From 5d2fc0147ea0f998c34c85d9ef058fe98fef75ec Mon Sep 17 00:00:00 2001
From: "Admiral H. Curtiss" <pikachu025@gmail.com>
Date: Thu, 30 Nov 2023 22:17:10 +0100
Subject: [PATCH 1/4] MMU: Mark IsOpcodeFlag() and IsNoExceptionFlag() as
 constexpr.

---
 Source/Core/Core/PowerPC/MMU.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Source/Core/Core/PowerPC/MMU.cpp b/Source/Core/Core/PowerPC/MMU.cpp
index aa305fe0ab..db5d4a4b31 100644
--- a/Source/Core/Core/PowerPC/MMU.cpp
+++ b/Source/Core/Core/PowerPC/MMU.cpp
@@ -85,12 +85,12 @@ MMU::~MMU() = default;
   return Common::swap64(val);
 }
 
-static bool IsOpcodeFlag(XCheckTLBFlag flag)
+static constexpr bool IsOpcodeFlag(XCheckTLBFlag flag)
 {
   return flag == XCheckTLBFlag::Opcode || flag == XCheckTLBFlag::OpcodeNoException;
 }
 
-static bool IsNoExceptionFlag(XCheckTLBFlag flag)
+static constexpr bool IsNoExceptionFlag(XCheckTLBFlag flag)
 {
   return flag == XCheckTLBFlag::NoException || flag == XCheckTLBFlag::OpcodeNoException;
 }

From 0d6a0724fd946e6f9e25dc2f965d409eab3db741 Mon Sep 17 00:00:00 2001
From: "Admiral H. Curtiss" <pikachu025@gmail.com>
Date: Thu, 30 Nov 2023 22:15:50 +0100
Subject: [PATCH 2/4] MMU: Always use data read for the PTE lookup in
 TranslatePageAddress.

---
 Source/Core/Core/PowerPC/MMU.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Source/Core/Core/PowerPC/MMU.cpp b/Source/Core/Core/PowerPC/MMU.cpp
index db5d4a4b31..6c85fc54ee 100644
--- a/Source/Core/Core/PowerPC/MMU.cpp
+++ b/Source/Core/Core/PowerPC/MMU.cpp
@@ -1464,11 +1464,13 @@ MMU::TranslateAddressResult MMU::TranslatePageAddress(const EffectiveAddress add
 
     for (int i = 0; i < 8; i++, pteg_addr += 8)
     {
-      const u32 pteg = ReadFromHardware<flag, u32, true>(pteg_addr);
+      constexpr XCheckTLBFlag pte_read_flag =
+          IsNoExceptionFlag(flag) ? XCheckTLBFlag::NoException : XCheckTLBFlag::Read;
+      const u32 pteg = ReadFromHardware<pte_read_flag, u32, true>(pteg_addr);
 
       if (pte1.Hex == pteg)
       {
-        UPTE_Hi pte2(ReadFromHardware<flag, u32, true>(pteg_addr + 4));
+        UPTE_Hi pte2(ReadFromHardware<pte_read_flag, u32, true>(pteg_addr + 4));
 
         // set the access bits
         switch (flag)

From c12725c916caac69d33e1d5c040930eed9e9cb70 Mon Sep 17 00:00:00 2001
From: "Admiral H. Curtiss" <pikachu025@gmail.com>
Date: Thu, 30 Nov 2023 22:17:26 +0100
Subject: [PATCH 3/4] MMU: Assert that the given XCheckTLBFlag is valid for the
 operation.

---
 Source/Core/Core/PowerPC/MMU.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Source/Core/Core/PowerPC/MMU.cpp b/Source/Core/Core/PowerPC/MMU.cpp
index 6c85fc54ee..a069d14073 100644
--- a/Source/Core/Core/PowerPC/MMU.cpp
+++ b/Source/Core/Core/PowerPC/MMU.cpp
@@ -148,6 +148,12 @@ static void EFB_Write(u32 data, u32 addr)
 template <XCheckTLBFlag flag, typename T, bool never_translate>
 T MMU::ReadFromHardware(u32 em_address)
 {
+  // ReadFromHardware is currently used with XCheckTLBFlag::OpcodeNoException by host instruction
+  // functions. Actual instruction decoding (which can raise exceptions and uses icache) is handled
+  // by TryReadInstruction.
+  static_assert(flag == XCheckTLBFlag::NoException || flag == XCheckTLBFlag::Read ||
+                flag == XCheckTLBFlag::OpcodeNoException);
+
   const u32 em_address_start_page = em_address & ~HW_PAGE_MASK;
   const u32 em_address_end_page = (em_address + sizeof(T) - 1) & ~HW_PAGE_MASK;
   if (em_address_start_page != em_address_end_page)
@@ -258,6 +264,8 @@ T MMU::ReadFromHardware(u32 em_address)
 template <XCheckTLBFlag flag, bool never_translate>
 void MMU::WriteToHardware(u32 em_address, const u32 data, const u32 size)
 {
+  static_assert(flag == XCheckTLBFlag::NoException || flag == XCheckTLBFlag::Write);
+
   DEBUG_ASSERT(size <= 4);
 
   const u32 em_address_start_page = em_address & ~HW_PAGE_MASK;

From a0da6788a36399f3e42a28dc6f1d5c28f549955c Mon Sep 17 00:00:00 2001
From: "Admiral H. Curtiss" <pikachu025@gmail.com>
Date: Sat, 19 Nov 2022 02:29:04 +0100
Subject: [PATCH 4/4] MMU: Use MSR.IR for instruction reads.

---
 Source/Core/Core/PowerPC/MMU.cpp | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Source/Core/Core/PowerPC/MMU.cpp b/Source/Core/Core/PowerPC/MMU.cpp
index a069d14073..fdd370acc4 100644
--- a/Source/Core/Core/PowerPC/MMU.cpp
+++ b/Source/Core/Core/PowerPC/MMU.cpp
@@ -172,7 +172,8 @@ T MMU::ReadFromHardware(u32 em_address)
 
   bool wi = false;
 
-  if (!never_translate && m_ppc_state.msr.DR)
+  if (!never_translate &&
+      (IsOpcodeFlag(flag) ? m_ppc_state.msr.IR.Value() : m_ppc_state.msr.DR.Value()))
   {
     auto translated_addr = TranslateAddress<flag>(em_address);
     if (!translated_addr.Success())
@@ -516,7 +517,7 @@ std::optional<ReadResult<u32>> MMU::HostTryReadInstruction(const Core::CPUThread
   case RequestedAddressSpace::Effective:
   {
     const u32 value = mmu.ReadFromHardware<XCheckTLBFlag::OpcodeNoException, u32>(address);
-    return ReadResult<u32>(!!mmu.m_ppc_state.msr.DR, value);
+    return ReadResult<u32>(!!mmu.m_ppc_state.msr.IR, value);
   }
   case RequestedAddressSpace::Physical:
   {
@@ -525,7 +526,7 @@ std::optional<ReadResult<u32>> MMU::HostTryReadInstruction(const Core::CPUThread
   }
   case RequestedAddressSpace::Virtual:
   {
-    if (!mmu.m_ppc_state.msr.DR)
+    if (!mmu.m_ppc_state.msr.IR)
       return std::nullopt;
     const u32 value = mmu.ReadFromHardware<XCheckTLBFlag::OpcodeNoException, u32>(address);
     return ReadResult<u32>(true, value);