Module Name: src
Committed By: riastradh
Date: Fri Aug 12 10:49:58 UTC 2022
Modified Files:
src/sys/dev/pci: virtio.c
Log Message:
virtio(4): Membar and bus_dmamap_sync audit.
- Don't use membar_* for DMA.
- Sync only the header and payload of the rings separately as needed.
If we bounce, this avoids large memcpy when we only care about the
header.
- Sync uring with PREREAD before triggering anything that will return
data in it.
=> Move uring PREREAD in virtio_enqueue_commit to _before_ updating
vq->vq_avail->idx, which is the pointat which the DMA read is
triggered in the `device' (host).
=> Omit needless membar_consumer in virtio_enqueue_commit -- may not
work with DMA memory, and even if it does, redundant with
bus_dmamap_sync uring PREREAD here.
=> XXX Does the device/host ever return unsolicited entries in the
queue, or only solicited ones? If only solicited ones, the
PREREAD in virtio_init_vq is redundant.
- Sync uring with POSTREAD before we read from it. This way the DMA
read into our buffer has finished before we read from the buffer.
=> Add missing uring POSTREAD in virtio_vq_is_enqueued, between read of
vq->vq_used_idx and return to caller, so that the caller can
safely use virtio_dequeue.
=> Add missing uring POSTREADs in virtio_start_vq_intr:
. between entry from caller and the read of vq->vq_used_idx
. between the read of vq->vq_used_idx and return to caller,
so that the caller can safely use virtio_dequeue, just like
virtio_vq_is_enqueued
=> Move uring POSTREADs in virtio_enqueue_commit to _before_ reading
vq->vq_used->flags or *vq->vq_avail_event, not after.
- After we write to aring, sync it with PREWRITE. This way we finish
writing to our buffer before the DMA write from it.
=> Omit needless PREWRITE in virtio_init_vq -- we do the appropriate
PREWRITE in virtio_enqueue_commit now.
=> Convert membar_producer to bus_dmamap_sync PREWRITE in
virtio_enqueue_commit.
=> Omit incorrect aring POSTWRITE in virtio_enqueue_commit -- no need
because the DMA write may not have completed yet at this point,
and we already do a POSTWRITE in virtio_vq_is_enqueued.
=> Omit needless membar_producer in virtio_postpone_intr -- may not
work with DMA memory, and even if it does, redundant with
bus_dmamap_sync PREWRITE here.
- After xfers to aring have completed, sync it with POSTWRITE.
=> Add missing aring POSTWRITE in virtio_free_vq, in case there are
paths from virtio_enqueue_commit to here that don't go through
virtio_is_enqueued. (If there are no such paths, then maybe we
should KASSERT(vq->vq_queued == 0) in virtio_free_vq.)
To generate a diff of this commit:
cvs rdiff -u -r1.56 -r1.57 src/sys/dev/pci/virtio.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
