On Thu, Oct 12, 2023 at 05:10:50PM +0200, Matias Ezequiel Vara Larsen wrote: > This commit replaces the mmap mechanism with the copy() and > fill_silence() callbacks for both capturing and playback for the > virtio-sound driver. This change is required to prevent the updating of > the content of a buffer that is already in the available ring. > > The current mechanism splits a dma buffer into descriptors that are > exposed to the device. This dma buffer is shared with the user > application. When the device consumes a buffer, the driver moves the > request from the used ring to available ring. > > The driver exposes the buffer to the device without knowing if the > content has been updated from the user. The section 2.8.21.1 of the > virtio spec states that: "The device MAY access the descriptor chains > the driver created and the memory they refer to immediately". If the > device picks up buffers from the available ring just after it is > notified, it happens that the content may be old. > > By providing the copy() callback, the driver first updates the content > of the buffer, and then, exposes the buffer to the device by enqueuing > it in the available ring. Thus, device always picks up a buffer that is > updated. > > For capturing, the driver starts by exposing all the available buffers > to device. After device updates the content of a buffer, it enqueues it > in the used ring. It is only after the copy() for capturing is issued > that the driver re-enqueues the buffer in the available ring. > > Note that the copy() function assumes that user is always writing a > period. Testing shows that this is true but I may be wrong. This RFC > aims at clarifying this. > > Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@xxxxxxxxxx> Thank you for working on this! > --- > sound/virtio/virtio_pcm.c | 11 ++-- > sound/virtio/virtio_pcm.h | 9 +++- > sound/virtio/virtio_pcm_msg.c | 50 ++++++++++++++++--- > sound/virtio/virtio_pcm_ops.c | 94 +++++++++++++++++++++++++++++++---- > 4 files changed, 137 insertions(+), 27 deletions(-) > > diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c > index c10d91fff2fb..bfe982952303 100644 > --- a/sound/virtio/virtio_pcm.c > +++ b/sound/virtio/virtio_pcm.c > @@ -104,8 +104,6 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss, > * only message-based transport. > */ > vss->hw.info = > - SNDRV_PCM_INFO_MMAP | > - SNDRV_PCM_INFO_MMAP_VALID | > SNDRV_PCM_INFO_BATCH | > SNDRV_PCM_INFO_BLOCK_TRANSFER | > SNDRV_PCM_INFO_INTERLEAVED | > @@ -471,12 +469,11 @@ int virtsnd_pcm_build_devs(struct virtio_snd *snd) > for (kss = ks->substream; kss; kss = kss->next) > vs->substreams[kss->number]->substream = kss; > > - snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_ops); > + if (i == SNDRV_PCM_STREAM_CAPTURE) > + snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_capture_ops); > + else > + snd_pcm_set_ops(vpcm->pcm, i, &virtsnd_pcm_playback_ops); > } > - > - snd_pcm_set_managed_buffer_all(vpcm->pcm, > - SNDRV_DMA_TYPE_VMALLOC, NULL, > - 0, 0); > } > > return 0; > diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h > index 062eb8e8f2cf..1c1106ec971f 100644 > --- a/sound/virtio/virtio_pcm.h > +++ b/sound/virtio/virtio_pcm.h > @@ -50,6 +50,8 @@ struct virtio_pcm_substream { > struct work_struct elapsed_period; > spinlock_t lock; > size_t buffer_bytes; > + u8 *buffer; > + size_t buffer_sz; > size_t hw_ptr; > bool xfer_enabled; > bool xfer_xrun; > @@ -90,7 +92,8 @@ struct virtio_pcm { > struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1]; > }; > > -extern const struct snd_pcm_ops virtsnd_pcm_ops; > +extern const struct snd_pcm_ops virtsnd_pcm_playback_ops; > +extern const struct snd_pcm_ops virtsnd_pcm_capture_ops; > > int virtsnd_pcm_validate(struct virtio_device *vdev); > > @@ -117,7 +120,9 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss, > > void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss); > > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss); > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single); > + > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single); > > unsigned int virtsnd_pcm_msg_pending_num(struct virtio_pcm_substream *vss); > > diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c > index aca2dc1989ba..9a5f9814cb62 100644 > --- a/sound/virtio/virtio_pcm_msg.c > +++ b/sound/virtio/virtio_pcm_msg.c > @@ -132,7 +132,6 @@ static void virtsnd_pcm_sg_from(struct scatterlist *sgs, int nsgs, u8 *data, > int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss, > unsigned int periods, unsigned int period_bytes) > { > - struct snd_pcm_runtime *runtime = vss->substream->runtime; > unsigned int i; > > vss->msgs = kcalloc(periods, sizeof(*vss->msgs), GFP_KERNEL); > @@ -142,7 +141,7 @@ int virtsnd_pcm_msg_alloc(struct virtio_pcm_substream *vss, > vss->nmsgs = periods; > > for (i = 0; i < periods; ++i) { > - u8 *data = runtime->dma_area + period_bytes * i; > + u8 *data = vss->buffer + period_bytes * i; > int sg_num = virtsnd_pcm_sg_num(data, period_bytes); > struct virtio_pcm_msg *msg; > > @@ -186,10 +185,12 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss) > /** > * virtsnd_pcm_msg_send() - Send asynchronous I/O messages. > * @vss: VirtIO PCM substream. > + * @single: true to enqueue a single message, false to enqueue all of them. > * > * All messages are organized in an ordered circular list. Each time the > - * function is called, all currently non-enqueued messages are added to the > - * virtqueue. For this, the function keeps track of two values: > + * function is called, first non-enqueued message is added to the virtqueue. > + * When single is True, only the first message is enqueued. When False, all the > + * available messages are enqueued. The function keeps track of two values: > * > * msg_last_enqueued = index of the last enqueued message, > * msg_count = # of pending messages in the virtqueue. > @@ -198,7 +199,7 @@ void virtsnd_pcm_msg_free(struct virtio_pcm_substream *vss) > * spinlocks to be held by caller. > * Return: 0 on success, -errno on failure. > */ > -int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss) > +int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss, bool single) > { > struct snd_pcm_runtime *runtime = vss->substream->runtime; > struct virtio_snd *snd = vss->snd; > @@ -211,6 +212,13 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss) > i = (vss->msg_last_enqueued + 1) % runtime->periods; > n = runtime->periods - vss->msg_count; > > + if (single) { > + if (n < 1) > + return -EFAULT; > + > + n = 1; > + } > + > for (; n; --n, i = (i + 1) % runtime->periods) { > struct virtio_pcm_msg *msg = vss->msgs[i]; > struct scatterlist *psgs[] = { > @@ -250,6 +258,36 @@ int virtsnd_pcm_msg_send(struct virtio_pcm_substream *vss) > return 0; > } > > +/** > + * virtsnd_pcm_msg_send_locked() - Send asynchronous I/O messages. > + * @vss: VirtIO PCM substream. > + * @single: true to enqueue a single message, false to enqueue all of them. > + * > + * This function holds the tx/rx queue and the VirtIO substream spinlocks > + * before calling virtsnd_pcm_msg_send(). This is a wrapper function to ease > + * the invocation of virtsnd_pcm_msg_send(). > + * > + * Context: Any context. > + * Return: 0 on success, -errno on failure. > + */ > + > +int virtsnd_pcm_msg_send_locked(struct virtio_pcm_substream *vss, bool single) > +{ > + struct virtio_snd_queue *queue; > + int rc; > + unsigned long flags; > + > + queue = virtsnd_pcm_queue(vss); > + > + spin_lock_irqsave(&queue->lock, flags); > + spin_lock(&vss->lock); > + rc = virtsnd_pcm_msg_send(vss, single); > + spin_unlock(&vss->lock); > + spin_unlock_irqrestore(&queue->lock, flags); > + > + return rc; > +} > + > /** > * virtsnd_pcm_msg_pending_num() - Returns the number of pending I/O messages. > * @vss: VirtIO substream. > @@ -320,8 +358,6 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg, > le32_to_cpu(msg->status.latency_bytes)); > > schedule_work(&vss->elapsed_period); > - > - virtsnd_pcm_msg_send(vss); > } else if (!vss->msg_count) { > wake_up_all(&vss->msg_empty); > } > diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c > index f8bfb87624be..a208439dbff8 100644 > --- a/sound/virtio/virtio_pcm_ops.c > +++ b/sound/virtio/virtio_pcm_ops.c > @@ -238,6 +238,11 @@ static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream, > */ > virtsnd_pcm_msg_free(vss); > > + vss->buffer_sz = params_buffer_bytes(hw_params); > + vss->buffer = alloc_pages_exact(vss->buffer_sz, GFP_KERNEL); > + if (!vss->buffer) > + return -ENOMEM; > + > return virtsnd_pcm_msg_alloc(vss, params_periods(hw_params), > params_period_bytes(hw_params)); > } > @@ -257,6 +262,11 @@ static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream) > if (!virtsnd_pcm_msg_pending_num(vss)) > virtsnd_pcm_msg_free(vss); > > + if (vss->buffer) { > + free_pages_exact(vss->buffer, vss->buffer_sz); > + vss->buffer = NULL; > + } > + > return 0; > } > > @@ -331,15 +341,18 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command) > case SNDRV_PCM_TRIGGER_PAUSE_RELEASE: > queue = virtsnd_pcm_queue(vss); > > - spin_lock_irqsave(&queue->lock, flags); > - spin_lock(&vss->lock); > - rc = virtsnd_pcm_msg_send(vss); > - if (!rc) > - vss->xfer_enabled = true; > - spin_unlock(&vss->lock); > - spin_unlock_irqrestore(&queue->lock, flags); > - if (rc) > - return rc; > + // The buffers should be exposed first during capturing so that > + // the device can consume them. Capturing cannot begin > + // otherwise. > + if (vss->direction == SNDRV_PCM_STREAM_CAPTURE) { > + rc = virtsnd_pcm_msg_send_locked(vss, false); > + if (rc) > + return rc; > + } > + > + spin_lock_irqsave(&vss->lock, flags); > + vss->xfer_enabled = true; > + spin_unlock_irqrestore(&vss->lock, flags); > > msg = virtsnd_pcm_ctl_msg_alloc(vss, VIRTIO_SND_R_PCM_START, > GFP_KERNEL); > @@ -450,8 +463,66 @@ virtsnd_pcm_pointer(struct snd_pcm_substream *substream) > return hw_ptr; > } > > -/* PCM substream operators map. */ > -const struct snd_pcm_ops virtsnd_pcm_ops = { > +static int virtsnd_pcm_pb_copy(struct snd_pcm_substream *substream, > + int channel, unsigned long pos, struct iov_iter > + *src, unsigned long count) > +{ > + struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream); > + > + if (unlikely(pos + count > vss->buffer_sz)) > + return -EINVAL; > + > + if (copy_from_iter(vss->buffer + pos, count, src) != count) > + return -EFAULT; > + > + return virtsnd_pcm_msg_send_locked(vss, true); > +} > + > +static int virtsnd_pcm_cap_copy(struct snd_pcm_substream *substream, > + int channel, unsigned long pos, struct iov_iter > + *dst, unsigned long count) > +{ > + struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream); > + > + if (unlikely(pos + count > vss->buffer_sz)) > + return -EINVAL; > + > + if (copy_to_iter(vss->buffer + pos, count, dst) != count) > + return -EFAULT; > + > + return virtsnd_pcm_msg_send_locked(vss, true); > +} > + > +static int virtsnd_pcm_pb_silence(struct snd_pcm_substream *substream, int channel, > + unsigned long pos, unsigned long count) > +{ > + struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream); > + > + if (unlikely(pos + count > vss->buffer_sz)) > + return -EINVAL; > + > + memset(vss->buffer + pos, 0, count); > + > + return virtsnd_pcm_msg_send_locked(vss, true); > +} > + > +/* PCM substream operators map for playback. */ > +const struct snd_pcm_ops virtsnd_pcm_playback_ops = { > + .open = virtsnd_pcm_open, > + .close = virtsnd_pcm_close, > + .ioctl = snd_pcm_lib_ioctl, > + .hw_params = virtsnd_pcm_hw_params, > + .hw_free = virtsnd_pcm_hw_free, > + .prepare = virtsnd_pcm_prepare, > + .trigger = virtsnd_pcm_trigger, > + .sync_stop = virtsnd_pcm_sync_stop, > + .pointer = virtsnd_pcm_pointer, > + .copy = virtsnd_pcm_pb_copy, > + .fill_silence = virtsnd_pcm_pb_silence, > +}; > + > +/* PCM substream operators map for capturing. */ > +const struct snd_pcm_ops virtsnd_pcm_capture_ops = { > .open = virtsnd_pcm_open, > .close = virtsnd_pcm_close, > .ioctl = snd_pcm_lib_ioctl, > @@ -461,4 +532,5 @@ const struct snd_pcm_ops virtsnd_pcm_ops = { > .trigger = virtsnd_pcm_trigger, > .sync_stop = virtsnd_pcm_sync_stop, > .pointer = virtsnd_pcm_pointer, > + .copy = virtsnd_pcm_cap_copy, > }; > > base-commit: 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa > -- > 2.41.0