On Tue, Jul 11, 2023 at 3:25 PM Eugenio Perez Martin <[email protected]> wrote:
> On Tue, Jul 11, 2023 at 9:05 AM Jason Wang <[email protected]> wrote: > > > > On Tue, Jul 11, 2023 at 12:09 PM Zhu, Lingshan <[email protected]> > wrote: > > > > > > > > > > > > On 7/11/2023 10:50 AM, Jason Wang wrote: > > > > On Mon, Jul 10, 2023 at 4:53 PM Zhu Lingshan <[email protected]> > wrote: > > > >> In the poweroff routine, no need to fetch last available index. > > > >> > > > > This is because there's no concept of shutdown in the vhost layer, it > > > > only knows start and stop. > > > > > > > >> This commit also provides a better debug message in the vhost > > > >> caller vhost_virtqueue_stop, > > > > A separate patch is better. > > > OK > > > > > > > >> because if vhost does not fetch > > > >> the last avail idx successfully, maybe the device does not > > > >> suspend, vhost will sync last avail idx to vring used idx as a > > > >> work around, not a failure. > > > > This only happens if we return a negative value? > > > Yes > > > > > > > >> Signed-off-by: Zhu Lingshan <[email protected]> > > > >> --- > > > >> hw/virtio/vhost-vdpa.c | 10 ++++++++++ > > > >> hw/virtio/vhost.c | 2 +- > > > >> 2 files changed, 11 insertions(+), 1 deletion(-) > > > >> > > > >> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c > > > >> index 3c575a9a6e..10b445f64e 100644 > > > >> --- a/hw/virtio/vhost-vdpa.c > > > >> +++ b/hw/virtio/vhost-vdpa.c > > > >> @@ -26,6 +26,7 @@ > > > >> #include "cpu.h" > > > >> #include "trace.h" > > > >> #include "qapi/error.h" > > > >> +#include "sysemu/runstate.h" > > > >> > > > >> /* > > > >> * Return one past the end of the end of section. Be careful with > uint64_t > > > >> @@ -1391,6 +1392,15 @@ static int vhost_vdpa_get_vring_base(struct > vhost_dev *dev, > > > >> struct vhost_vdpa *v = dev->opaque; > > > >> int ret; > > > >> > > > >> + if (runstate_check(RUN_STATE_SHUTDOWN)) { > > > >> + /* > > > >> + * Some devices do not support this call properly, > > > >> + * and we don't need to retrieve the indexes > > > >> + * if it is shutting down > > > >> + */ > > > >> + return 0; > > > > Checking runstate in the vhost code seems like a layer violation. > > > > > > > > What happens without this patch? > > > vhost tries to fetch vring base, > > > vhost_vdpa needs suspend the device before retrieving last_avail_idx. > > > However not all devices can support .suspend properly so this call > > > may fail. > > > > I think this is where I'm lost. If the device doesn't support > > suspending, any reason we only try to fix the case of shutdown? > > > > Btw, the fail is intended: > > > > if (!v->suspended) { > > /* > > * Cannot trust in value returned by device, let vhost recover > used > > * idx from guest. > > */ > > return -1; > > } > > > > The fail is intended, but to recover the last used idx, either from > device or from the guest, is only useful in the case of migration. > Note that we had userspace devices like VDUSE now, so it could be useful in the case of a VDUSE daemon crash or reconnect. > I think the main problem is the error message, actually. But I think > it has no use either to recover last_avail_idx or print a debug > message if we're not migrating. Another solution would be to recover > it from the guest at vhost_vdpa_get_vring_base, but I don't like the > duplication. > > > And if we return to success here, will we go to set an uninitialized > > last avail idx? > > > > It will be either the default value (is set to 0 at > __virtio_queue_reset) or the one received from a migration (at > virtio_load). > 0 is even sub-optimal than the index used. Anyhow, VHOST_DEBUG should not be enabled for production environments. Thanks > > Thanks! > > > r = dev->vhost_ops->vhost_get_vring_base(dev, &state); > > if (r < 0) { > > ... > > }.else { > > virtio_queue_set_last_avail_idx(vdev, idx, state.num); > > } > > > > Thanks > > > > > Then vhost will print an error shows something failed. > > > > > > The error msg is confused, as stated in the commit log, restoring > > > last_avail_idx with guest used idx > > > is a workaround rather than a failure. And no needs to fetch > last_avail_idx > > > when power off. > > > > > > Thanks > > > > > > > > Thanks > > > > > > > >> + } > > > >> + > > > >> if (v->shadow_vqs_enabled) { > > > >> ring->num = virtio_queue_get_last_avail_idx(dev->vdev, > ring->index); > > > >> return 0; > > > >> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > > > >> index 82394331bf..7dd90cff3a 100644 > > > >> --- a/hw/virtio/vhost.c > > > >> +++ b/hw/virtio/vhost.c > > > >> @@ -1262,7 +1262,7 @@ void vhost_virtqueue_stop(struct vhost_dev > *dev, > > > >> > > > >> r = dev->vhost_ops->vhost_get_vring_base(dev, &state); > > > >> if (r < 0) { > > > >> - VHOST_OPS_DEBUG(r, "vhost VQ %u ring restore failed: %d", > idx, r); > > > >> + VHOST_OPS_DEBUG(r, "sync last avail idx to the guest used > idx for vhost VQ %u", idx); > > > >> /* Connection to the backend is broken, so let's sync > internal > > > >> * last avail idx to the device used idx. > > > >> */ > > > >> -- > > > >> 2.39.3 > > > >> > > > > > > >
