Messages in this thread | | | From | Eugenio Perez Martin <> | Date | Thu, 19 Jan 2023 09:10:45 +0100 | Subject | Re: [PATCH 2/2] vringh: fetch used_idx from vring at vringh_init_iotlb |
| |
On Thu, Jan 19, 2023 at 4:20 AM Jason Wang <jasowang@redhat.com> wrote: > > On Thu, Jan 19, 2023 at 12:44 AM Eugenio Pérez <eperezma@redhat.com> wrote: > > > > Starting from an used_idx different than 0 is needed in use cases like > > virtual machine migration. Not doing so and letting the caller set an > > avail idx different than 0 causes destination device to try to use old > > buffers that source driver already recover and are not available > > anymore. > > > > While callers like vdpa_sim set avail_idx directly it does not set > > used_idx. Instead of let the caller do the assignment, fetch it from > > the guest at initialization like vhost-kernel do. > > > > To perform the same at vring_kernel_init and vring_user_init is left for > > the future. > > > > Signed-off-by: Eugenio Pérez <eperezma@redhat.com> > > --- > > drivers/vhost/vringh.c | 25 +++++++++++++++++++++++-- > > 1 file changed, 23 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c > > index 33eb941fcf15..0eed825197f2 100644 > > --- a/drivers/vhost/vringh.c > > +++ b/drivers/vhost/vringh.c > > @@ -1301,6 +1301,17 @@ static inline int putused_iotlb(const struct vringh *vrh, > > return 0; > > } > > > > +/** > > + * vringh_update_used_idx - fetch used idx from driver's used split vring > > + * @vrh: The vring. > > + * > > + * Returns -errno or 0. > > + */ > > +static inline int vringh_update_used_idx(struct vringh *vrh) > > +{ > > + return getu16_iotlb(vrh, &vrh->last_used_idx, &vrh->vring.used->idx); > > +} > > + > > /** > > * vringh_init_iotlb - initialize a vringh for a ring with IOTLB. > > * @vrh: the vringh to initialize. > > @@ -1319,8 +1330,18 @@ int vringh_init_iotlb(struct vringh *vrh, u64 features, > > struct vring_avail *avail, > > struct vring_used *used) > > { > > While at this, I wonder if it's better to have a dedicated parameter > for last_avail_idx? >
I also had that thought. To directly assign last_avail_idx is not a specially elegant API IMO.
Maybe expose a way to fetch used_idx from device vring and pass used_idx as parameter too?
> > - return vringh_init_kern(vrh, features, num, weak_barriers, > > - desc, avail, used); > > + int r = vringh_init_kern(vrh, features, num, weak_barriers, desc, > > + avail, used); > > + > > + if (r != 0) > > + return r; > > + > > + /* Consider the ring not initialized */ > > + if ((void *)desc == used) > > + return 0; > > I don't understand when we can get this (actually it should be a bug > of the caller). >
You can see it in vdpasim_vq_reset.
Note that to consider desc == 0 to be an uninitialized ring is a bug IMO. QEMU considers it that way also, but the standard does not forbid any ring to be at address 0. Especially if we use vIOMMU.
So I think the best way to know if we can use the vringh is either this way, or provide an explicit "initialized" boolean attribute. Maybe a new "bool is_initialized(vrh)" is enough, if we don't want to add new attributes.
Thanks!
> Thanks > > > + > > + return vringh_update_used_idx(vrh); > > + > > } > > EXPORT_SYMBOL(vringh_init_iotlb); > > > > -- > > 2.31.1 > > >
| |