NVIDIA: SAUCE: vfio/nvgrace-egm: list gpus through sysfs

To replicate the host EGM topology in the VM in terms of
the GPU affinity, the userspace need to be aware of which
GPUs belong to the same socket as the EGM region.

Expose the list of GPUs associated with an EGM region
through sysfs. The list can be queried from the location
/sys/devices/virtual/egm/egmX/gpu_devices.

Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Ref: sj24: /home/nvidia/ankita/kernel_patches/0002_vfio_nvgrace-egm_list_gpus_through_sysfs.patch
(koba: Enchance error handling for sysfs_create_group)
Signed-off-by: Koba Ko <kobak@nvidia.com>
Acked-by: Matthew R. Ochs <mochs@nvidia.com>
Acked-by: Carol L. Soto <csoto@nvidia.com>
Signed-off-by: Matthew R. Ochs <mochs@nvidia.com>
(cherry picked from commit fec2356 https://github.com/NVIDIA/NV-Kernels/tree/24.04_linux-nvidia-adv-6.11-next)
Signed-off-by: Nirmoy Das <nirmoyd@nvidia.com>

Author: ankita-nv

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

@@ -357,6 +357,38 @@ static void nvgrace_egm_fetch_bad_pages(struct pci_dev *pdev,
 	memunmap(memaddr);
 }
 
+static ssize_t gpu_devices_show(struct device *dev, struct device_attribute *attr,
+                               char *buf)
+{
+       struct egm_region *region =
+               container_of(dev, struct egm_region, device);
+       struct gpu_node *node, *temp_node;
+       int len = 0;
+
+       list_for_each_entry_safe(node, temp_node, &region->gpus, list) {
+               struct pci_dev *pdev = node->pdev;
+
+               len += sysfs_emit_at(buf, len, "%04x:%02x:%02x.%x\n",
+                                    pci_domain_nr(pdev->bus),
+                                    pdev->bus->number,
+                                    PCI_SLOT(pdev->devfn),
+                                    PCI_FUNC(pdev->devfn));
+       }
+
+       return len;
+}
+
+static DEVICE_ATTR_RO(gpu_devices);
+
+static struct attribute *attrs[] = {
+       &dev_attr_gpu_devices.attr,
+       NULL,
+};
+
+static struct attribute_group attr_group = {
+       .attrs = attrs,
+};
+
 static int add_gpu(struct egm_region *region, struct pci_dev *pdev)
 {
        struct gpu_node *node;
@@ -423,12 +455,18 @@ int register_egm_node(struct pci_dev *pdev)
 
 	list_add_tail(&region->list, &egm_list);
 
-	ret = add_gpu(region, pdev);
+	ret = sysfs_create_group(&region->device.kobj, &attr_group);
 	if (ret)
 		goto err_remove_from_list;
 
+	ret = add_gpu(region, pdev);
+	if (ret)
+		goto err_remove_sysfs;
+
 	return 0;
 
+err_remove_sysfs:
+        sysfs_remove_group(&region->device.kobj, &attr_group);
 err_remove_from_list:
 	list_del(&region->list);
 	destroy_egm_chardev(region);
@@ -462,6 +500,7 @@ void unregister_egm_node(struct pci_dev *pdev)
 				vfree(cur_page);
 			}
 
+			sysfs_remove_group(&region->device.kobj, &attr_group);
 			destroy_egm_chardev(region);
 			list_del(&region->list);
 			kfree(region);