
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if (l2Entry.range == range)
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return;
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l2Entry.valid = false;
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l2Entry.level1Set = true;
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size_t l1L2Start{(index >> L2Bits) << (L2Bits - L1Bits)};
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for (size_t i{l1L2Start}; i < l1L2Start + L1inL2Count; i++)
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level1Table[i] = l2Entry.range;
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level1Table[index >> L1Bits] = range;
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} else if (l2Entry.level1Set) {
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level1Table[index >> L1Bits] = range;
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} else {
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l2Entry.range = range;
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l2Entry.valid = true;
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l2Entry.level1Set = true;
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}
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}
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/**
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* @brief Sets a range of ranges between the start and end to the supplied value
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*/
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void Set(size_t start, size_t end, RangeType range) {
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size_t l2AlignedAddress{util::AlignUp(start, L2Size)};
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size_t l1StartPaddingStart{start >> L1Bits};
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size_t l1StartPaddingEnd{l2AlignedAddress >> L1Bits};
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if (l1StartPaddingStart != l1StartPaddingEnd) {
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auto &l2Entry{level2Table[start >> L2Bits]};
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if (l2Entry.valid) {
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l2Entry.valid = false;
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l2Entry.level1Set = true;
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size_t l1L2Start{(start >> L2Bits) << (L2Bits - L1Bits)};
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for (size_t i{l1L2Start}; i < l1StartPaddingStart; i++)
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level1Table[i] = l2Entry.range;
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for (size_t i{l1StartPaddingStart}; i < l1StartPaddingEnd; i++)
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level1Table[i] = range;
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} else if (!l2Entry.level1Set) {
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l2Entry.range = range;
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l2Entry.valid = true;
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l2Entry.level1Set = false;
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} else {
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for (size_t i{l1StartPaddingStart}; i < l1StartPaddingEnd; i++)
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level1Table[i] = range;
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}
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}
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size_t l2IndexStart{l2AlignedAddress >> L2Bits};
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size_t l2IndexEnd{end >> L2Bits};
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for (size_t i{l2IndexStart}; i < l2IndexEnd; i++) {
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auto &l2Entry{level2Table[i]};
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l2Entry.range = range;
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l2Entry.valid = true;
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l2Entry.level1Set = false;
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}
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size_t l1EndPaddingStart{l2IndexEnd << (L2Bits - L1Bits)};
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size_t l1EndPaddingEnd{end >> L1Bits};
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if (l1EndPaddingStart != l1EndPaddingEnd) {
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auto &l2Entry{level2Table[l2IndexEnd]};
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if (l2Entry.valid) {
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l2Entry.valid = false;
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l2Entry.level1Set = true;
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for (size_t i{l1EndPaddingStart}; i < l1EndPaddingEnd; i++)
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level1Table[i] = range;
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for (size_t i{l1EndPaddingEnd}; i < l1EndPaddingStart + L1inL2Count; i++)
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level1Table[i] = l2Entry.range;
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} else if (!l2Entry.level1Set) {
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l2Entry.range = range;
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l2Entry.valid = true;
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l2Entry.level1Set = false;
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} else {
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for (size_t i{l1EndPaddingStart}; i < l1EndPaddingEnd; i++)
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level1Table[i] = range;
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}
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}
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}
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/* Helpers for pointer-based access */
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template<typename T>
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requires std::is_pointer_v<T>
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const RangeType &operator[](T pointer) const {
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return (*this)[reinterpret_cast<size_t>(pointer)];
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}
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template<typename T>
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requires std::is_pointer_v<T>
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void Set(T pointer, RangeType range) {
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Set(reinterpret_cast<size_t>(pointer), range);
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}
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template<typename T>
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requires std::is_pointer_v<T>
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void Set(T start, T end, RangeType range) {
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Set(reinterpret_cast<size_t>(start), reinterpret_cast<size_t>(end), range);
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}
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void Set(span<u8> span, RangeType range) {
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Set(reinterpret_cast<size_t>(span.begin().base()), reinterpret_cast<size_t>(span.end().base()));
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}
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};
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}
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