From ca42578d4ecd9aae22a26bd3bb6a12631f0da9ab Mon Sep 17 00:00:00 2001
From: CamilleLaVey <camillelavey99@gmail.com>
Date: Sun, 8 Mar 2026 15:55:06 -0400
Subject: [PATCH] [nce] Added "tainted" page fault handling inside dual channel

---
 src/core/arm/nce/arm_nce.cpp | 22 ++++++++++++++++++++--
 src/core/arm/nce/arm_nce.h   | 10 ++++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/core/arm/nce/arm_nce.cpp b/src/core/arm/nce/arm_nce.cpp
index 807a8ba919..909bdbe046 100644
--- a/src/core/arm/nce/arm_nce.cpp
+++ b/src/core/arm/nce/arm_nce.cpp
@@ -44,6 +44,7 @@ fpsimd_context* GetFloatingPointState(mcontext_t& host_ctx) {
 using namespace Common::Literals;
 constexpr u32 StackSize = 128_KiB;
 constexpr u64 SplitPageAccessWindow = 64;
+constexpr size_t MaxPreciseAccessPages = 256;
 
 [[nodiscard]] constexpr u64 AlignDownPage(u64 addr) {
     return addr & ~u64{Memory::YUZU_PAGEMASK};
@@ -191,15 +192,18 @@ bool ArmNce::HandleGuestAccessFault(GuestContext* guest_ctx, void* raw_info, voi
     auto& host_ctx = static_cast<ucontext_t*>(raw_context)->uc_mcontext;
     auto* fpctx = GetFloatingPointState(host_ctx);
     auto* info = static_cast<siginfo_t*>(raw_info);
+    auto* parent = guest_ctx->parent;
 
     const u64 fault_addr = reinterpret_cast<u64>(info->si_addr);
     const Common::ProcessAddress addr = fault_addr & ~Memory::YUZU_PAGEMASK;
     const u64 page_offset = fault_addr & Memory::YUZU_PAGEMASK;
-    auto& memory = guest_ctx->parent->m_running_thread->GetOwnerProcess()->GetMemory();
-    const bool prefer_precise_channel = ShouldUsePreciseAccessChannel(guest_ctx, fault_addr);
+    auto& memory = parent->m_running_thread->GetOwnerProcess()->GetMemory();
+    const bool prefer_precise_channel = ShouldUsePreciseAccessChannel(guest_ctx, fault_addr) ||
+                                        parent->IsPreciseAccessPage(fault_addr);
 
     if (prefer_precise_channel) {
         if (auto next_pc = MatchAndExecuteOneInstruction(memory, &host_ctx, fpctx); next_pc) {
+            parent->MarkPreciseAccessPage(fault_addr);
             host_ctx.pc = *next_pc;
             return true;
         }
@@ -220,6 +224,7 @@ bool ArmNce::HandleGuestAccessFault(GuestContext* guest_ctx, void* raw_info, voi
     }
 
     if (auto next_pc = MatchAndExecuteOneInstruction(memory, &host_ctx, fpctx); next_pc) {
+        parent->MarkPreciseAccessPage(fault_addr);
         host_ctx.pc = *next_pc;
         return true;
     }
@@ -236,6 +241,19 @@ void ArmNce::HandleHostAccessFault(int sig, void* raw_info, void* raw_context) {
     return g_orig_segv_action.sa_sigaction(sig, static_cast<siginfo_t*>(raw_info), raw_context);
 }
 
+bool ArmNce::IsPreciseAccessPage(u64 addr) const {
+    const std::scoped_lock lk{m_precise_pages_guard};
+    return m_precise_pages.contains(AlignDownPage(addr));
+}
+
+void ArmNce::MarkPreciseAccessPage(u64 addr) {
+    const std::scoped_lock lk{m_precise_pages_guard};
+    if (m_precise_pages.size() >= MaxPreciseAccessPages) {
+        m_precise_pages.clear();
+    }
+    m_precise_pages.insert(AlignDownPage(addr));
+}
+
 void ArmNce::LockThread(Kernel::KThread* thread) {
     auto* thread_params = &thread->GetNativeExecutionParameters();
     LockThreadParameters(thread_params);
diff --git a/src/core/arm/nce/arm_nce.h b/src/core/arm/nce/arm_nce.h
index be9b304c4c..8be293055c 100644
--- a/src/core/arm/nce/arm_nce.h
+++ b/src/core/arm/nce/arm_nce.h
@@ -1,9 +1,13 @@
+// SPDX-FileCopyrightText: Copyright 2026 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
 
 #pragma once
 
 #include <mutex>
+#include <unordered_set>
 
 #include "core/arm/arm_interface.h"
 #include "core/arm/nce/guest_context.h"
@@ -77,6 +81,9 @@ private:
     static void HandleHostAlignmentFault(int sig, void* info, void* raw_context);
     static void HandleHostAccessFault(int sig, void* info, void* raw_context);
 
+    bool IsPreciseAccessPage(u64 addr) const;
+    void MarkPreciseAccessPage(u64 addr);
+
 public:
     Core::System& m_system;
 
@@ -88,6 +95,9 @@ public:
     GuestContext m_guest_ctx{};
     Kernel::KThread* m_running_thread{};
 
+    mutable std::mutex m_precise_pages_guard{};
+    std::unordered_set<u64> m_precise_pages{};
+
     // Stack for signal processing.
     std::unique_ptr<u8[]> m_stack{};
 };