vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

This is the way user to invoke hot-reset for the devices opened by cdev
interface. User should check the flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED
in the output of VFIO_DEVICE_GET_PCI_HOT_RESET_INFO ioctl before doing
hot-reset for cdev devices.
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Yanting Jiang <yanting.jiang@intel.com>
Tested-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20230718105542.4138-11-yi.l.liu@intel.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci_core.c

@@ -181,7 +181,8 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)
 struct vfio_pci_group_info;
 static void vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set);
 static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
-				      struct vfio_pci_group_info *groups);
+				      struct vfio_pci_group_info *groups,
+				      struct iommufd_ctx *iommufd_ctx);
 
 /*
  * INTx masking requires the ability to disable INTx signaling via PCI_COMMAND
@@ -1329,8 +1330,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev,
 	if (ret)
 		return ret;
 
-	/* Somewhere between 1 and count is OK */
-	if (!array_count || array_count > count)
+	if (array_count > count)
 		return -EINVAL;
 
 	group_fds = kcalloc(array_count, sizeof(*group_fds), GFP_KERNEL);
@@ -1379,7 +1379,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev,
 	info.count = array_count;
 	info.files = files;
 
-	ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info);
+	ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info, NULL);
 
 hot_reset_release:
 	for (file_idx--; file_idx >= 0; file_idx--)
@@ -1402,13 +1402,21 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev,
 	if (hdr.argsz < minsz || hdr.flags)
 		return -EINVAL;
 
+	/* zero-length array is only for cdev opened devices */
+	if (!!hdr.count == vfio_device_cdev_opened(&vdev->vdev))
+		return -EINVAL;
+
 	/* Can we do a slot or bus reset or neither? */
 	if (!pci_probe_reset_slot(vdev->pdev->slot))
 		slot = true;
 	else if (pci_probe_reset_bus(vdev->pdev->bus))
 		return -ENODEV;
 
-	return vfio_pci_ioctl_pci_hot_reset_groups(vdev, hdr.count, slot, arg);
+	if (hdr.count)
+		return vfio_pci_ioctl_pci_hot_reset_groups(vdev, hdr.count, slot, arg);
+
+	return vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, NULL,
+					  vfio_iommufd_device_ictx(&vdev->vdev));
 }
 
 static int vfio_pci_ioctl_ioeventfd(struct vfio_pci_core_device *vdev,
@@ -2376,13 +2384,16 @@ const struct pci_error_handlers vfio_pci_core_err_handlers = {
 };
 EXPORT_SYMBOL_GPL(vfio_pci_core_err_handlers);
 
-static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev,
+static bool vfio_dev_in_groups(struct vfio_device *vdev,
 			       struct vfio_pci_group_info *groups)
 {
 	unsigned int i;
 
+	if (!groups)
+		return false;
+
 	for (i = 0; i < groups->count; i++)
-		if (vfio_file_has_dev(groups->files[i], &vdev->vdev))
+		if (vfio_file_has_dev(groups->files[i], vdev))
 			return true;
 	return false;
 }
@@ -2458,7 +2469,8 @@ static int vfio_pci_dev_set_pm_runtime_get(struct vfio_device_set *dev_set)
  * get each memory_lock.
  */
 static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
-				      struct vfio_pci_group_info *groups)
+				      struct vfio_pci_group_info *groups,
+				      struct iommufd_ctx *iommufd_ctx)
 {
 	struct vfio_pci_core_device *cur_mem;
 	struct vfio_pci_core_device *cur_vma;
@@ -2488,11 +2500,38 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
 		goto err_unlock;
 
 	list_for_each_entry(cur_vma, &dev_set->device_list, vdev.dev_set_list) {
+		bool owned;
+
 		/*
-		 * Test whether all the affected devices are contained by the
-		 * set of groups provided by the user.
+		 * Test whether all the affected devices can be reset by the
+		 * user.
+		 *
+		 * If called from a group opened device and the user provides
+		 * a set of groups, all the devices in the dev_set should be
+		 * contained by the set of groups provided by the user.
+		 *
+		 * If called from a cdev opened device and the user provides
+		 * a zero-length array, all the devices in the dev_set must
+		 * be bound to the same iommufd_ctx as the input iommufd_ctx.
+		 * If there is any device that has not been bound to any
+		 * iommufd_ctx yet, check if its iommu_group has any device
+		 * bound to the input iommufd_ctx.  Such devices can be
+		 * considered owned by the input iommufd_ctx as the device
+		 * cannot be owned by another iommufd_ctx when its iommu_group
+		 * is owned.
+		 *
+		 * Otherwise, reset is not allowed.
 		 */
-		if (!vfio_dev_in_groups(cur_vma, groups)) {
+		if (iommufd_ctx) {
+			int devid = vfio_iommufd_get_dev_id(&cur_vma->vdev,
+							    iommufd_ctx);
+
+			owned = (devid > 0 || devid == -ENOENT);
+		} else {
+			owned = vfio_dev_in_groups(&cur_vma->vdev, groups);
+		}
+
+		if (!owned) {
 			ret = -EINVAL;
 			goto err_undo;
 		}

include/uapi/linux/vfio.h

@@ -717,6 +717,9 @@ enum {
  *	  affected devices are represented in the dev_set and also owned by
  *	  the user.  This flag is available only when
  *	  flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID is set, otherwise reserved.
+ *	  When set, user could invoke VFIO_DEVICE_PCI_HOT_RESET with a zero
+ *	  length fd array on the calling device as the ownership is validated
+ *	  by iommufd_ctx.
  *
  * Return: 0 on success, -errno on failure:
  *	-enospc = insufficient buffer, -enodev = unsupported for device.
@@ -748,6 +751,24 @@ struct vfio_pci_hot_reset_info {
  * VFIO_DEVICE_PCI_HOT_RESET - _IOW(VFIO_TYPE, VFIO_BASE + 13,
  *				    struct vfio_pci_hot_reset)
  *
+ * A PCI hot reset results in either a bus or slot reset which may affect
+ * other devices sharing the bus/slot.  The calling user must have
+ * ownership of the full set of affected devices as determined by the
+ * VFIO_DEVICE_GET_PCI_HOT_RESET_INFO ioctl.
+ *
+ * When called on a device file descriptor acquired through the vfio
+ * group interface, the user is required to provide proof of ownership
+ * of those affected devices via the group_fds array in struct
+ * vfio_pci_hot_reset.
+ *
+ * When called on a direct cdev opened vfio device, the flags field of
+ * struct vfio_pci_hot_reset_info reports the ownership status of the
+ * affected devices and this ioctl must be called with an empty group_fds
+ * array.  See above INFO ioctl definition for ownership requirements.
+ *
+ * Mixed usage of legacy groups and cdevs across the set of affected
+ * devices is not supported.
+ *
  * Return: 0 on success, -errno on failure.
  */
 struct vfio_pci_hot_reset {