On Mon, Oct 04, 2021 at 09:38:04PM +0200, Christian Schoenebeck wrote: > Refactor VIRTQUEUE_MAX_SIZE to effectively become a runtime > variable per virtio user.
virtio user == virtio device model? > > Reasons: > > (1) VIRTQUEUE_MAX_SIZE should reflect the absolute theoretical > maximum queue size possible. Which is actually the maximum > queue size allowed by the virtio protocol. The appropriate > value for VIRTQUEUE_MAX_SIZE would therefore be 32768: > > > https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-240006 > > Apparently VIRTQUEUE_MAX_SIZE was instead defined with a > more or less arbitrary value of 1024 in the past, which > limits the maximum transfer size with virtio to 4M > (more precise: 1024 * PAGE_SIZE, with the latter typically > being 4k). Being equal to IOV_MAX is a likely reason. Buffers with more iovecs than that cannot be passed to host system calls (sendmsg(2), pwritev(2), etc). > (2) Additionally the current value of 1024 poses a hidden limit, > invisible to guest, which causes a system hang with the > following QEMU error if guest tries to exceed it: > > virtio: too many write descriptors in indirect table I don't understand this point. 2.6.5 The Virtqueue Descriptor Table says: The number of descriptors in the table is defined by the queue size for this virtqueue: this is the maximum possible descriptor chain length. and 2.6.5.3.1 Driver Requirements: Indirect Descriptors says: A driver MUST NOT create a descriptor chain longer than the Queue Size of the device. Do you mean a broken/malicious guest driver that is violating the spec? That's not a hidden limit, it's defined by the spec. > (3) Unfortunately not all virtio users in QEMU would currently > work correctly with the new value of 32768. > > So let's turn this hard coded global value into a runtime > variable as a first step in this commit, configurable for each > virtio user by passing a corresponding value with virtio_init() > call. virtio_add_queue() already has an int queue_size argument, why isn't that enough to deal with the maximum queue size? There's probably a good reason for it, but please include it in the commit description. > > Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com> > --- > hw/9pfs/virtio-9p-device.c | 3 ++- > hw/block/vhost-user-blk.c | 2 +- > hw/block/virtio-blk.c | 3 ++- > hw/char/virtio-serial-bus.c | 2 +- > hw/display/virtio-gpu-base.c | 2 +- > hw/input/virtio-input.c | 2 +- > hw/net/virtio-net.c | 15 ++++++++------- > hw/scsi/virtio-scsi.c | 2 +- > hw/virtio/vhost-user-fs.c | 2 +- > hw/virtio/vhost-user-i2c.c | 3 ++- > hw/virtio/vhost-vsock-common.c | 2 +- > hw/virtio/virtio-balloon.c | 4 ++-- > hw/virtio/virtio-crypto.c | 3 ++- > hw/virtio/virtio-iommu.c | 2 +- > hw/virtio/virtio-mem.c | 2 +- > hw/virtio/virtio-pmem.c | 2 +- > hw/virtio/virtio-rng.c | 2 +- > hw/virtio/virtio.c | 35 +++++++++++++++++++++++----------- > include/hw/virtio/virtio.h | 5 ++++- > 19 files changed, 57 insertions(+), 36 deletions(-) > > diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c > index 54ee93b71f..cd5d95dd51 100644 > --- a/hw/9pfs/virtio-9p-device.c > +++ b/hw/9pfs/virtio-9p-device.c > @@ -216,7 +216,8 @@ static void virtio_9p_device_realize(DeviceState *dev, > Error **errp) > } > > v->config_size = sizeof(struct virtio_9p_config) + strlen(s->fsconf.tag); > - virtio_init(vdev, "virtio-9p", VIRTIO_ID_9P, v->config_size); > + virtio_init(vdev, "virtio-9p", VIRTIO_ID_9P, v->config_size, > + VIRTQUEUE_MAX_SIZE); > v->vq = virtio_add_queue(vdev, MAX_REQ, handle_9p_output); > } > > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c > index ba13cb87e5..336f56705c 100644 > --- a/hw/block/vhost-user-blk.c > +++ b/hw/block/vhost-user-blk.c > @@ -491,7 +491,7 @@ static void vhost_user_blk_device_realize(DeviceState > *dev, Error **errp) > } > > virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, > - sizeof(struct virtio_blk_config)); > + sizeof(struct virtio_blk_config), VIRTQUEUE_MAX_SIZE); > > s->virtqs = g_new(VirtQueue *, s->num_queues); > for (i = 0; i < s->num_queues; i++) { > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c > index f139cd7cc9..9c0f46815c 100644 > --- a/hw/block/virtio-blk.c > +++ b/hw/block/virtio-blk.c > @@ -1213,7 +1213,8 @@ static void virtio_blk_device_realize(DeviceState *dev, > Error **errp) > > virtio_blk_set_config_size(s, s->host_features); > > - virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, s->config_size); > + virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, s->config_size, > + VIRTQUEUE_MAX_SIZE); > > s->blk = conf->conf.blk; > s->rq = NULL; > diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c > index f01ec2137c..9ad9111115 100644 > --- a/hw/char/virtio-serial-bus.c > +++ b/hw/char/virtio-serial-bus.c > @@ -1045,7 +1045,7 @@ static void virtio_serial_device_realize(DeviceState > *dev, Error **errp) > config_size = offsetof(struct virtio_console_config, emerg_wr); > } > virtio_init(vdev, "virtio-serial", VIRTIO_ID_CONSOLE, > - config_size); > + config_size, VIRTQUEUE_MAX_SIZE); > > /* Spawn a new virtio-serial bus on which the ports will ride as devices > */ > qbus_init(&vser->bus, sizeof(vser->bus), TYPE_VIRTIO_SERIAL_BUS, > diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c > index c8da4806e0..20b06a7adf 100644 > --- a/hw/display/virtio-gpu-base.c > +++ b/hw/display/virtio-gpu-base.c > @@ -171,7 +171,7 @@ virtio_gpu_base_device_realize(DeviceState *qdev, > > g->virtio_config.num_scanouts = cpu_to_le32(g->conf.max_outputs); > virtio_init(VIRTIO_DEVICE(g), "virtio-gpu", VIRTIO_ID_GPU, > - sizeof(struct virtio_gpu_config)); > + sizeof(struct virtio_gpu_config), VIRTQUEUE_MAX_SIZE); > > if (virtio_gpu_virgl_enabled(g->conf)) { > /* use larger control queue in 3d mode */ > diff --git a/hw/input/virtio-input.c b/hw/input/virtio-input.c > index 54bcb46c74..345eb2cce7 100644 > --- a/hw/input/virtio-input.c > +++ b/hw/input/virtio-input.c > @@ -258,7 +258,7 @@ static void virtio_input_device_realize(DeviceState *dev, > Error **errp) > assert(vinput->cfg_size <= sizeof(virtio_input_config)); > > virtio_init(vdev, "virtio-input", VIRTIO_ID_INPUT, > - vinput->cfg_size); > + vinput->cfg_size, VIRTQUEUE_MAX_SIZE); > vinput->evt = virtio_add_queue(vdev, 64, virtio_input_handle_evt); > vinput->sts = virtio_add_queue(vdev, 64, virtio_input_handle_sts); > } > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > index f205331dcf..f74b5f6268 100644 > --- a/hw/net/virtio-net.c > +++ b/hw/net/virtio-net.c > @@ -1746,9 +1746,9 @@ static ssize_t virtio_net_receive_rcu(NetClientState > *nc, const uint8_t *buf, > VirtIONet *n = qemu_get_nic_opaque(nc); > VirtIONetQueue *q = virtio_net_get_subqueue(nc); > VirtIODevice *vdev = VIRTIO_DEVICE(n); > - VirtQueueElement *elems[VIRTQUEUE_MAX_SIZE]; > - size_t lens[VIRTQUEUE_MAX_SIZE]; > - struct iovec mhdr_sg[VIRTQUEUE_MAX_SIZE]; > + VirtQueueElement *elems[vdev->queue_max_size]; > + size_t lens[vdev->queue_max_size]; > + struct iovec mhdr_sg[vdev->queue_max_size]; Can you make this value per-vq instead of per-vdev since virtqueues can have different queue sizes? The same applies to the rest of this patch. Anything using vdev->queue_max_size should probably use vq->vring.num instead.
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