Jason Wang
2021-Jun-02 09:50 UTC
[RFC v3 17/29] vhost: Shadow virtqueue buffers forwarding
? 2021/5/20 ??12:28, Eugenio P?rez ??:> Initial version of shadow virtqueue that actually forward buffers. The > exposed addresses are the qemu's virtual address, so devices with IOMMU > that does not allow full mapping of qemu's address space does not work > at the moment. > > Also for simplicity it only supports modern devices, that expects vring > in little endian, with split ring and no event idx or indirect > descriptors. > > It reuses the VirtQueue code for the device part. The driver part is > based on Linux's virtio_ring driver, but with stripped functionality > and optimizations so it's easier to review. > > Later commits will solve some of these concerns.It would be more more easier to review if you squash those "enhancements" into this patch.> > Code also need to map used ring (device part) as RW in, and only in, > vhost-net. To map (or call vhost_device_iotlb_miss) inconditionally > would print an error in case of vhost devices with its own mapping > (vdpa).I think we should not depend on the IOTLB miss. Instead, we should program the device IOTLB before starting the svq. Or is there anything that prevent you from doing this?> To know if this call is needed, vhost_sw_live_migration_start_vq and > vhost_sw_live_migration_stop copy the test performed in > vhost_dev_start. Testing for the actual backend type could be cleaner, > or checking for non-NULL vhost_force_iommu, enable_custom_iommu, or > another vhostOp. We could extract this test in its own function too, > so its name could give a better hint. Just copy the vhost_dev_start > check at the moment. > > Signed-off-by: Eugenio P?rez <eperezma at redhat.com> > --- > hw/virtio/vhost-shadow-virtqueue.c | 205 +++++++++++++++++++++++++++-- > hw/virtio/vhost.c | 134 ++++++++++++++++++- > 2 files changed, 325 insertions(+), 14 deletions(-) > > diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c > index ff50f12410..6d767fe248 100644 > --- a/hw/virtio/vhost-shadow-virtqueue.c > +++ b/hw/virtio/vhost-shadow-virtqueue.c > @@ -9,6 +9,7 @@ > > #include "hw/virtio/vhost-shadow-virtqueue.h" > #include "hw/virtio/vhost.h" > +#include "hw/virtio/virtio-access.h" > > #include "standard-headers/linux/vhost_types.h" > > @@ -48,9 +49,93 @@ typedef struct VhostShadowVirtqueue { > > /* Virtio device */ > VirtIODevice *vdev; > + > + /* Map for returning guest's descriptors */ > + VirtQueueElement **ring_id_maps; > + > + /* Next head to expose to device */ > + uint16_t avail_idx_shadow; > + > + /* Next free descriptor */ > + uint16_t free_head; > + > + /* Last seen used idx */ > + uint16_t shadow_used_idx; > + > + /* Next head to consume from device */ > + uint16_t used_idx; > } VhostShadowVirtqueue; > > -/* Forward guest notifications */ > +static void vhost_vring_write_descs(VhostShadowVirtqueue *svq, > + const struct iovec *iovec, > + size_t num, bool more_descs, bool write) > +{ > + uint16_t i = svq->free_head, last = svq->free_head; > + unsigned n; > + uint16_t flags = write ? cpu_to_le16(VRING_DESC_F_WRITE) : 0; > + vring_desc_t *descs = svq->vring.desc; > + > + if (num == 0) { > + return; > + } > + > + for (n = 0; n < num; n++) { > + if (more_descs || (n + 1 < num)) { > + descs[i].flags = flags | cpu_to_le16(VRING_DESC_F_NEXT); > + } else { > + descs[i].flags = flags; > + } > + descs[i].addr = cpu_to_le64((hwaddr)iovec[n].iov_base); > + descs[i].len = cpu_to_le32(iovec[n].iov_len); > + > + last = i; > + i = cpu_to_le16(descs[i].next); > + } > + > + svq->free_head = le16_to_cpu(descs[last].next); > +} > + > +static unsigned vhost_shadow_vq_add_split(VhostShadowVirtqueue *svq, > + VirtQueueElement *elem) > +{ > + int head; > + unsigned avail_idx; > + vring_avail_t *avail = svq->vring.avail; > + > + head = svq->free_head; > + > + /* We need some descriptors here */ > + assert(elem->out_num || elem->in_num); > + > + vhost_vring_write_descs(svq, elem->out_sg, elem->out_num, > + elem->in_num > 0, false); > + vhost_vring_write_descs(svq, elem->in_sg, elem->in_num, false, true); > + > + /* > + * Put entry in available array (but don't update avail->idx until they > + * do sync). > + */ > + avail_idx = svq->avail_idx_shadow & (svq->vring.num - 1); > + avail->ring[avail_idx] = cpu_to_le16(head); > + svq->avail_idx_shadow++; > + > + /* Expose descriptors to device */It's better to describe the detail order. E.g "Update avail index after the descriptor is wrote"> + smp_wmb(); > + avail->idx = cpu_to_le16(svq->avail_idx_shadow); > + > + return head; > + > +} > + > +static void vhost_shadow_vq_add(VhostShadowVirtqueue *svq, > + VirtQueueElement *elem) > +{ > + unsigned qemu_head = vhost_shadow_vq_add_split(svq, elem); > + > + svq->ring_id_maps[qemu_head] = elem; > +} > + > +/* Handle guest->device notifications */ > static void vhost_handle_guest_kick(EventNotifier *n) > { > VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue, > @@ -60,7 +145,67 @@ static void vhost_handle_guest_kick(EventNotifier *n) > return; > } > > - event_notifier_set(&svq->kick_notifier); > + /* Make available as many buffers as possible */ > + do { > + if (virtio_queue_get_notification(svq->vq)) { > + /* No more notifications until process all available */ > + virtio_queue_set_notification(svq->vq, false); > + } > + > + while (true) { > + VirtQueueElement *elem = virtqueue_pop(svq->vq, sizeof(*elem)); > + if (!elem) { > + break; > + } > + > + vhost_shadow_vq_add(svq, elem); > + event_notifier_set(&svq->kick_notifier); > + } > + > + virtio_queue_set_notification(svq->vq, true); > + } while (!virtio_queue_empty(svq->vq)); > +} > + > +static bool vhost_shadow_vq_more_used(VhostShadowVirtqueue *svq) > +{ > + if (svq->used_idx != svq->shadow_used_idx) { > + return true; > + } > + > + /* Get used idx must not be reordered */ > + smp_rmb(); > + svq->shadow_used_idx = cpu_to_le16(svq->vring.used->idx); > + > + return svq->used_idx != svq->shadow_used_idx; > +} > + > +static VirtQueueElement *vhost_shadow_vq_get_buf(VhostShadowVirtqueue *svq) > +{ > + vring_desc_t *descs = svq->vring.desc; > + const vring_used_t *used = svq->vring.used; > + vring_used_elem_t used_elem; > + uint16_t last_used; > + > + if (!vhost_shadow_vq_more_used(svq)) { > + return NULL; > + } > + > + last_used = svq->used_idx & (svq->vring.num - 1); > + used_elem.id = le32_to_cpu(used->ring[last_used].id); > + used_elem.len = le32_to_cpu(used->ring[last_used].len); > + > + if (unlikely(used_elem.id >= svq->vring.num)) { > + error_report("Device %s says index %u is available", svq->vdev->name, > + used_elem.id); > + return NULL; > + } > + > + descs[used_elem.id].next = svq->free_head; > + svq->free_head = used_elem.id; > + > + svq->used_idx++; > + svq->ring_id_maps[used_elem.id]->len = used_elem.len; > + return g_steal_pointer(&svq->ring_id_maps[used_elem.id]); > } > > /* Forward vhost notifications */ > @@ -69,17 +214,33 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n) > VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue, > call_notifier); > EventNotifier *masked_notifier; > + VirtQueue *vq = svq->vq; > > masked_notifier = svq->masked_notifier.n; > > - if (!masked_notifier) { > - unsigned n = virtio_get_queue_index(svq->vq); > - virtio_queue_invalidate_signalled_used(svq->vdev, n); > - virtio_notify_irqfd(svq->vdev, svq->vq); > - } else if (!svq->masked_notifier.signaled) { > - svq->masked_notifier.signaled = true; > - event_notifier_set(svq->masked_notifier.n); > - } > + /* Make as many buffers as possible used. */ > + do { > + unsigned i = 0; > + > + /* TODO: Use VRING_AVAIL_F_NO_INTERRUPT */ > + while (true) { > + g_autofree VirtQueueElement *elem = vhost_shadow_vq_get_buf(svq); > + if (!elem) { > + break; > + } > + > + assert(i < svq->vring.num); > + virtqueue_fill(vq, elem, elem->len, i++); > + } > + > + virtqueue_flush(vq, i); > + if (!masked_notifier) { > + virtio_notify_irqfd(svq->vdev, svq->vq);Any reason that you don't use virtio_notify() here?> + } else if (!svq->masked_notifier.signaled) { > + svq->masked_notifier.signaled = true; > + event_notifier_set(svq->masked_notifier.n); > + }This is an example of the extra complexity if you do shadow virtqueue at virtio level. If you do everything at e.g vhost-vdpa, you don't need to care about masked_notifer at all. Thanks