On Tue, Jul 11, 2023 at 9:05 AM Jason Wang <jasow...@redhat.com> wrote: > > On Tue, Jul 11, 2023 at 12:09 PM Zhu, Lingshan <lingshan....@intel.com> wrote: > > > > > > > > On 7/11/2023 10:50 AM, Jason Wang wrote: > > > On Mon, Jul 10, 2023 at 4:53 PM Zhu Lingshan <lingshan....@intel.com> > > > 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 <lingshan....@intel.com> > > >> --- > > >> 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. 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). 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 > > >> > > >