On Thu, Mar 03, 2022 at 12:57:29PM +0000, Shameerali Kolothum Thodi wrote: > > > > From: Jason Gunthorpe [mailto:jgg@xxxxxxxxxx] > > Sent: 03 March 2022 00:22 > > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> > > Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > linux-crypto@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; > > alex.williamson@xxxxxxxxxx; cohuck@xxxxxxxxxx; mgurtovoy@xxxxxxxxxx; > > yishaih@xxxxxxxxxx; Linuxarm <linuxarm@xxxxxxxxxx>; liulongfang > > <liulongfang@xxxxxxxxxx>; Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>; > > Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>; Wangzhou (B) > > <wangzhou1@xxxxxxxxxxxxx> > > Subject: Re: [PATCH v7 09/10] hisi_acc_vfio_pci: Add support for VFIO live > > migration > > > > On Wed, Mar 02, 2022 at 05:29:02PM +0000, Shameer Kolothum wrote: > > > +static long hisi_acc_vf_save_unl_ioctl(struct file *filp, > > > + unsigned int cmd, unsigned long arg) > > > +{ > > > + struct hisi_acc_vf_migration_file *migf = filp->private_data; > > > + struct hisi_acc_vf_core_device *hisi_acc_vdev = container_of(migf, > > > + struct hisi_acc_vf_core_device, saving_migf); > > > + loff_t *pos = &filp->f_pos; > > > + struct vfio_precopy_info info; > > > + unsigned long minsz; > > > + int ret; > > > + > > > + if (cmd != VFIO_MIG_GET_PRECOPY_INFO) > > > + return -ENOTTY; > > > + > > > + minsz = offsetofend(struct vfio_precopy_info, dirty_bytes); > > > + > > > + if (copy_from_user(&info, (void __user *)arg, minsz)) > > > + return -EFAULT; > > > + if (info.argsz < minsz) > > > + return -EINVAL; > > > + > > > + mutex_lock(&hisi_acc_vdev->state_mutex); > > > + if (hisi_acc_vdev->mig_state != VFIO_DEVICE_STATE_PRE_COPY) { > > > + mutex_unlock(&hisi_acc_vdev->state_mutex); > > > + return -EINVAL; > > > + } > > > > IMHO it is easier just to check the total_length and not grab this > > other lock > > The problem with checking the total_length here is that it is possible that > in STOP_COPY the dev is not ready and there are no more data to be transferred > and the total_length remains at QM_MATCH_SIZE. Tthere is a scenario that transfers only QM_MATCH_SIZE in stop_copy? This doesn't seem like a good idea, I think you should transfer a positive indication 'this device is not ready' instead of truncating the stream. A truncated stream should not be a valid stream. ie always transfer the whole struct. > Looks like setting the total_length = 0 in STOP_COPY is a better solution(If there are > no other issues with that) as it will avoid grabbing the state_mutex as you > mentioned above. That seems really weird, I wouldn't recommend doing that.. Kaspm
