hisi_acc_vfio_pci: Remove the deferred_reset logic

The deferred_reset logic was added to vfio migration drivers to prevent
a circular locking dependency with respect to mm_lock and state mutex.
This is mainly because of the copy_to/from_user() functions(which takes
mm_lock) invoked under state mutex. But for HiSilicon driver, the only
place where we now hold the state mutex for copy_to_user is during the
PRE_COPY IOCTL. So for pre_copy, release the lock as soon as we have
updated the data and perform copy_to_user without state mutex. By this,
we can get rid of the deferred_reset logic.

Link: https://lore.kernel.org/kvm/20240220132459.GM13330@nvidia.com/Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20240229091152.56664-1-shameerali.kolothum.thodi@huawei.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c

@@ -630,25 +630,11 @@ static void hisi_acc_vf_disable_fds(struct hisi_acc_vf_core_device *hisi_acc_vde
 	}
 }
 
-/*
- * This function is called in all state_mutex unlock cases to
- * handle a 'deferred_reset' if exists.
- */
-static void
-hisi_acc_vf_state_mutex_unlock(struct hisi_acc_vf_core_device *hisi_acc_vdev)
+static void hisi_acc_vf_reset(struct hisi_acc_vf_core_device *hisi_acc_vdev)
 {
-again:
-	spin_lock(&hisi_acc_vdev->reset_lock);
-	if (hisi_acc_vdev->deferred_reset) {
-		hisi_acc_vdev->deferred_reset = false;
-		spin_unlock(&hisi_acc_vdev->reset_lock);
-		hisi_acc_vdev->vf_qm_state = QM_NOT_READY;
-		hisi_acc_vdev->mig_state = VFIO_DEVICE_STATE_RUNNING;
-		hisi_acc_vf_disable_fds(hisi_acc_vdev);
-		goto again;
-	}
-	mutex_unlock(&hisi_acc_vdev->state_mutex);
-	spin_unlock(&hisi_acc_vdev->reset_lock);
+	hisi_acc_vdev->vf_qm_state = QM_NOT_READY;
+	hisi_acc_vdev->mig_state = VFIO_DEVICE_STATE_RUNNING;
+	hisi_acc_vf_disable_fds(hisi_acc_vdev);
 }
 
 static void hisi_acc_vf_start_device(struct hisi_acc_vf_core_device *hisi_acc_vdev)
@@ -804,8 +790,10 @@ static long hisi_acc_vf_precopy_ioctl(struct file *filp,
 
 	info.dirty_bytes = 0;
 	info.initial_bytes = migf->total_length - *pos;
+	mutex_unlock(&migf->lock);
+	mutex_unlock(&hisi_acc_vdev->state_mutex);
 
-	ret = copy_to_user((void __user *)arg, &info, minsz) ? -EFAULT : 0;
+	return copy_to_user((void __user *)arg, &info, minsz) ? -EFAULT : 0;
 out:
 	mutex_unlock(&migf->lock);
 	mutex_unlock(&hisi_acc_vdev->state_mutex);
@@ -1071,7 +1059,7 @@ hisi_acc_vfio_pci_set_device_state(struct vfio_device *vdev,
 			break;
 		}
 	}
-	hisi_acc_vf_state_mutex_unlock(hisi_acc_vdev);
+	mutex_unlock(&hisi_acc_vdev->state_mutex);
 	return res;
 }
 
@@ -1092,7 +1080,7 @@ hisi_acc_vfio_pci_get_device_state(struct vfio_device *vdev,
 
 	mutex_lock(&hisi_acc_vdev->state_mutex);
 	*curr_state = hisi_acc_vdev->mig_state;
-	hisi_acc_vf_state_mutex_unlock(hisi_acc_vdev);
+	mutex_unlock(&hisi_acc_vdev->state_mutex);
 	return 0;
 }
 
@@ -1104,21 +1092,9 @@ static void hisi_acc_vf_pci_aer_reset_done(struct pci_dev *pdev)
 				VFIO_MIGRATION_STOP_COPY)
 		return;
 
-	/*
-	 * As the higher VFIO layers are holding locks across reset and using
-	 * those same locks with the mm_lock we need to prevent ABBA deadlock
-	 * with the state_mutex and mm_lock.
-	 * In case the state_mutex was taken already we defer the cleanup work
-	 * to the unlock flow of the other running context.
-	 */
-	spin_lock(&hisi_acc_vdev->reset_lock);
-	hisi_acc_vdev->deferred_reset = true;
-	if (!mutex_trylock(&hisi_acc_vdev->state_mutex)) {
-		spin_unlock(&hisi_acc_vdev->reset_lock);
-		return;
-	}
-	spin_unlock(&hisi_acc_vdev->reset_lock);
-	hisi_acc_vf_state_mutex_unlock(hisi_acc_vdev);
+	mutex_lock(&hisi_acc_vdev->state_mutex);
+	hisi_acc_vf_reset(hisi_acc_vdev);
+	mutex_unlock(&hisi_acc_vdev->state_mutex);
 }
 
 static int hisi_acc_vf_qm_init(struct hisi_acc_vf_core_device *hisi_acc_vdev)

drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.h

@@ -98,8 +98,8 @@ struct hisi_acc_vf_migration_file {
 
 struct hisi_acc_vf_core_device {
 	struct vfio_pci_core_device core_device;
-	u8 match_done:1;
-	u8 deferred_reset:1;
+	u8 match_done;
+
 	/* For migration state */
 	struct mutex state_mutex;
 	enum vfio_device_mig_state mig_state;
@@ -109,8 +109,6 @@ struct hisi_acc_vf_core_device {
 	struct hisi_qm vf_qm;
 	u32 vf_qm_state;
 	int vf_id;
-	/* For reset handler */
-	spinlock_t reset_lock;
 	struct hisi_acc_vf_migration_file *resuming_migf;
 	struct hisi_acc_vf_migration_file *saving_migf;
 };