On Tue, Nov 30, 2021 at 06:40:49PM -0500, Michael S. Tsirkin wrote: > On Tue, Nov 30, 2021 at 01:45:10PM +0000, Stefan Hajnoczi wrote: > > Packed Virtqueues wrap used_idx instead of letting it run freely like > > Split Virtqueues do. If the used ring wraps more than once there is no > > way to compare vq->signalled_used and vq->used_idx in > > virtio_packed_should_notify() since they are modulo vq->vring.num. > > > > This causes the device to stop sending used buffer notifications when > > when virtio_packed_should_notify() is called less than once each time > > around the used ring. > > > > It is possible to trigger this with virtio-blk's dataplane > > notify_guest_bh() irq coalescing optimization. The call to > > virtio_notify_irqfd() (and virtio_packed_should_notify()) is deferred to > > a BH. If the guest driver is polling it can complete and submit more > > requests before the BH executes, causing the used ring to wrap more than > > once. The result is that the virtio-blk device ceases to raise > > interrupts and I/O hangs. > > > > Cc: Tiwei Bie <tiwei....@intel.com> > > Cc: Jason Wang <jasow...@redhat.com> > > Cc: Michael S. Tsirkin <m...@redhat.com> > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > > Makes sense. Fixes tag?
Good idea.
Fixes: 86044b24e865fb9596ed77a4d0f3af8b90a088a1 ("virtio: basic packed
virtqueue support")
signature.asc
Description: PGP signature
