On Thu, 29 Feb 2024 09:11:52 +0000 Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx> wrote: > 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@xxxxxxxxxx/ > Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx> > --- > .../vfio/pci/hisilicon/hisi_acc_vfio_pci.c | 48 +++++-------------- > .../vfio/pci/hisilicon/hisi_acc_vfio_pci.h | 6 +-- > 2 files changed, 14 insertions(+), 40 deletions(-) Applied to vfio next branch for v6.9. Thanks, Alex > > diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c > index 4d27465c8f1a..9a3e97108ace 100644 > --- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c > +++ b/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) > diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.h b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.h > index dcabfeec6ca1..5bab46602fad 100644 > --- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.h > +++ b/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; > };
