Virtualization - Jun 2023 - [PATCH] vhost-vdpa: filter VIRTIO_F_RING_PACKED feature

On Mon, Jun 05, 2023 at 09:54:57AM -0400, Michael S. Tsirkin
wrote:
>On Mon, Jun 05, 2023 at 03:30:35PM +0200, Stefano Garzarella wrote:
>> On Mon, Jun 05, 2023 at 09:00:25AM -0400, Michael S. Tsirkin wrote:
>> > On Mon, Jun 05, 2023 at 02:54:20PM +0200, Stefano Garzarella
wrote:
>> > > On Mon, Jun 05, 2023 at 08:41:54AM -0400, Michael S. Tsirkin
wrote:
>> > > > On Mon, Jun 05, 2023 at 01:06:44PM +0200, Stefano
Garzarella wrote:
>> > > > > vhost-vdpa IOCTLs (eg. VHOST_GET_VRING_BASE,
VHOST_SET_VRING_BASE)
>> > > > > don't support packed virtqueue well yet, so
let's filter the
>> > > > > VIRTIO_F_RING_PACKED feature for now in
vhost_vdpa_get_features().
>> > > > >
>> > > > > This way, even if the device supports it, we
don't risk it being
>> > > > > negotiated, then the VMM is unable to set the vring
state properly.
>> > > > >
>> > > > > Fixes: 4c8cf31885f6 ("vhost: introduce
vDPA-based backend")
>> > > > > Cc: stable at vger.kernel.org
>> > > > > Signed-off-by: Stefano Garzarella <sgarzare at
redhat.com>
>> > > > > ---
>> > > > >
>> > > > > Notes:
>> > > > >     This patch should be applied before the
"[PATCH v2 0/3] vhost_vdpa:
>> > > > >     better PACKED support" series [1] and
backported in stable branches.
>> > > > >
>> > > > >     We can revert it when we are sure that
everything is working with
>> > > > >     packed virtqueues.
>> > > > >
>> > > > >     Thanks,
>> > > > >     Stefano
>> > > > >
>> > > > >     [1]
https://lore.kernel.org/virtualization/20230424225031.18947-1-shannon.nelson at
amd.com/
>> > > >
>> > > > I'm a bit lost here. So why am I merging
"better PACKED support" then?
>> > >
>> > > To really support packed virtqueue with vhost-vdpa, at that
point we would
>> > > also have to revert this patch.
>> > >
>> > > I wasn't sure if you wanted to queue the series for this
merge window.
>> > > In that case do you think it is better to send this patch
only for stable
>> > > branches?
>> > > > Does this patch make them a NOP?
>> > >
>> > > Yep, after applying the "better PACKED support"
series and being
>> > > sure that
>> > > the IOCTLs of vhost-vdpa support packed virtqueue, we should
revert this
>> > > patch.
>> > >
>> > > Let me know if you prefer a different approach.
>> > >
>> > > I'm concerned that QEMU uses vhost-vdpa IOCTLs thinking
that the kernel
>> > > interprets them the right way, when it does not.
>> > >
>> > > Thanks,
>> > > Stefano
>> > >
>> >
>> > If this fixes a bug can you add Fixes tags to each of them? Then
it's ok
>> > to merge in this window. Probably easier than the elaborate
>> > mask/unmask dance.
>>
>> CCing Shannon (the original author of the "better PACKED
support"
>> series).
>>
>> IIUC Shannon is going to send a v3 of that series to fix the
>> documentation, so Shannon can you also add the Fixes tags?
>>
>> Thanks,
>> Stefano
>
>Well this is in my tree already. Just reply with
>Fixes: <>
>to each and I will add these tags.
I tried, but it is not easy since we added the support for packed 
virtqueue in vdpa and vhost incrementally.

Initially I was thinking of adding the same tag used here:

Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")

Then I discovered that vq_state wasn't there, so I was thinking of

Fixes: 530a5678bc00 ("vdpa: support packed virtqueue for
set/get_vq_state()")

So we would have to backport quite a few patches into the stable branches.
I don't know if it's worth it...

I still think it is better to disable packed in the stable branches,
otherwise I have to make a list of all the patches we need.

Any other ideas?

Thanks,
Stefano

On Mon, Jun 05, 2023 at 04:56:37PM +0200, Stefano Garzarella
wrote:
> On Mon, Jun 05, 2023 at 09:54:57AM -0400, Michael S. Tsirkin wrote:
> > On Mon, Jun 05, 2023 at 03:30:35PM +0200, Stefano Garzarella wrote:
> > > On Mon, Jun 05, 2023 at 09:00:25AM -0400, Michael S. Tsirkin
wrote:
> > > > On Mon, Jun 05, 2023 at 02:54:20PM +0200, Stefano Garzarella
wrote:
> > > > > On Mon, Jun 05, 2023 at 08:41:54AM -0400, Michael S.
Tsirkin wrote:
> > > > > > On Mon, Jun 05, 2023 at 01:06:44PM +0200, Stefano
Garzarella wrote:
> > > > > > > vhost-vdpa IOCTLs (eg. VHOST_GET_VRING_BASE,
VHOST_SET_VRING_BASE)
> > > > > > > don't support packed virtqueue well yet,
so let's filter the
> > > > > > > VIRTIO_F_RING_PACKED feature for now in
vhost_vdpa_get_features().
> > > > > > >
> > > > > > > This way, even if the device supports it, we
don't risk it being
> > > > > > > negotiated, then the VMM is unable to set the
vring state properly.
> > > > > > >
> > > > > > > Fixes: 4c8cf31885f6 ("vhost: introduce
vDPA-based backend")
> > > > > > > Cc: stable at vger.kernel.org
> > > > > > > Signed-off-by: Stefano Garzarella
<sgarzare at redhat.com>
> > > > > > > ---
> > > > > > >
> > > > > > > Notes:
> > > > > > >     This patch should be applied before the
"[PATCH v2 0/3] vhost_vdpa:
> > > > > > >     better PACKED support" series [1]
and backported in stable branches.
> > > > > > >
> > > > > > >     We can revert it when we are sure that
everything is working with
> > > > > > >     packed virtqueues.
> > > > > > >
> > > > > > >     Thanks,
> > > > > > >     Stefano
> > > > > > >
> > > > > > >     [1]
https://lore.kernel.org/virtualization/20230424225031.18947-1-shannon.nelson at
amd.com/
> > > > > >
> > > > > > I'm a bit lost here. So why am I merging
"better PACKED support" then?
> > > > >
> > > > > To really support packed virtqueue with vhost-vdpa, at
that point we would
> > > > > also have to revert this patch.
> > > > >
> > > > > I wasn't sure if you wanted to queue the series for
this merge window.
> > > > > In that case do you think it is better to send this
patch only for stable
> > > > > branches?
> > > > > > Does this patch make them a NOP?
> > > > >
> > > > > Yep, after applying the "better PACKED
support" series and being
> > > > > sure that
> > > > > the IOCTLs of vhost-vdpa support packed virtqueue, we
should revert this
> > > > > patch.
> > > > >
> > > > > Let me know if you prefer a different approach.
> > > > >
> > > > > I'm concerned that QEMU uses vhost-vdpa IOCTLs
thinking that the kernel
> > > > > interprets them the right way, when it does not.
> > > > >
> > > > > Thanks,
> > > > > Stefano
> > > > >
> > > >
> > > > If this fixes a bug can you add Fixes tags to each of them?
Then it's ok
> > > > to merge in this window. Probably easier than the elaborate
> > > > mask/unmask dance.
> > > 
> > > CCing Shannon (the original author of the "better PACKED
support"
> > > series).
> > > 
> > > IIUC Shannon is going to send a v3 of that series to fix the
> > > documentation, so Shannon can you also add the Fixes tags?
> > > 
> > > Thanks,
> > > Stefano
> > 
> > Well this is in my tree already. Just reply with
> > Fixes: <>
> > to each and I will add these tags.
> 
> I tried, but it is not easy since we added the support for packed virtqueue
> in vdpa and vhost incrementally.
> 
> Initially I was thinking of adding the same tag used here:
> 
> Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
> 
> Then I discovered that vq_state wasn't there, so I was thinking of
> 
> Fixes: 530a5678bc00 ("vdpa: support packed virtqueue for
set/get_vq_state()")
> 
> So we would have to backport quite a few patches into the stable branches.
> I don't know if it's worth it...
> 
> I still think it is better to disable packed in the stable branches,
> otherwise I have to make a list of all the patches we need.
> 
> Any other ideas?
> 
> Thanks,
> Stefano
OK so. You want me to apply this one now, and fixes in the next
kernel?

-- 
MST

On Mon, Jun 5, 2023 at 10:58?PM Stefano Garzarella <sgarzare at
redhat.com> wrote:
>
> On Mon, Jun 05, 2023 at 09:54:57AM -0400, Michael S. Tsirkin wrote:
> >On Mon, Jun 05, 2023 at 03:30:35PM +0200, Stefano Garzarella wrote:
> >> On Mon, Jun 05, 2023 at 09:00:25AM -0400, Michael S. Tsirkin
wrote:
> >> > On Mon, Jun 05, 2023 at 02:54:20PM +0200, Stefano Garzarella
wrote:
> >> > > On Mon, Jun 05, 2023 at 08:41:54AM -0400, Michael S.
Tsirkin wrote:
> >> > > > On Mon, Jun 05, 2023 at 01:06:44PM +0200, Stefano
Garzarella wrote:
> >> > > > > vhost-vdpa IOCTLs (eg. VHOST_GET_VRING_BASE,
VHOST_SET_VRING_BASE)
> >> > > > > don't support packed virtqueue well yet,
so let's filter the
> >> > > > > VIRTIO_F_RING_PACKED feature for now in
vhost_vdpa_get_features().
> >> > > > >
> >> > > > > This way, even if the device supports it, we
don't risk it being
> >> > > > > negotiated, then the VMM is unable to set the
vring state properly.
> >> > > > >
> >> > > > > Fixes: 4c8cf31885f6 ("vhost: introduce
vDPA-based backend")
> >> > > > > Cc: stable at vger.kernel.org
> >> > > > > Signed-off-by: Stefano Garzarella <sgarzare
at redhat.com>
> >> > > > > ---
> >> > > > >
> >> > > > > Notes:
> >> > > > >     This patch should be applied before the
"[PATCH v2 0/3] vhost_vdpa:
> >> > > > >     better PACKED support" series [1] and
backported in stable branches.
> >> > > > >
> >> > > > >     We can revert it when we are sure that
everything is working with
> >> > > > >     packed virtqueues.
> >> > > > >
> >> > > > >     Thanks,
> >> > > > >     Stefano
> >> > > > >
> >> > > > >     [1]
https://lore.kernel.org/virtualization/20230424225031.18947-1-shannon.nelson at
amd.com/
> >> > > >
> >> > > > I'm a bit lost here. So why am I merging
"better PACKED support" then?
> >> > >
> >> > > To really support packed virtqueue with vhost-vdpa, at
that point we would
> >> > > also have to revert this patch.
> >> > >
> >> > > I wasn't sure if you wanted to queue the series for
this merge window.
> >> > > In that case do you think it is better to send this
patch only for stable
> >> > > branches?
> >> > > > Does this patch make them a NOP?
> >> > >
> >> > > Yep, after applying the "better PACKED
support" series and being
> >> > > sure that
> >> > > the IOCTLs of vhost-vdpa support packed virtqueue, we
should revert this
> >> > > patch.
> >> > >
> >> > > Let me know if you prefer a different approach.
> >> > >
> >> > > I'm concerned that QEMU uses vhost-vdpa IOCTLs
thinking that the kernel
> >> > > interprets them the right way, when it does not.
> >> > >
> >> > > Thanks,
> >> > > Stefano
> >> > >
> >> >
> >> > If this fixes a bug can you add Fixes tags to each of them?
Then it's ok
> >> > to merge in this window. Probably easier than the elaborate
> >> > mask/unmask dance.
> >>
> >> CCing Shannon (the original author of the "better PACKED
support"
> >> series).
> >>
> >> IIUC Shannon is going to send a v3 of that series to fix the
> >> documentation, so Shannon can you also add the Fixes tags?
> >>
> >> Thanks,
> >> Stefano
> >
> >Well this is in my tree already. Just reply with
> >Fixes: <>
> >to each and I will add these tags.
>
> I tried, but it is not easy since we added the support for packed
> virtqueue in vdpa and vhost incrementally.
>
> Initially I was thinking of adding the same tag used here:
>
> Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
>
> Then I discovered that vq_state wasn't there, so I was thinking of
>
> Fixes: 530a5678bc00 ("vdpa: support packed virtqueue for
set/get_vq_state()")
>
> So we would have to backport quite a few patches into the stable branches.
> I don't know if it's worth it...
>
> I still think it is better to disable packed in the stable branches,
> otherwise I have to make a list of all the patches we need.
>
> Any other ideas?
AFAIK, except for vp_vdpa, pds seems to be the first parent that
supports packed virtqueue. Users should not notice anything wrong if
they don't use packed virtqueue. And the problem of vp_vdpa + packed
virtqueue came since the day0 of vp_vdpa. It seems fine to do nothing
I guess.

Thanks
>
> Thanks,
> Stefano
>
>