Re: [PATCH 28/31] vdpa: Expose VHOST_F_LOG_ALL on SVQ

[Jason Wang]

在 2022/2/1 下午7:45, Eugenio Perez Martin 写道:
> On Sun, Jan 30, 2022 at 7:50 AM Jason Wang <jasowang@redhat.com> wrote:
> > 在 2022/1/22 上午4:27, Eugenio Pérez 写道:
> > > SVQ is able to log the dirty bits by itself, so let's use it to not
> > > block migration.
> > >
> > > Also, ignore set and clear of VHOST_F_LOG_ALL on set_features if SVQ is
> > > enabled. Even if the device supports it, the reports would be nonsense
> > > because SVQ memory is in the qemu region.
> > >
> > > The log region is still allocated. Future changes might skip that, but
> > > this series is already long enough.
> > >
> > > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > > ---
> > >    hw/virtio/vhost-vdpa.c | 20 ++++++++++++++++++++
> > >    1 file changed, 20 insertions(+)
> > >
> > > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > > index fb0a338baa..75090d65e8 100644
> > > --- a/hw/virtio/vhost-vdpa.c
> > > +++ b/hw/virtio/vhost-vdpa.c
> > > @@ -1022,6 +1022,9 @@ static int vhost_vdpa_get_features(struct vhost_dev *dev, 
> > > uint64_t *features)
> > >        if (ret == 0 && v->shadow_vqs_enabled) {
> > >            /* Filter only features that SVQ can offer to guest */
> > >            vhost_svq_valid_guest_features(features);
> > > +
> > > +        /* Add SVQ logging capabilities */
> > > +        *features |= BIT_ULL(VHOST_F_LOG_ALL);
> > >        }
> > >
> > >        return ret;
> > > @@ -1039,8 +1042,25 @@ static int vhost_vdpa_set_features(struct vhost_dev *dev,
> > >
> > >        if (v->shadow_vqs_enabled) {
> > >            uint64_t dev_features, svq_features, acked_features;
> > > +        uint8_t status = 0;
> > >            bool ok;
> > >
> > > +        ret = vhost_vdpa_call(dev, VHOST_VDPA_GET_STATUS, &status);
> > > +        if (unlikely(ret)) {
> > > +            return ret;
> > > +        }
> > > +
> > > +        if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
> > > +            /*
> > > +             * vhost is trying to enable or disable _F_LOG, and the device
> > > +             * would report wrong dirty pages. SVQ handles it.
> > > +             */
> >
> > I fail to understand this comment, I'd think there's no way to disable
> > dirty page tracking for SVQ.
> vhost_log_global_{start,stop} are called at the beginning and end of
> migration. To inform the device that it should start logging, they set
> or clean VHOST_F_LOG_ALL at vhost_dev_set_log.


Yes, but for SVQ, we can't disable dirty page tracking, isn't it? The 
only thing is to ignore or filter out the F_LOG_ALL and pretend to be 
enabled and disabled.


> While SVQ does not use VHOST_F_LOG_ALL, it exports the feature bit so
> vhost does not block migration. Maybe we need to look for another way
> to do this?


I'm fine with filtering since it's much more simpler, but I fail to 
understand why we need to check DRIVER_OK.

Thanks


> Thanks!
>
> > Thanks
> >
> >
> > > +            return 0;
> > > +        }
> > > +
> > > +        /* We must not ack _F_LOG if SVQ is enabled */
> > > +        features &= ~BIT_ULL(VHOST_F_LOG_ALL);
> > > +
> > >            ret = vhost_vdpa_get_dev_features(dev, &dev_features);
> > >            if (ret != 0) {
> > >                error_report("Can't get vdpa device features, got (%d)", ret);