diff --git a/sycl/source/detail/sycl_mem_obj_t.hpp b/sycl/source/detail/sycl_mem_obj_t.hpp
index 4893d154a7566..60593231848a7 100644
--- a/sycl/source/detail/sycl_mem_obj_t.hpp
+++ b/sycl/source/detail/sycl_mem_obj_t.hpp
@@ -165,16 +165,6 @@ class SYCLMemObjT : public SYCLMemObjI {
            has_property<property::image::use_host_ptr>();
   }
 
-  bool canReadHostPtr(void *HostPtr, const size_t RequiredAlign) {
-    bool Aligned =
-        (reinterpret_cast<std::uintptr_t>(HostPtr) % RequiredAlign) == 0;
-    return Aligned || useHostPtr();
-  }
-
-  bool canReuseHostPtr(void *HostPtr, const size_t RequiredAlign) {
-    return !MHostPtrReadOnly && canReadHostPtr(HostPtr, RequiredAlign);
-  }
-
   void handleHostData(void *HostPtr, const size_t RequiredAlign) {
     MHostPtrProvided = true;
     if (!MHostPtrReadOnly && HostPtr) {
@@ -184,10 +174,16 @@ class SYCLMemObjT : public SYCLMemObjI {
     }
 
     if (HostPtr) {
-      if (canReuseHostPtr(HostPtr, RequiredAlign)) {
-        MUserPtr = HostPtr;
-      } else if (canReadHostPtr(HostPtr, RequiredAlign)) {
-        MUserPtr = HostPtr;
+      // Pass the user pointer to UR unchanged. Each adapter is responsible
+      // for handling pointers it cannot use directly (misaligned, not
+      // importable, etc.) by allocating its own backing storage and copying.
+      MUserPtr = HostPtr;
+
+      // For a read-only host pointer we still need a writable backing store
+      // if the user later creates a write accessor. Defer the allocation
+      // until that happens. This is adapter-independent: the language rule
+      // is that we may not write through a const user pointer.
+      if (MHostPtrReadOnly) {
         std::lock_guard<std::mutex> Lock(MCreateShadowCopyMtx);
         MCreateShadowCopy = [this, RequiredAlign, HostPtr]() -> void {
           setAlign(RequiredAlign);
@@ -195,11 +191,6 @@ class SYCLMemObjT : public SYCLMemObjI {
           MUserPtr = MShadowCopy;
           std::memcpy(MUserPtr, HostPtr, MSizeInBytes);
         };
-      } else {
-        setAlign(RequiredAlign);
-        MShadowCopy = allocateHostMem();
-        MUserPtr = MShadowCopy;
-        std::memcpy(MUserPtr, HostPtr, MSizeInBytes);
       }
     }
   }
@@ -218,10 +209,9 @@ class SYCLMemObjT : public SYCLMemObjI {
       if (!MHostPtrReadOnly)
         set_final_data_from_storage();
 
-      if (canReuseHostPtr(HostPtr.get(), RequiredAlign)) {
-        MUserPtr = HostPtr.get();
-      } else if (canReadHostPtr(HostPtr.get(), RequiredAlign)) {
-        MUserPtr = HostPtr.get();
+      MUserPtr = HostPtr.get();
+
+      if (MHostPtrReadOnly) {
         std::lock_guard<std::mutex> Lock(MCreateShadowCopyMtx);
         MCreateShadowCopy = [this, RequiredAlign, HostPtr]() -> void {
           setAlign(RequiredAlign);
@@ -229,11 +219,6 @@ class SYCLMemObjT : public SYCLMemObjI {
           MUserPtr = MShadowCopy;
           std::memcpy(MUserPtr, HostPtr.get(), MSizeInBytes);
         };
-      } else {
-        setAlign(RequiredAlign);
-        MShadowCopy = allocateHostMem();
-        MUserPtr = MShadowCopy;
-        std::memcpy(MUserPtr, HostPtr.get(), MSizeInBytes);
       }
     }
   }
diff --git a/sycl/test-e2e/Regression/buffer_shadow_copy_platform_policy.cpp b/sycl/test-e2e/Regression/buffer_shadow_copy_platform_policy.cpp
new file mode 100644
index 0000000000000..9177be4aab34d
--- /dev/null
+++ b/sycl/test-e2e/Regression/buffer_shadow_copy_platform_policy.cpp
@@ -0,0 +1,261 @@
+// RUN: %{build} -o %t.out
+// RUN: %{run} %t.out
+
+#include <sycl/detail/core.hpp>
+
+#include <cstddef>
+#include <cstring>
+#include <iostream>
+#include <memory>
+#include <vector>
+
+// Read-only kernel: sum all elements and return the result.
+static int runReadOnlySumKernel(sycl::queue &Q, const int *HostPtr, size_t N) {
+  sycl::buffer<int, 1> Buf(HostPtr, sycl::range<1>(N),
+                           {sycl::property::buffer::use_host_ptr{}});
+  sycl::buffer<int, 1> SumBuf(1);
+
+  Q.submit([&](sycl::handler &CGH) {
+    auto InAcc = Buf.get_access<sycl::access::mode::read>(CGH);
+    auto SumAcc = SumBuf.get_access<sycl::access::mode::write>(CGH);
+    CGH.single_task([=]() {
+      int Sum = 0;
+      for (size_t I = 0; I < N; ++I)
+        Sum += InAcc[I];
+      SumAcc[0] = Sum;
+    });
+  });
+  Q.wait_and_throw();
+
+  auto SumHostAcc = SumBuf.get_host_access();
+  return SumHostAcc[0];
+}
+
+// Writable kernel path; buffer destruction happens at scope exit.
+static void runWriteKernel(sycl::queue &Q, int *HostPtr, size_t N) {
+  {
+    sycl::buffer<int, 1> Buf(HostPtr, sycl::range<1>(N),
+                             {sycl::property::buffer::use_host_ptr{}});
+
+    Q.submit([&](sycl::handler &CGH) {
+      auto OutAcc = Buf.get_access<sycl::access::mode::write>(CGH);
+      CGH.single_task([=]() {
+        for (size_t I = 0; I < N; ++I)
+          OutAcc[I] = static_cast<int>(I * 3 + 7);
+      });
+    });
+    Q.wait_and_throw();
+  }
+}
+
+// Verifies host-side result after writable-buffer destruction.
+static bool checkExpectedPattern(const int *Ptr, size_t N) {
+  std::vector<int> Tmp(N);
+  std::memcpy(Tmp.data(), Ptr, sizeof(int) * N);
+  for (size_t I = 0; I < N; ++I) {
+    if (Tmp[I] != static_cast<int>(I * 3 + 7))
+      return false;
+  }
+  return true;
+}
+
+// Exercises the map/unmap path: a mid-lifetime host_accessor on a live buffer.
+// This is the path that, on adapters keeping a separate working buffer (e.g.
+// L0v2 integrated with a non-importable pointer), must keep the user pointer
+// and the device-visible buffer in sync in BOTH directions. The buffer is
+// local to this function, so it is destroyed on return; the caller then checks
+// the final write-back at HostPtr.
+//
+// Sequence: kernel writes I -> host reads (map READ) and verifies -> host adds
+// 100 (unmap WRITE-back) -> kernel adds 1 -> scope exit writes I+101 to host.
+static bool runMidLifeHostAccessor(sycl::queue &Q, int *HostPtr, size_t N) {
+  sycl::buffer<int, 1> Buf(HostPtr, sycl::range<1>(N),
+                           {sycl::property::buffer::use_host_ptr{}});
+
+  Q.submit([&](sycl::handler &CGH) {
+    auto Acc = Buf.get_access<sycl::access::mode::write>(CGH);
+    CGH.single_task([=]() {
+      for (size_t I = 0; I < N; ++I)
+        Acc[I] = static_cast<int>(I);
+    });
+  });
+  Q.wait_and_throw();
+
+  // Mid-lifetime host access: map READ must observe the kernel's writes, and
+  // the modification must survive back to the device on unmap WRITE.
+  {
+    sycl::host_accessor HAcc(Buf, sycl::read_write);
+    for (size_t I = 0; I < N; ++I) {
+      if (HAcc[I] != static_cast<int>(I))
+        return false;
+      HAcc[I] += 100;
+    }
+  }
+
+  Q.submit([&](sycl::handler &CGH) {
+    auto Acc = Buf.get_access<sycl::access::mode::read_write>(CGH);
+    CGH.single_task([=]() {
+      for (size_t I = 0; I < N; ++I)
+        Acc[I] += 1;
+    });
+  });
+  Q.wait_and_throw();
+
+  return true;
+}
+
+// A read-only buffer must never modify the user's source data, regardless of
+// whether the backend aliases the pointer (zero-copy) or copies it. Portable
+// across all backends because a read-only access performs no writes.
+static bool runReadOnlyImmutability(sycl::queue &Q, const int *HostPtr,
+                                    size_t N) {
+  std::vector<int> Orig(N);
+  std::memcpy(Orig.data(), HostPtr, sizeof(int) * N);
+
+  {
+    sycl::buffer<int, 1> Buf(HostPtr, sycl::range<1>(N),
+                             {sycl::property::buffer::use_host_ptr{}});
+    sycl::buffer<int, 1> SumBuf(1);
+    Q.submit([&](sycl::handler &CGH) {
+      auto In = Buf.get_access<sycl::access::mode::read>(CGH);
+      auto S = SumBuf.get_access<sycl::access::mode::write>(CGH);
+      CGH.single_task([=]() {
+        int Sum = 0;
+        for (size_t I = 0; I < N; ++I)
+          Sum += In[I];
+        S[0] = Sum;
+      });
+    });
+    Q.wait_and_throw();
+  }
+
+  return std::memcmp(Orig.data(), HostPtr, sizeof(int) * N) == 0;
+}
+
+int main() {
+  constexpr size_t N = 32;
+  sycl::queue Q;
+
+  // Build aligned reference data.
+  std::vector<int> AlignedInput(N);
+  for (size_t I = 0; I < N; ++I)
+    AlignedInput[I] = static_cast<int>(I);
+
+  const int ExpectedSum = static_cast<int>((N - 1) * N / 2);
+
+  auto checkMidLife = [](const int *Ptr) {
+    std::vector<int> Tmp(N);
+    std::memcpy(Tmp.data(), Ptr, sizeof(int) * N);
+    for (size_t I = 0; I < N; ++I)
+      if (Tmp[I] != static_cast<int>(I + 101))
+        return false;
+    return true;
+  };
+
+  // --- Aligned baseline ---
+  if (runReadOnlySumKernel(Q, AlignedInput.data(), N) != ExpectedSum) {
+    std::cerr << "Unexpected aligned sum\n";
+    return 1;
+  }
+
+  std::vector<int> AlignedWritable(N, 0);
+  runWriteKernel(Q, AlignedWritable.data(), N);
+  if (!checkExpectedPattern(AlignedWritable.data(), N)) {
+    std::cerr << "Unexpected data in aligned writable buffer\n";
+    return 1;
+  }
+
+  if (!runReadOnlyImmutability(Q, AlignedInput.data(), N)) {
+    std::cerr << "Read-only buffer modified aligned source data\n";
+    return 1;
+  }
+
+  std::vector<int> AlignedMid(N, 0);
+  if (!runMidLifeHostAccessor(Q, AlignedMid.data(), N) ||
+      !checkMidLife(AlignedMid.data())) {
+    std::cerr << "Mid-life host_accessor failed on aligned buffer\n";
+    return 1;
+  }
+
+  // --- Misaligned variants ---
+  // Cover several offsets. 1 byte is not even int-aligned; 4 bytes is
+  // int-aligned but typically below a backend's required base-address
+  // alignment (e.g. CL_DEVICE_MEM_BASE_ADDR_ALIGN is normally 64-128 B);
+  // 64 bytes exercises the boundary case where some backends still require
+  // a stricter (e.g. 128 B / page) alignment for zero-copy import.
+  constexpr size_t Offsets[] = {1, 4, 64};
+  for (size_t Offset : Offsets) {
+    std::vector<unsigned char> ROStorage(sizeof(int) * N + Offset);
+    int *UnalignedPtr = reinterpret_cast<int *>(ROStorage.data() + Offset);
+    std::memcpy(UnalignedPtr, AlignedInput.data(), sizeof(int) * N);
+    const int *ReadOnlyUnalignedPtr = UnalignedPtr;
+
+    if (runReadOnlySumKernel(Q, ReadOnlyUnalignedPtr, N) != ExpectedSum) {
+      std::cerr << "Unexpected misaligned sum (offset=" << Offset << ")\n";
+      return 1;
+    }
+
+    std::vector<unsigned char> WritableStorage(sizeof(int) * N + Offset, 0);
+    int *UnalignedWritablePtr =
+        reinterpret_cast<int *>(WritableStorage.data() + Offset);
+    runWriteKernel(Q, UnalignedWritablePtr, N);
+    if (!checkExpectedPattern(UnalignedWritablePtr, N)) {
+      std::cerr << "Unexpected data in misaligned writable buffer (offset="
+                << Offset << ")\n";
+      return 1;
+    }
+
+    if (!runReadOnlyImmutability(Q, ReadOnlyUnalignedPtr, N)) {
+      std::cerr << "Read-only buffer modified misaligned source data (offset="
+                << Offset << ")\n";
+      return 1;
+    }
+
+    std::vector<unsigned char> MidStorage(sizeof(int) * N + Offset, 0);
+    int *UnalignedMidPtr = reinterpret_cast<int *>(MidStorage.data() + Offset);
+    if (!runMidLifeHostAccessor(Q, UnalignedMidPtr, N) ||
+        !checkMidLife(UnalignedMidPtr)) {
+      std::cerr << "Mid-life host_accessor failed on misaligned buffer (offset="
+                << Offset << ")\n";
+      return 1;
+    }
+  }
+
+  // --- Aligned-but-non-importable: raw heap allocation ---
+  // A plain new[] returns a pointer that is naturally aligned for int but
+  // is not USM-imported, not pinned, and not part of any device-visible
+  // allocation. On L0 this exercises the path where maybeImportUSM either
+  // succeeds (and the pointer is promoted) or fails and the adapter must
+  // fall back to its own backing storage with explicit copies.
+  {
+    std::unique_ptr<int[]> HeapInput(new int[N]);
+    for (size_t I = 0; I < N; ++I)
+      HeapInput[I] = static_cast<int>(I);
+
+    if (runReadOnlySumKernel(Q, HeapInput.get(), N) != ExpectedSum) {
+      std::cerr << "Unexpected sum on aligned heap pointer\n";
+      return 1;
+    }
+
+    std::unique_ptr<int[]> HeapWritable(new int[N]());
+    runWriteKernel(Q, HeapWritable.get(), N);
+    if (!checkExpectedPattern(HeapWritable.get(), N)) {
+      std::cerr << "Unexpected data in aligned heap writable buffer\n";
+      return 1;
+    }
+
+    if (!runReadOnlyImmutability(Q, HeapInput.get(), N)) {
+      std::cerr << "Read-only buffer modified aligned heap source data\n";
+      return 1;
+    }
+
+    std::unique_ptr<int[]> HeapMid(new int[N]());
+    if (!runMidLifeHostAccessor(Q, HeapMid.get(), N) ||
+        !checkMidLife(HeapMid.get())) {
+      std::cerr << "Mid-life host_accessor failed on aligned heap buffer\n";
+      return 1;
+    }
+  }
+
+  return 0;
+}
diff --git a/unified-runtime/source/adapters/level_zero/common.hpp b/unified-runtime/source/adapters/level_zero/common.hpp
index af5976fa8aa53..b70c4fb2bf00a 100644
--- a/unified-runtime/source/adapters/level_zero/common.hpp
+++ b/unified-runtime/source/adapters/level_zero/common.hpp
@@ -328,8 +328,8 @@ class ZeUSMImportExtension {
   ZeUSMImportExtension() : Supported{false}, Enabled{false} {}
 
   void setZeUSMImport(ur_platform_handle_t_ *Platform);
-  void doZeUSMImport(ze_driver_handle_t DriverHandle, void *HostPtr,
-                     size_t Size);
+  ze_result_t doZeUSMImport(ze_driver_handle_t DriverHandle, void *HostPtr,
+                            size_t Size);
   void doZeUSMRelease(ze_driver_handle_t DriverHandle, void *HostPtr);
 };
 
diff --git a/unified-runtime/source/adapters/level_zero/device.cpp b/unified-runtime/source/adapters/level_zero/device.cpp
index 638df58eea1c3..49e690af3b5f5 100644
--- a/unified-runtime/source/adapters/level_zero/device.cpp
+++ b/unified-runtime/source/adapters/level_zero/device.cpp
@@ -2388,10 +2388,10 @@ void ZeUSMImportExtension::setZeUSMImport(ur_platform_handle_t_ *Platform) {
     setEnvVar("SYCL_HOST_UNIFIED_MEMORY", "1");
   }
 }
-void ZeUSMImportExtension::doZeUSMImport(ze_driver_handle_t DriverHandle,
-                                         void *HostPtr, size_t Size) {
-  ZE_CALL_NOCHECK(zexDriverImportExternalPointer,
-                  (DriverHandle, HostPtr, Size));
+ze_result_t ZeUSMImportExtension::doZeUSMImport(ze_driver_handle_t DriverHandle,
+                                                void *HostPtr, size_t Size) {
+  return ZE_CALL_NOCHECK(zexDriverImportExternalPointer,
+                         (DriverHandle, HostPtr, Size));
 }
 void ZeUSMImportExtension::doZeUSMRelease(ze_driver_handle_t DriverHandle,
                                           void *HostPtr) {
diff --git a/unified-runtime/source/adapters/level_zero/helpers/memory_helpers.cpp b/unified-runtime/source/adapters/level_zero/helpers/memory_helpers.cpp
index 51a75bbd5fc75..44f5e792b638a 100644
--- a/unified-runtime/source/adapters/level_zero/helpers/memory_helpers.cpp
+++ b/unified-runtime/source/adapters/level_zero/helpers/memory_helpers.cpp
@@ -31,9 +31,11 @@ bool maybeImportUSM(ze_driver_handle_t hTranslatedDriver,
   auto ret = getMemoryAttrs(hContext, ptr, nullptr, &properties);
 
   if (ret == UR_RESULT_SUCCESS && properties.type == ZE_MEMORY_TYPE_UNKNOWN) {
-    // Promote the host ptr to USM host memory
-    ZeUSMImport.doZeUSMImport(hTranslatedDriver, ptr, size);
-    return true;
+    // Promote the host ptr to USM host memory. The driver-level import can
+    // fail (e.g., for a misaligned ptr), so report success to callers only
+    // when the underlying L0 call actually succeeded.
+    return ZeUSMImport.doZeUSMImport(hTranslatedDriver, ptr, size) ==
+           ZE_RESULT_SUCCESS;
   }
   return false;
 }