Return NoOpDeviceGuardImpl in replace of CudaDeviceGuard when device is not available, or cpu-only build (#160532)

Summary:

To support exporting a cuda model on a CPU-only machine under fake tensor mode.
User commonly need to move sample inputs to the cuda device with .to("cuda:0") or .to("cuda") call.
This diff supports this.
I expect the following pattern to work
```
with FakeTensorMode(allow_non_fake_inputs=True):
    cuda_module = module.to("cuda:0")
    cuda_sample_inputs = tuple([x.to("cuda:0") for x in sample_inputs])
    with torch.no_grad():
        ep = torch.export.export(cuda_module, cuda_sample_inputs)
```

Test Plan:
CI

Rollback Plan:

Differential Revision: D80181887

Pull Request resolved: https://github.com/pytorch/pytorch/pull/160532
Approved by: https://github.com/henryoier, https://github.com/ezyang

c10/core/impl/DeviceGuardImplInterface.cpp

@@ -1,4 +1,5 @@
 #include <c10/core/impl/DeviceGuardImplInterface.h>
+#include <c10/core/impl/FakeGuardImpl.h>
 #include <array>
 
 namespace c10::impl {
@@ -14,4 +15,27 @@ DeviceGuardImplRegistrar::DeviceGuardImplRegistrar(
   device_guard_impl_registry[static_cast<size_t>(type)].store(impl);
 }
 
+namespace {
+thread_local std::unique_ptr<DeviceGuardImplInterface> tls_fake_device_guard =
+    nullptr;
+}
+
+void ensureCUDADeviceGuardSet() {
+  constexpr auto cuda_idx = static_cast<std::size_t>(DeviceType::CUDA);
+
+  const DeviceGuardImplInterface* p =
+      device_guard_impl_registry[cuda_idx].load();
+
+  // A non-null `ptr` indicates that CUDA is already available.
+  if (p == nullptr || (p && p->deviceCount() == 0)) {
+    // In following cases, we override CUDA guard interface with a no-op
+    // device guard.
+    // 1. p == nullptr; Trying to get a cuda device guard on a cpu-only build.
+    // 2. p->deviceCount() == 0; cuda build enabled, but no cuda devices
+    // available.
+    tls_fake_device_guard = std::make_unique<FakeGuardImpl<DeviceType::CUDA>>();
+    device_guard_impl_registry[cuda_idx].store(tls_fake_device_guard.get());
+  }
+}
+
 } // namespace c10::impl

c10/core/impl/DeviceGuardImplInterface.h

@@ -6,6 +6,7 @@
 #include <c10/util/Exception.h>
 
 // Just for C10_ANONYMOUS_VARIABLE
+#include <c10/core/impl/TorchDispatchModeTLS.h>
 #include <c10/util/Registry.h>
 
 #include <array>
@@ -251,7 +252,7 @@ struct C10_API DeviceGuardImplInterface {
 // for devices that don't actually have a concept of device index.  Prominent
 // examples are CPU and Meta.
 template <DeviceType D>
-struct NoOpDeviceGuardImpl final : public DeviceGuardImplInterface {
+struct NoOpDeviceGuardImpl : public DeviceGuardImplInterface {
   NoOpDeviceGuardImpl() = default;
   DeviceType type() const override {
     return D;
@@ -371,5 +372,7 @@ inline bool hasDeviceGuardImpl(DeviceType type) {
   return device_guard_impl_registry[static_cast<size_t>(type)].load();
 }
 
+void C10_API ensureCUDADeviceGuardSet();
+
 } // namespace impl
 } // namespace c10

test/export/test_export_opinfo.py

@@ -3,6 +3,7 @@
 # flake8: noqa
 
 import itertools
+import unittest
 
 import torch
 from torch._subclasses.fake_tensor import FakeTensor, FakeTensorMode
@@ -50,17 +51,11 @@ fake_export_failures = {
     xfail("masked.std"),
     xfail("masked.sum"),
     xfail("masked.var"),
-    xfail("nn.functional.grid_sample"),
     xfail("to_sparse"),
     # cannot xfail as it is passing for cpu-only build
+    skip("nn.functional.grid_sample"),
     skip("nn.functional.conv2d"),
     skip("nn.functional.scaled_dot_product_attention"),
-    # following are failing due to OptionalDeviceGuard
-    xfail("__getitem__"),
-    xfail("nn.functional.batch_norm"),
-    xfail("nn.functional.instance_norm"),
-    xfail("nn.functional.multi_margin_loss"),
-    xfail("nonzero"),
 }
 
 fake_decomposition_failures = {
@@ -128,9 +123,52 @@ class TestExportOpInfo(TestCase):
     def test_fake_export(self, device, dtype, op):
         _test_export_helper(self, dtype, op)
 
+    @unittest.skipIf(not torch.backends.cuda.is_built(), "requires CUDA build")
+    def test_preserve_original_behavior(self):
+        def cuda_calls_behavior_unchanged():
+            cpu_x = torch.randn(2)
+            with self.assertRaisesRegex(
+                RuntimeError, "Found no NVIDIA driver on your system."
+            ):
+                cuda_x = cpu_x.to("cuda")
 
-only_for = "cpu"
-instantiate_device_type_tests(TestExportOpInfo, globals(), only_for=only_for)
+            with self.assertRaisesRegex(
+                RuntimeError, "Found no NVIDIA driver on your system."
+            ):
+                torch.randn(2, device="cuda")
+
+            with self.assertRaisesRegex(
+                RuntimeError, "Found no NVIDIA driver on your system."
+            ):
+                torch.cuda.get_device_capability()
+
+            with self.assertRaisesRegex(
+                RuntimeError, "Found no NVIDIA driver on your system."
+            ):
+                torch.cuda.set_device(1)
+
+            with self.assertRaisesRegex(
+                RuntimeError, "Found no NVIDIA driver on your system."
+            ):
+                torch.cuda.current_device()
+
+            self.assertEqual(torch.cuda.is_available(), False)
+            self.assertEqual(torch.cuda.device_count(), 0)
+
+        cuda_calls_behavior_unchanged()
+
+        cpu_x = torch.randn(2)
+        with FakeTensorMode(allow_non_fake_inputs=True) as mode:
+            cuda_x = mode.from_tensor(cpu_x)
+            cuda_x.fake_device = torch.device("cuda")
+            cuda_y = cuda_x + cuda_x
+            self.assertEqual(cuda_y.device.type, "cuda")
+
+        # should fail again after exiting the fake mode, with the identical error message
+        cuda_calls_behavior_unchanged()
+
+
+instantiate_device_type_tests(TestExportOpInfo, globals(), only_for="cpu")
 
 
 if __name__ == "__main__":

torch/_C/__init__.pyi.in

@@ -1379,6 +1379,7 @@ def _get_linalg_preferred_backend() -> _LinalgBackend: ...
 def _set_linalg_preferred_backend(arg: _LinalgBackend): ...
 def _get_fp32_precision_getter(backend: str, op: str) -> str: ...
 def _set_fp32_precision_setter(backend: str, op: str, value: str) -> str: ...
+def _ensureCUDADeviceGuardSet() -> None: ...
 
 class _LinalgBackend:
     Default: _LinalgBackend

torch/_subclasses/fake_tensor.py

@@ -1387,6 +1387,12 @@ class FakeTensorMode(TorchDispatchMode):
             # See NOTE: [torch.tensor, lift_fresh, and device movement]
             prev_only_lift_cpu_tensors = torch._C._only_lift_cpu_tensors()
             torch._C._set_only_lift_cpu_tensors(True)
+
+            # In the case of CPU-only build or cuda device unavailable,
+            # we patch the cuda device guard to use NoOpDeviceGuardImpl.
+            # This enables us to trace over cuda kernels under FakeTensorMode.
+            torch._C._ensureCUDADeviceGuardSet()
+
         maybe_prev_fake_mode = torch._C._unset_dispatch_mode(self._mode_key)
         if self is not maybe_prev_fake_mode:
             self.enter_stack.append(
@@ -1397,6 +1403,7 @@ class FakeTensorMode(TorchDispatchMode):
             # no-op (still need to re-set the fake mode though since we unset it)
             torch._C._set_dispatch_mode(self)
             self.enter_stack.append((False, None, prev_only_lift_cpu_tensors))
+
         return self
 
     def __exit__(

torch/csrc/Module.cpp

@@ -26,6 +26,7 @@
 #include <ATen/native/Normalization.h>
 #include <c10/core/Device.h>
 #include <c10/core/DispatchKeySet.h>
+#include <c10/core/impl/DeviceGuardImplInterface.h>
 #include <c10/util/AbortHandler.h>
 #include <c10/util/Backtrace.h>
 #include <c10/util/Logging.h>
@@ -1550,6 +1551,15 @@ static PyObject* THPModule_are_vmap_fallback_warnings_enabled(
   END_HANDLE_TH_ERRORS
 }
 
+static PyObject* THCPModule_ensureCUDADeviceGuardSet(
+    PyObject* self,
+    PyObject* noargs) {
+  HANDLE_TH_ERRORS
+  c10::impl::ensureCUDADeviceGuardSet();
+  Py_RETURN_NONE;
+  END_HANDLE_TH_ERRORS
+}
+
 static std::initializer_list<PyMethodDef> TorchMethods = {
     {"_initExtension", THPModule_initExtension, METH_O, nullptr},
     {"_autograd_init", THPAutograd_initExtension, METH_NOARGS, nullptr},
@@ -1845,7 +1855,13 @@ static std::initializer_list<PyMethodDef> TorchMethods = {
      (PyCFunction)(void (*)())THPModule_has_torch_function_variadic,
      METH_FASTCALL,
      nullptr},
-    {nullptr, nullptr, 0, nullptr}};
+    {"_ensureCUDADeviceGuardSet",
+     THCPModule_ensureCUDADeviceGuardSet,
+     METH_NOARGS,
+     nullptr},
+    {nullptr, nullptr, 0, nullptr}
+
+};
 
 #ifdef USE_CUDA
 // NOLINTBEGIN(misc-use-internal-linkage)