diff options
| author | ReinUsesLisp <reinuseslisp@airmail.cc> | 2020-12-29 21:16:57 -0300 |
|---|---|---|
| committer | ReinUsesLisp <reinuseslisp@airmail.cc> | 2020-12-29 21:54:49 -0300 |
| commit | b3587102d160fb74a12935a79f06ee8a12712f12 (patch) | |
| tree | 2afb7123bafef085cb97fc97f96be1aaf8c3a660 /src/common/page_table.h | |
| parent | 8d55c8c85543459adf199408884f0b0b1c3a3c90 (diff) | |
core/memory: Read and write page table atomically
Squash attributes into the pointer's integer, making them an uintptr_t
pair containing 2 bits at the bottom and then the pointer. These bits
are currently unused thanks to alignment requirements.
Configure Dynarmic to mask out these bits on pointer reads.
While we are at it, remove some unused attributes carried over from
Citra.
Read/Write and other hot functions use a two step unpacking process that
is less readable to stop MSVC from emitting an extra AND instruction in
the hot path:
mov rdi,rcx
shr rdx,0Ch
mov r8,qword ptr [rax+8]
mov rax,qword ptr [r8+rdx*8]
mov rdx,rax
-and al,3
and rdx,0FFFFFFFFFFFFFFFCh
je Core::Memory::Memory::Impl::Read<unsigned char>
mov rax,qword ptr [vaddr]
movzx eax,byte ptr [rdx+rax]
Diffstat (limited to 'src/common/page_table.h')
| -rw-r--r-- | src/common/page_table.h | 68 |
1 files changed, 57 insertions, 11 deletions
diff --git a/src/common/page_table.h b/src/common/page_table.h index 9754fabf91..8d4ee92498 100644 --- a/src/common/page_table.h +++ b/src/common/page_table.h @@ -4,6 +4,7 @@ #pragma once +#include <atomic> #include <tuple> #include "common/common_types.h" @@ -20,10 +21,6 @@ enum class PageType : u8 { /// Page is mapped to regular memory, but also needs to check for rasterizer cache flushing and /// invalidation RasterizerCachedMemory, - /// Page is mapped to a I/O region. Writing and reading to this page is handled by functions. - Special, - /// Page is allocated for use. - Allocated, }; struct SpecialRegion { @@ -48,6 +45,59 @@ struct SpecialRegion { * mimics the way a real CPU page table works. */ struct PageTable { + /// Number of bits reserved for attribute tagging. + /// This can be at most the guaranteed alignment of the pointers in the page table. + static constexpr int ATTRIBUTE_BITS = 2; + + /** + * Pair of host pointer and page type attribute. + * This uses the lower bits of a given pointer to store the attribute tag. + * Writing and reading the pointer attribute pair is guaranteed to be atomic for the same method + * call. In other words, they are guaranteed to be synchronized at all times. + */ + class PageInfo { + public: + /// Returns the page pointer + [[nodiscard]] u8* Pointer() const noexcept { + return ExtractPointer(raw.load(std::memory_order_relaxed)); + } + + /// Returns the page type attribute + [[nodiscard]] PageType Type() const noexcept { + return ExtractType(raw.load(std::memory_order_relaxed)); + } + + /// Returns the page pointer and attribute pair, extracted from the same atomic read + [[nodiscard]] std::pair<u8*, PageType> PointerType() const noexcept { + const uintptr_t non_atomic_raw = raw.load(std::memory_order_relaxed); + return {ExtractPointer(non_atomic_raw), ExtractType(non_atomic_raw)}; + } + + /// Returns the raw representation of the page information. + /// Use ExtractPointer and ExtractType to unpack the value. + [[nodiscard]] uintptr_t Raw() const noexcept { + return raw.load(std::memory_order_relaxed); + } + + /// Write a page pointer and type pair atomically + void Store(u8* pointer, PageType type) noexcept { + raw.store(reinterpret_cast<uintptr_t>(pointer) | static_cast<uintptr_t>(type)); + } + + /// Unpack a pointer from a page info raw representation + [[nodiscard]] static u8* ExtractPointer(uintptr_t raw) noexcept { + return reinterpret_cast<u8*>(raw & (~uintptr_t{0} << ATTRIBUTE_BITS)); + } + + /// Unpack a page type from a page info raw representation + [[nodiscard]] static PageType ExtractType(uintptr_t raw) noexcept { + return static_cast<PageType>(raw & ((uintptr_t{1} << ATTRIBUTE_BITS) - 1)); + } + + private: + std::atomic<uintptr_t> raw; + }; + PageTable(); ~PageTable() noexcept; @@ -63,20 +113,16 @@ struct PageTable { * * @param address_space_width_in_bits The address size width in bits. * @param page_size_in_bits The page size in bits. - * @param has_attribute Whether or not this page has any backing attributes. */ - void Resize(std::size_t address_space_width_in_bits, std::size_t page_size_in_bits, - bool has_attribute); + void Resize(size_t address_space_width_in_bits, size_t page_size_in_bits); /** * Vector of memory pointers backing each page. An entry can only be non-null if the - * corresponding entry in the `attributes` vector is of type `Memory`. + * corresponding attribute element is of type `Memory`. */ - VirtualBuffer<u8*> pointers; + VirtualBuffer<PageInfo> pointers; VirtualBuffer<u64> backing_addr; - - VirtualBuffer<PageType> attributes; }; } // namespace Common |