[core] Finalize AliasRegionExtraSize (#291)

The previous implementation was based on assumptions for the baseline.
The new implementation is based on calculations, and should be more robust for DRAM values beyond 8GB as well.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/291
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: Shinmegumi <shinmegumi@eden-emu.dev>
Co-authored-by: SDK-Chan <sdkchan@eden-emu.dev>
Co-committed-by: SDK-Chan <sdkchan@eden-emu.dev>

src/core/hle/kernel/k_page_table_base.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -290,6 +293,23 @@ Result KPageTableBase::InitializeForProcess(Svc::CreateProcessFlag as_type, bool
         alloc_start = process_code_end;
         alloc_size = GetInteger(end) - GetInteger(process_code_end);
     }
+
+    // FW 18+: Apply extra region size calculations for already available region size
+    const auto as_mask = Svc::CreateProcessFlag::AddressSpaceMask;
+    const bool is_64bit_as = (as_type & as_mask) == Svc::CreateProcessFlag::AddressSpace64Bit;
+
+    if (is_64bit_as && (as_type & Svc::CreateProcessFlag::EnableAliasRegionExtraSize)
+        != Svc::CreateProcessFlag{0} && alias_region_size) {
+        const size_t address_space_size = (GetInteger(end) - GetInteger(start));
+
+        // Same as address_space_size/8 but faster due to bit shifting operation
+        const size_t alias_region_extra_size = address_space_size >> 3;
+        alias_region_size += alias_region_extra_size;
+
+        // Store for later processing
+        m_alias_region_extra_size = alias_region_extra_size;
+    }
+
     const size_t needed_size =
         (alias_region_size + heap_region_size + stack_region_size + kernel_map_region_size);
     R_UNLESS(alloc_size >= needed_size, ResultOutOfMemory);

src/core/hle/kernel/k_page_table_base.h

@@ -211,6 +211,7 @@ private:
     size_t m_mapped_unsafe_physical_memory{};
     size_t m_mapped_insecure_memory{};
     size_t m_mapped_ipc_server_memory{};
+    size_t m_alias_region_extra_size{};
     mutable KLightLock m_general_lock;
     mutable KLightLock m_map_physical_memory_lock;
     KLightLock m_device_map_lock;
@@ -698,6 +699,10 @@ public:
         return m_alias_code_region_end - m_alias_code_region_start;
     }
 
+    size_t GetAliasRegionExtraSize() const {
+        return m_alias_region_extra_size;
+    }
+
     size_t GetNormalMemorySize() const {
         // Lock the table.
         KScopedLightLock lk(m_general_lock);
@@ -718,17 +723,6 @@ public:
         return m_address_space_width;
     }
 
-    size_t CalculateAliasRegionExtraSize() const {
-        const size_t baseline = 64ull << 30;   // Mostly appropriate for DRAM values <= 8GB
-        const size_t region = GetAliasRegionSize();
-
-        if (region > baseline) {
-            return region - baseline;
-        }
-
-        return 0;
-    }
-
 public:
     // Linear mapped
     static u8* GetLinearMappedVirtualPointer(KernelCore& kernel, KPhysicalAddress addr) {

src/core/hle/kernel/k_process_page_table.h

@@ -414,7 +414,7 @@ public:
         return m_page_table.GetAliasRegionSize();
     }
     size_t GetAliasRegionExtraSize() const {
-        return m_page_table.CalculateAliasRegionExtraSize();
+        return m_page_table.GetAliasRegionExtraSize();
     }
     size_t GetStackRegionSize() const {
         return m_page_table.GetStackRegionSize();

src/core/hle/kernel/svc_types.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 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
 
@@ -643,9 +646,13 @@ enum class CreateProcessFlag : u32 {
     // 11.x+ DisableDeviceAddressSpaceMerge.
     DisableDeviceAddressSpaceMerge = (1 << 12),
 
+    // 18.x+ Add extra size to the already available AliasRegionSize
+    EnableAliasRegionExtraSize = (1 << 13),
+
     // Mask of all flags.
     All = Is64Bit | AddressSpaceMask | EnableDebug | EnableAslr | IsApplication |
-          PoolPartitionMask | OptimizeMemoryAllocation | DisableDeviceAddressSpaceMerge,
+          PoolPartitionMask | OptimizeMemoryAllocation | DisableDeviceAddressSpaceMerge |
+          EnableAliasRegionExtraSize,
 };
 DECLARE_ENUM_FLAG_OPERATORS(CreateProcessFlag);