NVIDIA: SAUCE: vfio/nvgrace-gpu: Avoid resmem pfn unregistration

On platforms without the mig HW bug (e.g. Grace-Blackwell) there is not a
requirement to create the resmem region. Accordingly, this region is not
configured on these platforms, which leads to the following print when the
device is closed:

resource: Trying to free nonexistent resource <0x0000000000000000-0x000000000000ffff>

Avoid calling unregister_pfn_address_space for resmem when the region is
not being used.

Fixes: 2d21b7b ("vfio/nvgrace-gpu: register device memory for poison handling")

Signed-off-by: Matthew R. Ochs <[email protected]>
Acked-by: Carol L. Soto <[email protected]>
Acked-by: Nirmoy Das <[email protected]>
Signed-off-by: Matthew R. Ochs <[email protected]>
(cherry picked from commit bd0187d https://github.com/NVIDIA/NV-Kernels/tree/24.04_linux-nvidia-adv-6.11-next)
Signed-off-by: Nirmoy Das <[email protected]>

Author: nvmochs

drivers/vfio/pci/nvgrace-gpu/main.c

@@ -239,7 +239,8 @@ static void nvgrace_gpu_close_device(struct vfio_device *core_vdev)
 	mutex_destroy(&nvdev->remap_lock);
 
 #ifdef CONFIG_MEMORY_FAILURE
-	unregister_pfn_address_space(&nvdev->resmem.pfn_address_space);
+	if (nvdev->resmem.memlength)
+		unregister_pfn_address_space(&nvdev->resmem.pfn_address_space);
 	unregister_pfn_address_space(&nvdev->usemem.pfn_address_space);
 #endif
 	vfio_pci_core_close_device(core_vdev);
@@ -320,9 +321,10 @@ static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
 #ifdef CONFIG_MEMORY_FAILURE
 	vma->vm_ops = &nvgrace_gpu_vfio_pci_mmap_ops;
 
-	if (index == VFIO_PCI_BAR2_REGION_INDEX)
+	if (index == VFIO_PCI_BAR2_REGION_INDEX) {
+		WARN_ON_ONCE(!nvdev->has_mig_hw_bug);
 		ret = nvgrace_gpu_vfio_pci_register_pfn_range(&nvdev->resmem, vma);
-	else
+	} else
 		ret = nvgrace_gpu_vfio_pci_register_pfn_range(&nvdev->usemem, vma);
 #endif