From 21e5d6e6d7f7ed0aa28a950db5b95ccd64999a44 Mon Sep 17 00:00:00 2001
From: SeMmy <semmytrane@gmail.com>
Date: Thu, 2 Apr 2026 10:53:39 -0400
Subject: [PATCH] fix(windows): skip hybrid GPU hook on single-GPU systems to
 prevent dxgi.dll crash

The NtGdiDdDDIGetCachedHybridQueryValue hook was introduced in #3530 to prevent
DXGI output reparenting on multi-GPU/hybrid systems. On single-GPU systems, this
hook is unnecessary and causes an access violation (0xc0000005) in dxgi.dll at a
consistent offset on Windows 11 24H2 build 29558+.

The crash occurs because dxgi.dll's internal code path doesn't correctly handle
the spoofed D3DKMT_GPU_PREFERENCE_STATE_UNSPECIFIED value on newer Windows builds,
resulting in a crash loop where the service wrapper continuously restarts the process.

This fix:
- Enumerates DXGI adapters before installing the hook to detect single vs multi-GPU
- Deduplicates adapters by VendorId+DeviceId (same physical GPU can appear as
  multiple DXGI adapters due to cross-adapter copies)
- Skips the hook entirely on single-GPU systems where output reparenting is not
  a concern
- Adds error handling for MH_Initialize and MH_CreateHookApi return values
- Adds logging for hook installation status

Tested on: RTX 4070 Ti (single GPU), Windows 11 24H2 build 29558, NVIDIA 591.86

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Guided-By: SeMmy
---
 src/platform/windows/display_base.cpp | 50 ++++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 4 deletions(-)

diff --git a/src/platform/windows/display_base.cpp b/src/platform/windows/display_base.cpp
index e42bb8efa4b..132d928b921 100644
--- a/src/platform/windows/display_base.cpp
+++ b/src/platform/windows/display_base.cpp
@@ -4,6 +4,7 @@
  */
 // standard includes
 #include <cmath>
+#include <set>
 #include <thread>
 
 // platform includes
@@ -458,10 +459,51 @@ namespace platf::dxgi {
       }
 
       {
-        // We aren't calling MH_Uninitialize(), but that's okay because this hook lasts for the life of the process
-        MH_Initialize();
-        MH_CreateHookApi(L"win32u.dll", "NtGdiDdDDIGetCachedHybridQueryValue", (void *) NtGdiDdDDIGetCachedHybridQueryValueHook, nullptr);
-        MH_EnableHook(MH_ALL_HOOKS);
+        // The hybrid GPU workaround hooks NtGdiDdDDIGetCachedHybridQueryValue to prevent
+        // DXGI output reparenting that breaks DDA on multi-GPU systems. On single-GPU
+        // systems, this hook is unnecessary and can cause crashes on some Windows builds
+        // (e.g., Windows 11 24H2 build 29558+) where dxgi.dll doesn't handle the spoofed
+        // GPU preference state correctly, resulting in an access violation.
+        bool needs_hybrid_workaround = false;
+        {
+          IDXGIFactory1 *probe_factory = nullptr;
+          if (SUCCEEDED(CreateDXGIFactory1(IID_IDXGIFactory1, (void **) &probe_factory))) {
+            // Count unique physical GPUs by VendorId+DeviceId.
+            // DXGI can present the same physical GPU as multiple logical adapters
+            // (e.g., cross-adapter copies), so we deduplicate.
+            std::set<std::pair<UINT, UINT>> unique_gpus;
+            IDXGIAdapter1 *probe_adapter = nullptr;
+            for (int i = 0; probe_factory->EnumAdapters1(i, &probe_adapter) != DXGI_ERROR_NOT_FOUND; ++i) {
+              DXGI_ADAPTER_DESC1 desc;
+              probe_adapter->GetDesc1(&desc);
+              if (!(desc.Flags & DXGI_ADAPTER_FLAG_SOFTWARE)) {
+                unique_gpus.emplace(desc.VendorId, desc.DeviceId);
+              }
+              probe_adapter->Release();
+            }
+            probe_factory->Release();
+            needs_hybrid_workaround = unique_gpus.size() > 1;
+            if (!needs_hybrid_workaround) {
+              BOOST_LOG(info) << "Single GPU detected, skipping hybrid GPU output reparenting workaround"sv;
+            }
+          }
+        }
+
+        if (needs_hybrid_workaround) {
+          // We aren't calling MH_Uninitialize(), but that's okay because this hook lasts for the life of the process
+          auto mh_status = MH_Initialize();
+          if (mh_status == MH_OK || mh_status == MH_ERROR_ALREADY_INITIALIZED) {
+            mh_status = MH_CreateHookApi(L"win32u.dll", "NtGdiDdDDIGetCachedHybridQueryValue", (void *) NtGdiDdDDIGetCachedHybridQueryValueHook, nullptr);
+            if (mh_status == MH_OK) {
+              MH_EnableHook(MH_ALL_HOOKS);
+              BOOST_LOG(info) << "Installed hybrid GPU output reparenting workaround"sv;
+            } else {
+              BOOST_LOG(warning) << "Failed to hook NtGdiDdDDIGetCachedHybridQueryValue (MH status: "sv << mh_status << "), skipping hybrid GPU workaround"sv;
+            }
+          } else {
+            BOOST_LOG(warning) << "Failed to initialize MinHook (MH status: "sv << mh_status << "), skipping hybrid GPU workaround"sv;
+          }
+        }
       }
     });