Jason Wang
2023-Jan-29 06:00 UTC
[PATCH 2/2] vringh: fetch used_idx from vring at vringh_init_iotlb
On Thu, Jan 19, 2023 at 4:11 PM Eugenio Perez Martin <eperezma at redhat.com> wrote:> > On Thu, Jan 19, 2023 at 4:20 AM Jason Wang <jasowang at redhat.com> wrote: > > > > On Thu, Jan 19, 2023 at 12:44 AM Eugenio P?rez <eperezma at 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 P?rez <eperezma at 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?If I was not wrong, we can start from last_avail_idx, for used_idx it is only needed for inflight descriptors which might require other APIs? (All the current vDPA user of vringh is doing in order processing)> > > > - 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.I wonder if we can avoid this in the simulator level instead of the vringh (anyhow it only exposes a vringh_init_xxx() helper now). Thanks> > Thanks! > > > Thanks > > > > > + > > > + return vringh_update_used_idx(vrh); > > > + > > > } > > > EXPORT_SYMBOL(vringh_init_iotlb); > > > > > > -- > > > 2.31.1 > > > > > >