Re: [PATCH] virtio: skip guest index check on device load

[Stefan Hajnoczi]

On Wed, Oct 28, 2020 at 07:30:55AM -0400, Michael S. Tsirkin wrote:
> On Wed, Oct 28, 2020 at 11:00:38AM +0000, Stefan Hajnoczi wrote:
> > On Tue, Oct 27, 2020 at 09:04:46AM -0400, Michael S. Tsirkin wrote:
> > > It's not a waste of time, it's just a lot of work
> > > within guests.
> > 
> > Luckily it does no harm to set the NEEDS_RESET bit even if the guest
> > doesn't handle it.
> > 
> > If the guest driver is unaware it may continue to submit requests to the
> > device for a while. The device emulation code stops accepting new
> > requests though. This means the device will become unresponsive until
> > reset, which is not ideal but okay in the case where the device was put
> > into an invalid state.
> 
> There is no actual rule that device must stop processing requests.
> Driver can only assume that is the case after it started the
> actual reset.

Right, I mean QEMU's implementation stops processing new requests once
the device has been marked "broken":

  void *virtqueue_pop(VirtQueue *vq, size_t sz)
  {
      if (virtio_device_disabled(vq->vdev)) { <---
          return NULL;

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