On Tue, Apr 17, 2018 at 10:11:58AM +0800, Jason Wang wrote:> On 2018?04?13? 15:15, Tiwei Bie wrote: > > On Fri, Apr 13, 2018 at 12:30:24PM +0800, Jason Wang wrote: > > > On 2018?04?01? 22:12, Tiwei Bie wrote:[...]> > > > +static int detach_buf_packed(struct vring_virtqueue *vq, unsigned int head, > > > > + void **ctx) > > > > +{ > > > > + struct vring_packed_desc *desc; > > > > + unsigned int i, j; > > > > + > > > > + /* Clear data ptr. */ > > > > + vq->desc_state[head].data = NULL; > > > > + > > > > + i = head; > > > > + > > > > + for (j = 0; j < vq->desc_state[head].num; j++) { > > > > + desc = &vq->vring_packed.desc[i]; > > > > + vring_unmap_one_packed(vq, desc); > > > > + desc->flags = 0x0; > > > Looks like this is unnecessary. > > It's safer to zero it. If we don't zero it, after we > > call virtqueue_detach_unused_buf_packed() which calls > > this function, the desc is still available to the > > device. > > Well detach_unused_buf_packed() should be called after device is stopped, > otherwise even if you try to clear, there will still be a window that device > may use it.This is not about whether the device has been stopped or not. We don't have other places to re-initialize the ring descriptors and wrap_counter. So they need to be set to the correct values when doing detach_unused_buf. Best regards, Tiwei Bie
On Tue, Apr 17, 2018 at 10:51:33AM +0800, Tiwei Bie wrote:> On Tue, Apr 17, 2018 at 10:11:58AM +0800, Jason Wang wrote: > > On 2018?04?13? 15:15, Tiwei Bie wrote: > > > On Fri, Apr 13, 2018 at 12:30:24PM +0800, Jason Wang wrote: > > > > On 2018?04?01? 22:12, Tiwei Bie wrote: > [...] > > > > > +static int detach_buf_packed(struct vring_virtqueue *vq, unsigned int head, > > > > > + void **ctx) > > > > > +{ > > > > > + struct vring_packed_desc *desc; > > > > > + unsigned int i, j; > > > > > + > > > > > + /* Clear data ptr. */ > > > > > + vq->desc_state[head].data = NULL; > > > > > + > > > > > + i = head; > > > > > + > > > > > + for (j = 0; j < vq->desc_state[head].num; j++) { > > > > > + desc = &vq->vring_packed.desc[i]; > > > > > + vring_unmap_one_packed(vq, desc); > > > > > + desc->flags = 0x0; > > > > Looks like this is unnecessary. > > > It's safer to zero it. If we don't zero it, after we > > > call virtqueue_detach_unused_buf_packed() which calls > > > this function, the desc is still available to the > > > device. > > > > Well detach_unused_buf_packed() should be called after device is stopped, > > otherwise even if you try to clear, there will still be a window that device > > may use it. > > This is not about whether the device has been stopped or > not. We don't have other places to re-initialize the ring > descriptors and wrap_counter. So they need to be set to > the correct values when doing detach_unused_buf. > > Best regards, > Tiwei Biefind vqs is the time to do it. -- MST
On Tue, Apr 17, 2018 at 03:17:41PM +0300, Michael S. Tsirkin wrote:> On Tue, Apr 17, 2018 at 10:51:33AM +0800, Tiwei Bie wrote: > > On Tue, Apr 17, 2018 at 10:11:58AM +0800, Jason Wang wrote: > > > On 2018?04?13? 15:15, Tiwei Bie wrote: > > > > On Fri, Apr 13, 2018 at 12:30:24PM +0800, Jason Wang wrote: > > > > > On 2018?04?01? 22:12, Tiwei Bie wrote: > > [...] > > > > > > +static int detach_buf_packed(struct vring_virtqueue *vq, unsigned int head, > > > > > > + void **ctx) > > > > > > +{ > > > > > > + struct vring_packed_desc *desc; > > > > > > + unsigned int i, j; > > > > > > + > > > > > > + /* Clear data ptr. */ > > > > > > + vq->desc_state[head].data = NULL; > > > > > > + > > > > > > + i = head; > > > > > > + > > > > > > + for (j = 0; j < vq->desc_state[head].num; j++) { > > > > > > + desc = &vq->vring_packed.desc[i]; > > > > > > + vring_unmap_one_packed(vq, desc); > > > > > > + desc->flags = 0x0; > > > > > Looks like this is unnecessary. > > > > It's safer to zero it. If we don't zero it, after we > > > > call virtqueue_detach_unused_buf_packed() which calls > > > > this function, the desc is still available to the > > > > device. > > > > > > Well detach_unused_buf_packed() should be called after device is stopped, > > > otherwise even if you try to clear, there will still be a window that device > > > may use it. > > > > This is not about whether the device has been stopped or > > not. We don't have other places to re-initialize the ring > > descriptors and wrap_counter. So they need to be set to > > the correct values when doing detach_unused_buf. > > > > Best regards, > > Tiwei Bie > > find vqs is the time to do it.The .find_vqs() will call .setup_vq() which will eventually call vring_create_virtqueue(). It's a different case. Here we're talking about re-initializing the descs and updating the wrap counter when detaching the unused descs (In this case, split ring just needs to decrease vring.avail->idx). Best regards, Tiwei Bie