[hle] reuse previous pagetable when initializing new processes on the same KProcessPageTable (#3891)

VirtualBuffer<> would be recreated each time due to the `operator=()` from the unique_ptr<> when initializing a new process, this change makes it so said thing doesn't happen (instead it resizes the existing buffer)

this means that consecutive launches of the same process that happen to have the same process page table (or reuse it) will no longer incur a ctor/dtor path for VirtualBuffer and instead just resize the existing one

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3891
Reviewed-by: crueter <crueter@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

src/common/page_table.h

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 // SPDX-FileCopyrightText: Copyright 2019 yuzu Emulator Project
@@ -142,10 +142,8 @@ struct PageTable {
     VirtualBuffer<PageEntryData> entries;
     static_assert(sizeof(PageEntryData) == 32);
 
-    std::size_t current_address_space_width_in_bits{};
-
     u8* fastmem_arena{};
-
+    std::size_t current_address_space_width_in_bits{};
     std::size_t page_size{};
 };
 

src/common/virtual_buffer.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -21,7 +24,9 @@ public:
     //     "with the current allocator");
 
     constexpr VirtualBuffer() = default;
-    explicit VirtualBuffer(std::size_t count) : alloc_size{count * sizeof(T)} {
+    explicit VirtualBuffer(std::size_t count) noexcept
+        : alloc_size{count * sizeof(T)}
+    {
         base_ptr = reinterpret_cast<T*>(AllocateMemoryPages(alloc_size));
     }
 
@@ -33,8 +38,8 @@ public:
     VirtualBuffer& operator=(const VirtualBuffer&) = delete;
 
     VirtualBuffer(VirtualBuffer&& other) noexcept
-        : alloc_size{std::exchange(other.alloc_size, 0)}, base_ptr{std::exchange(other.base_ptr),
-                                                                   nullptr} {}
+        : alloc_size{std::exchange(other.alloc_size, 0)}, base_ptr{std::exchange(other.base_ptr), nullptr}
+    {}
 
     VirtualBuffer& operator=(VirtualBuffer&& other) noexcept {
         alloc_size = std::exchange(other.alloc_size, 0);
@@ -42,35 +47,31 @@ public:
         return *this;
     }
 
-    void resize(std::size_t count) {
-        const auto new_size = count * sizeof(T);
-        if (new_size == alloc_size) {
-            return;
+    void resize(std::size_t count) noexcept {
+        if (auto const new_size = count * sizeof(T); new_size != alloc_size) {
+            FreeMemoryPages(base_ptr, alloc_size);
+            alloc_size = new_size;
+            base_ptr = reinterpret_cast<T*>(AllocateMemoryPages(alloc_size));
         }
-
-        FreeMemoryPages(base_ptr, alloc_size);
-
-        alloc_size = new_size;
-        base_ptr = reinterpret_cast<T*>(AllocateMemoryPages(alloc_size));
     }
 
-    [[nodiscard]] constexpr const T& operator[](std::size_t index) const {
+    [[nodiscard]] constexpr const T& operator[](std::size_t index) const noexcept {
         return base_ptr[index];
     }
 
-    [[nodiscard]] constexpr T& operator[](std::size_t index) {
+    [[nodiscard]] constexpr T& operator[](std::size_t index) noexcept {
         return base_ptr[index];
     }
 
-    [[nodiscard]] constexpr T* data() {
+    [[nodiscard]] constexpr T* data() noexcept {
         return base_ptr;
     }
 
-    [[nodiscard]] constexpr const T* data() const {
+    [[nodiscard]] constexpr const T* data() const noexcept {
         return base_ptr;
     }
 
-    [[nodiscard]] constexpr std::size_t size() const {
+    [[nodiscard]] constexpr std::size_t size() const noexcept {
         return alloc_size / sizeof(T);
     }