[PATCH v2 05/10] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

[Yi Liu <yi.l.liu@intel.com>]

as an alternative method for ownership check when iommufd is used. In
this case all opened devices in the affected dev_set are verified to
be bound to a same valid iommufd value to allow reset. It's simpler
and faster as user does not need to pass a set of fds and kernel no
need to search the device within the given fds.

a device in noiommu mode doesn't have a valid iommufd, so this method
should not be used in a dev_set which contains multiple devices and one
of them is in noiommu. The only allowed noiommu scenario is that the
calling device is noiommu and it's in a singleton dev_set.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
---
 drivers/vfio/pci/vfio_pci_core.c | 42 +++++++++++++++++++++++++++-----
 include/uapi/linux/vfio.h        |  9 ++++++-
 2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 3696b8e58445..b68fcba67a4b 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -180,7 +180,8 @@ 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
@@ -1277,7 +1278,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev,
 		return ret;
 
 	/* Somewhere between 1 and count is OK */
-	if (!hdr->count || hdr->count > count)
+	if (hdr->count > count)
 		return -EINVAL;
 
 	group_fds = kcalloc(hdr->count, sizeof(*group_fds), GFP_KERNEL);
@@ -1326,7 +1327,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev,
 	info.count = hdr->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--)
@@ -1341,6 +1342,7 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev,
 {
 	unsigned long minsz = offsetofend(struct vfio_pci_hot_reset, count);
 	struct vfio_pci_hot_reset hdr;
+	struct iommufd_ctx *iommufd;
 	bool slot = false;
 
 	if (copy_from_user(&hdr, arg, minsz))
@@ -1355,7 +1357,12 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev,
 	else if (pci_probe_reset_bus(vdev->pdev->bus))
 		return -ENODEV;
 
-	return vfio_pci_ioctl_pci_hot_reset_groups(vdev, &hdr, slot, arg);
+	if (hdr.count)
+		return vfio_pci_ioctl_pci_hot_reset_groups(vdev, &hdr, slot, arg);
+
+	iommufd = vfio_iommufd_physical_ictx(&vdev->vdev);
+
+	return vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, NULL, iommufd);
 }
 
 static int vfio_pci_ioctl_ioeventfd(struct vfio_pci_core_device *vdev,
@@ -2327,6 +2334,9 @@ static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev,
 {
 	unsigned int i;
 
+	if (!groups)
+		return false;
+
 	for (i = 0; i < groups->count; i++)
 		if (vfio_file_has_dev(groups->files[i], &vdev->vdev))
 			return true;
@@ -2402,13 +2412,25 @@ static int vfio_pci_dev_set_pm_runtime_get(struct vfio_device_set *dev_set)
 	return ret;
 }
 
+static bool vfio_dev_in_iommufd_ctx(struct vfio_pci_core_device *vdev,
+				    struct iommufd_ctx *iommufd_ctx)
+{
+	struct iommufd_ctx *iommufd = vfio_iommufd_physical_ictx(&vdev->vdev);
+
+	if (!iommufd)
+		return false;
+
+	return iommufd == iommufd_ctx;
+}
+
 /*
  * We need to get memory_lock for each device, but devices can share mmap_lock,
  * therefore we need to zap and hold the vma_lock for each device, and only then
  * 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;
@@ -2448,9 +2470,17 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
 		 *
 		 * Otherwise all opened devices in the dev_set must be
 		 * contained by the set of groups provided by the user.
+		 *
+		 * If user provides a zero-length array, then all the
+		 * opened devices must be bound to a same iommufd_ctx.
+		 *
+		 * If all above checks are failed, reset is allowed only if
+		 * the calling device is in a singleton dev_set.
 		 */
 		if (cur_vma->vdev.open_count &&
-		    !vfio_dev_in_groups(cur_vma, groups)) {
+		    !vfio_dev_in_groups(cur_vma, groups) &&
+		    !vfio_dev_in_iommufd_ctx(cur_vma, iommufd_ctx) &&
+		    (dev_set->device_count > 1)) {
 			ret = -EINVAL;
 			goto err_undo;
 		}
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index f96e5689cffc..17aa5d09db41 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -679,7 +679,14 @@ struct vfio_pci_hot_reset_info {
  * the calling user must ensure all affected devices, if opened, are
  * owned by itself.
  *
- * The ownership is proved by an array of group fds.
+ * The ownership can be proved by:
+ *   - An array of group fds
+ *   - A zero-length array
+ *
+ * In the last case all affected devices which are opened by this user
+ * must have been bound to a same iommufd. If the calling device is in
+ * noiommu mode (no valid iommufd) then it can be reset only if the reset
+ * doesn't affect other devices.
  *
  * Return: 0 on success, -errno on failure.
  */
-- 
2.34.1