Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify
On Tue, Oct 05 2021, "Michael S. Tsirkin" wrote:
> On Tue, Oct 05, 2021 at 01:17:51PM +0200, Halil Pasic wrote:
>> On Mon, 4 Oct 2021 16:01:12 -0400
>> "Michael S. Tsirkin" wrote:
>>
>> > >
>> > > Ok, so what about something like
>> > >
>> > > "If FEATURES_OK is not set, the driver MAY change the set of features it
>> > > accepts."
>> > >
>> > > in the device initialization section?
>> >
>> > Maybe "as long as". However Halil implied that some features are not
>> > turned off properly if that happens. Halil could you pls provide
>> > some examples?
>>
>>
>>
>> static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features)
>> {
>> ...
>> if (virtio_has_feature(features, VIRTIO_NET_F_STANDBY)) {
>> qapi_event_send_failover_negotiated(n->netclient_name);
>> qatomic_set(&n->failover_primary_hidden, false);
>> failover_add_primary(n, &err);
>> if (err) {
>> warn_report_err(err);
>> }
>> }
>> }
>>
>> This is probably the only one in QEMU. Back then I stopped looking
>> after the first hit.
After some grepping, I agree that this seems to be the only one.
>>
>> Regards,
>> Halil
>
> Hmm ok more failover issues :(
> This stuff really should be moved to set_status.
Yes, F_STANDBY does not exist for legacy, so performing those actions
when FEATURES_OK is set looks like the right thing to do.
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Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify
On Tue, Oct 05, 2021 at 01:17:51PM +0200, Halil Pasic wrote:
> On Mon, 4 Oct 2021 16:01:12 -0400
> "Michael S. Tsirkin" wrote:
>
> > >
> > > Ok, so what about something like
> > >
> > > "If FEATURES_OK is not set, the driver MAY change the set of features it
> > > accepts."
> > >
> > > in the device initialization section?
> >
> > Maybe "as long as". However Halil implied that some features are not
> > turned off properly if that happens. Halil could you pls provide
> > some examples?
>
>
>
> static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features)
> {
> ...
> if (virtio_has_feature(features, VIRTIO_NET_F_STANDBY)) {
> qapi_event_send_failover_negotiated(n->netclient_name);
> qatomic_set(&n->failover_primary_hidden, false);
> failover_add_primary(n, &err);
> if (err) {
> warn_report_err(err);
> }
> }
> }
>
> This is probably the only one in QEMU. Back then I stopped looking
> after the first hit.
>
> Regards,
> Halil
Hmm ok more failover issues :(
This stuff really should be moved to set_status.
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Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify
On Mon, 4 Oct 2021 16:01:12 -0400
"Michael S. Tsirkin" wrote:
> >
> > Ok, so what about something like
> >
> > "If FEATURES_OK is not set, the driver MAY change the set of features it
> > accepts."
> >
> > in the device initialization section?
>
> Maybe "as long as". However Halil implied that some features are not
> turned off properly if that happens. Halil could you pls provide
> some examples?
static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features)
{
...
if (virtio_has_feature(features, VIRTIO_NET_F_STANDBY)) {
qapi_event_send_failover_negotiated(n->netclient_name);
qatomic_set(&n->failover_primary_hidden, false);
failover_add_primary(n, &err);
if (err) {
warn_report_err(err);
}
}
}
This is probably the only one in QEMU. Back then I stopped looking
after the first hit.
Regards,
Halil
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Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify
On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: > On Mon, Oct 04, 2021 at 05:45:06PM +0200, Cornelia Huck wrote: >> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: >> >> > On Mon, Oct 04, 2021 at 04:27:23PM +0200, Cornelia Huck wrote: >> >> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: >> >> >> >> > Do we want to also add explanation that features can be >> >> > changed until FEATURES_OK? >> >> >> >> I always considered that to be implict, as feature negotiation is not >> >> over until we have FEATURES_OK. Not sure whether we need an extra note. >> > >> > Well Halil here says once you set a feature bit you can't clear it. >> > So maybe not ... >> >> Ok, so what about something like >> >> "If FEATURES_OK is not set, the driver MAY change the set of features it >> accepts." >> >> in the device initialization section? > > Maybe "as long as". However Halil implied that some features are not > turned off properly if that happens. Halil could you pls provide > some examples? Yes, "as long as" sounds better. ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify
On Mon, Oct 04, 2021 at 05:45:06PM +0200, Cornelia Huck wrote:
> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote:
>
> > On Mon, Oct 04, 2021 at 04:27:23PM +0200, Cornelia Huck wrote:
> >> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote:
> >>
> >> > On Mon, Oct 04, 2021 at 02:01:14PM +0200, Cornelia Huck wrote:
> >> >> On Sun, Oct 03 2021, "Michael S. Tsirkin" wrote:
> >> >> > @@ -160,6 +163,33 @@ \subsection{Legacy Interface: A Note on Feature
> >> >> > Specification text within these sections generally does not apply
> >> >> > to non-transitional devices.
> >> >> >
> >> >> > +\begin{note}
> >> >> > +The device offers different features when used through
> >> >> > +the legacy interface and when operated in accordance with this
> >> >> > +specification.
> >> >> > +\end{note}
> >> >> > +
> >> >> > +Transitional drivers MUST use Devices only through the legacy
> >> >> > interface
> >> >>
> >> >> s/Devices only through the legacy interface/devices through the legacy
> >> >> interface only/
> >> >>
> >> >> ?
> >> >
> >> > Both versions are actually confused, since how do you
> >> > find out that device does not offer VIRTIO_F_VERSION_1?
> >> >
> >> > I think what this should really say is
> >> >
> >> > Transitional drivers MUST NOT accept VIRTIO_F_VERSION_1 through
> >> > the legacy interface.
> >>
> >> Ok, that makes sense.
> >>
> >> Would it make sense that transitional drivers MUST accept VERSION_1
> >> through the non-legacy interface? Or is that redundant?
> >
> > We already have:
> >
> > A driver MUST accept VIRTIO_F_VERSION_1 if it is offered.
>
> Yep, so it is redundant.
>
> >
> >
> >> >
> >> >
> >> > Does linux actually satisfy this? Will it accept VIRTIO_F_VERSION_1
> >> > through the legacy interface if offered?
> >>
> >> I think that the Linux drivers will not operate on feature bit 32+ if
> >> they are in legacy mode?
> >
> >
> > Well ... with PCI there's no *way* for host to set bit 32 through
> > legacy. But it might be possible with MMIO/CCW. Can you tell me
> > what happens then?
>
> ccw does not support accessing bit 32+, either. Not sure about mmio.
>
> >
> >
> >> >>
> >> >> Generally, looks good to me.
> >> >
> >> > Do we want to also add explanation that features can be
> >> > changed until FEATURES_OK?
> >>
> >> I always considered that to be implict, as feature negotiation is not
> >> over until we have FEATURES_OK. Not sure whether we need an extra note.
> >
> > Well Halil here says once you set a feature bit you can't clear it.
> > So maybe not ...
>
> Ok, so what about something like
>
> "If FEATURES_OK is not set, the driver MAY change the set of features it
> accepts."
>
> in the device initialization section?
Maybe "as long as". However Halil implied that some features are not
turned off properly if that happens. Halil could you pls provide
some examples?
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Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify
On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote:
> On Mon, Oct 04, 2021 at 04:27:23PM +0200, Cornelia Huck wrote:
>> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote:
>>
>> > On Mon, Oct 04, 2021 at 02:01:14PM +0200, Cornelia Huck wrote:
>> >> On Sun, Oct 03 2021, "Michael S. Tsirkin" wrote:
>> >> > @@ -160,6 +163,33 @@ \subsection{Legacy Interface: A Note on Feature
>> >> > Specification text within these sections generally does not apply
>> >> > to non-transitional devices.
>> >> >
>> >> > +\begin{note}
>> >> > +The device offers different features when used through
>> >> > +the legacy interface and when operated in accordance with this
>> >> > +specification.
>> >> > +\end{note}
>> >> > +
>> >> > +Transitional drivers MUST use Devices only through the legacy interface
>> >>
>> >> s/Devices only through the legacy interface/devices through the legacy
>> >> interface only/
>> >>
>> >> ?
>> >
>> > Both versions are actually confused, since how do you
>> > find out that device does not offer VIRTIO_F_VERSION_1?
>> >
>> > I think what this should really say is
>> >
>> > Transitional drivers MUST NOT accept VIRTIO_F_VERSION_1 through
>> > the legacy interface.
>>
>> Ok, that makes sense.
>>
>> Would it make sense that transitional drivers MUST accept VERSION_1
>> through the non-legacy interface? Or is that redundant?
>
> We already have:
>
> A driver MUST accept VIRTIO_F_VERSION_1 if it is offered.
Yep, so it is redundant.
>
>
>> >
>> >
>> > Does linux actually satisfy this? Will it accept VIRTIO_F_VERSION_1
>> > through the legacy interface if offered?
>>
>> I think that the Linux drivers will not operate on feature bit 32+ if
>> they are in legacy mode?
>
>
> Well ... with PCI there's no *way* for host to set bit 32 through
> legacy. But it might be possible with MMIO/CCW. Can you tell me
> what happens then?
ccw does not support accessing bit 32+, either. Not sure about mmio.
>
>
>> >>
>> >> Generally, looks good to me.
>> >
>> > Do we want to also add explanation that features can be
>> > changed until FEATURES_OK?
>>
>> I always considered that to be implict, as feature negotiation is not
>> over until we have FEATURES_OK. Not sure whether we need an extra note.
>
> Well Halil here says once you set a feature bit you can't clear it.
> So maybe not ...
Ok, so what about something like
"If FEATURES_OK is not set, the driver MAY change the set of features it
accepts."
in the device initialization section?
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