fix: reliability improvements in WinServer/IPC subsystems

kernel/src/Api/WinServer.cpp

@@ -142,7 +142,7 @@ namespace WinServer {
         FillSurfaceLocked(snapshot, w, h, InitialWindowPixel);
 
         uint64_t userVa = 0;
-        if (Ipc::MapSurfaceForPid(live, ownerPid, ownerPml4, heapNext, userVa) != 0) {
+        if (Ipc::MapSurfaceForPid(live, ownerPid, ownerPml4, heapNext, userVa, false) != 0) {
             Ipc::ReleaseMailbox(mailbox, true, true);
             Ipc::ReleaseSurface(snapshot);
             Ipc::ReleaseSurface(live);
@@ -242,7 +242,7 @@ namespace WinServer {
         if (!slot.used || slot.snapshotSurface == nullptr) return 0;
 
         uint64_t outVa = 0;
-        if (Ipc::MapSurfaceForPid(slot.snapshotSurface, callerPid, callerPml4, heapNext, outVa) != 0) {
+        if (Ipc::MapSurfaceForPid(slot.snapshotSurface, callerPid, callerPml4, heapNext, outVa, false) != 0) {
             return 0;
         }
         return outVa;
@@ -294,7 +294,7 @@ namespace WinServer {
         Ipc::RetainSurface(newSnapshot);
 
         uint64_t newOwnerVa = 0;
-        if (Ipc::MapSurfaceForPid(newLive, callerPid, ownerPml4, heapNext, newOwnerVa) != 0) {
+        if (Ipc::MapSurfaceForPid(newLive, callerPid, ownerPml4, heapNext, newOwnerVa, false) != 0) {
             Ipc::ReleaseSurface(newSnapshot);
             Ipc::ReleaseSurface(newLive);
             return -1;

kernel/src/Ipc/Ipc.cpp

@@ -1806,7 +1806,8 @@ namespace Ipc {
         return 0;
     }
 
-    int MapSurfaceForPid(Surface* surface, int pid, uint64_t pml4Phys, uint64_t& heapNext, uint64_t& outVa) {
+    int MapSurfaceForPid(Surface* surface, int pid, uint64_t pml4Phys, uint64_t& heapNext,
+                         uint64_t& outVa, bool reserveGrowthRange) {
         if (surface == nullptr) return -1;
 
         int slot = SlotForPid(pid);
@@ -1862,20 +1863,14 @@ namespace Ipc {
         g_surfaceMaps[slot][mapIdx].numPages = numPages;
         surface->refs++;  // inlined RetainRawObject — we already hold surface->lock
 
-        // Reserve the full surface address-range cap, not just the currently
-        // mapped pages.  ResizeSurface can grow this surface up to
-        // MaxSurfacePages, and its grow path extends the existing VA range
-        // in-place by mapping new pages at baseVa + p*0x1000 for p beyond the
-        // original size.  If we only bumped heapNext by numPages*0x1000, any
-        // subsequent mapping (another surface, heap allocation, etc.) would
-        // sit at baseVa + numPages*0x1000 -- and a later grow would silently
-        // overwrite its PTEs.  Reserving MaxSurfacePages*0x1000 (32 MiB) of
-        // VA per mapping is cheap: 47-bit user VA gives 128 TiB of headroom,
-        // and at most MaxSurfaceMapsPerProcess (64) mappings per process
-        // means at most 2 GiB of reserved VA per process.  Page tables are
-        // only populated for pages actually mapped; unused VA in the
-        // reservation costs nothing beyond the address-space slot.
-        heapNext += (uint64_t)MaxSurfacePages * 0x1000ULL;
+        // Generic IPC surfaces can grow in place through ResizeSurface(), so
+        // their mapping must reserve the maximum VA range that a later grow
+        // can populate.  Window-server surfaces are replaced rather than grown
+        // in place, so callers can opt out and avoid burning 32 MiB of process
+        // VA on every window map/remap during a long desktop session.
+        uint32_t reservedPages = reserveGrowthRange ? MaxSurfacePages : numPages;
+        if (reservedPages < numPages) reservedPages = numPages;
+        heapNext += (uint64_t)reservedPages * 0x1000ULL;
         outVa = baseVa;
         surface->lock.Release();
         return 0;

kernel/src/Ipc/Ipc.hpp

@@ -135,7 +135,8 @@ namespace Ipc {
                             uint32_t fillPixel);
     uint64_t MapSurfaceHandle(int handle);
     int ResizeSurfaceHandle(int handle, uint64_t newSize);
-    int MapSurfaceForPid(Surface* surface, int pid, uint64_t pml4Phys, uint64_t& heapNext, uint64_t& outVa);
+    int MapSurfaceForPid(Surface* surface, int pid, uint64_t pml4Phys, uint64_t& heapNext,
+                         uint64_t& outVa, bool reserveGrowthRange = true);
     int UnmapSurfaceForPid(Surface* surface, int pid, uint64_t pml4Phys);
 
     ProcessObject* GetProcessObject(int pid);