Jason Wang
2023-Jul-07 07:57 UTC
[PATCH] vdpa: reject F_ENABLE_AFTER_DRIVER_OK if backend does not support it
On Thu, Jul 6, 2023 at 5:39?PM Eugenio Perez Martin <eperezma at redhat.com> wrote:> > On Thu, Jul 6, 2023 at 10:03?AM Jason Wang <jasowang at redhat.com> wrote: > > > > On Thu, Jul 6, 2023 at 3:55?PM Jason Wang <jasowang at redhat.com> wrote: > > > > > > On Thu, Jul 6, 2023 at 3:06?PM Eugenio Perez Martin <eperezma at redhat.com> wrote: > > > > > > > > On Thu, Jul 6, 2023 at 3:55?AM Jason Wang <jasowang at redhat.com> wrote: > > > > > > > > > > On Wed, Jul 5, 2023 at 4:41?PM Michael S. Tsirkin <mst at redhat.com> wrote: > > > > > > > > > > > > On Wed, Jul 05, 2023 at 03:49:58PM +0800, Jason Wang wrote: > > > > > > > On Tue, Jul 4, 2023 at 11:45?PM Michael S. Tsirkin <mst at redhat.com> wrote: > > > > > > > > > > > > > > > > On Tue, Jul 04, 2023 at 01:36:11PM +0200, Eugenio Perez Martin wrote: > > > > > > > > > On Tue, Jul 4, 2023 at 12:38?PM Michael S. Tsirkin <mst at redhat.com> wrote: > > > > > > > > > > > > > > > > > > > > On Tue, Jul 04, 2023 at 12:25:32PM +0200, Eugenio Perez Martin wrote: > > > > > > > > > > > On Mon, Jul 3, 2023 at 4:52?PM Michael S. Tsirkin <mst at redhat.com> wrote: > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Jul 03, 2023 at 04:22:18PM +0200, Eugenio P?rez wrote: > > > > > > > > > > > > > With the current code it is accepted as long as userland send it. > > > > > > > > > > > > > > > > > > > > > > > > > > Although userland should not set a feature flag that has not been > > > > > > > > > > > > > offered to it with VHOST_GET_BACKEND_FEATURES, the current code will not > > > > > > > > > > > > > complain for it. > > > > > > > > > > > > > > > > > > > > > > > > > > Since there is no specific reason for any parent to reject that backend > > > > > > > > > > > > > feature bit when it has been proposed, let's control it at vdpa frontend > > > > > > > > > > > > > level. Future patches may move this control to the parent driver. > > > > > > > > > > > > > > > > > > > > > > > > > > Fixes: 967800d2d52e ("vdpa: accept VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK backend feature") > > > > > > > > > > > > > Signed-off-by: Eugenio P?rez <eperezma at redhat.com> > > > > > > > > > > > > > > > > > > > > > > > > Please do send v3. And again, I don't want to send "after driver ok" hack > > > > > > > > > > > > upstream at all, I merged it in next just to give it some testing. > > > > > > > > > > > > We want RING_ACCESS_AFTER_KICK or some such. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Current devices do not support that semantic. > > > > > > > > > > > > > > > > > > > > Which devices specifically access the ring after DRIVER_OK but before > > > > > > > > > > a kick? > > > > > > > > > > > > > > > > > > > > > > > > > > > > Previous versions of the QEMU LM series did a spurious kick to start > > > > > > > > > traffic at the LM destination [1]. When it was proposed, that spurious > > > > > > > > > kick was removed from the series because to check for descriptors > > > > > > > > > after driver_ok, even without a kick, was considered work of the > > > > > > > > > parent driver. > > > > > > > > > > > > > > > > > > I'm ok to go back to this spurious kick, but I'm not sure if the hw > > > > > > > > > will read the ring before the kick actually. I can ask. > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > > > > > > > > > > [1] https://lists.nongnu.org/archive/html/qemu-devel/2023-01/msg02775.html > > > > > > > > > > > > > > > > Let's find out. We need to check for ENABLE_AFTER_DRIVER_OK too, no? > > > > > > > > > > > > > > My understanding is [1] assuming ACCESS_AFTER_KICK. This seems > > > > > > > sub-optimal than assuming ENABLE_AFTER_DRIVER_OK. > > > > > > > > > > > > > > But this reminds me one thing, as the thread is going too long, I > > > > > > > wonder if we simply assume ENABLE_AFTER_DRIVER_OK if RING_RESET is > > > > > > > supported? > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > I don't see what does one have to do with another ... > > > > > > > > > > > > I think with RING_RESET we had another solution, enable rings > > > > > > mapping them to a zero page, then reset and re-enable later. > > > > > > > > > > As discussed before, this seems to have some problems: > > > > > > > > > > 1) The behaviour is not clarified in the document > > > > > 2) zero is a valid IOVA > > > > > > > > > > > > > I think we're not on the same page here. > > > > > > > > As I understood, rings mapped to a zero page means essentially an > > > > avail ring whose avail_idx is always 0, offered to the device instead > > > > of the guest's ring. Once all CVQ commands are processed, we use > > > > RING_RESET to switch to the right ring, being guest's or SVQ vring. > > > > > > I get this. This seems more complicated in the destination: shadow vq + ASID? > > > > So it's something like: > > > > 1) set all vq ASID to shadow virtqueue > > 2) do not add any bufs to data qp (stick 0 as avail index) > > 3) start to restore states via cvq > > 4) ring_rest for dataqp > > 5) set_vq_state for dataqp > > 6) re-initialize dataqp address etc > > 7) set data QP ASID to guest > > 8) set queue_enable > > > > ? > > > > I think the change of ASID is not needed, as the guest cannot access > the device in that timeframe anyway.Yes but after the restore, we still want to shadow cvq, so ASID is still needed? Thanks> Moreover, it may require HW > support. So steps 1 and 7 are not needed. > > Apart from that, the process is right. > > > > Thanks > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > My plan was to convert > > > > > > > > > > > it in vp_vdpa if needed, and reuse the current vdpa ops. Sorry if I > > > > > > > > > > > was not explicit enough. > > > > > > > > > > > > > > > > > > > > > > The only solution I can see to that is to trap & emulate in the vdpa > > > > > > > > > > > (parent?) driver, as talked in virtio-comment. But that complicates > > > > > > > > > > > the architecture: > > > > > > > > > > > * Offer VHOST_BACKEND_F_RING_ACCESS_AFTER_KICK > > > > > > > > > > > * Store vq enable state separately, at > > > > > > > > > > > vdpa->config->set_vq_ready(true), but not transmit that enable to hw > > > > > > > > > > > * Store the doorbell state separately, but do not configure it to the > > > > > > > > > > > device directly. > > > > > > > > > > > > > > > > > > > > > > But how to recover if the device cannot configure them at kick time, > > > > > > > > > > > for example? > > > > > > > > > > > > > > > > > > > > > > Maybe we can just fail if the parent driver does not support enabling > > > > > > > > > > > the vq after DRIVER_OK? That way no new feature flag is needed. > > > > > > > > > > > > > > > > > > > > > > Thanks! > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --- > > > > > > > > > > > > > Sent with Fixes: tag pointing to git.kernel.org/pub/scm/linux/kernel/git/mst > > > > > > > > > > > > > commit. Please let me know if I should send a v3 of [1] instead. > > > > > > > > > > > > > > > > > > > > > > > > > > [1] https://lore.kernel.org/lkml/20230609121244-mutt-send-email-mst at kernel.org/T/ > > > > > > > > > > > > > --- > > > > > > > > > > > > > drivers/vhost/vdpa.c | 7 +++++-- > > > > > > > > > > > > > 1 file changed, 5 insertions(+), 2 deletions(-) > > > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c > > > > > > > > > > > > > index e1abf29fed5b..a7e554352351 100644 > > > > > > > > > > > > > --- a/drivers/vhost/vdpa.c > > > > > > > > > > > > > +++ b/drivers/vhost/vdpa.c > > > > > > > > > > > > > @@ -681,18 +681,21 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep, > > > > > > > > > > > > > { > > > > > > > > > > > > > struct vhost_vdpa *v = filep->private_data; > > > > > > > > > > > > > struct vhost_dev *d = &v->vdev; > > > > > > > > > > > > > + const struct vdpa_config_ops *ops = v->vdpa->config; > > > > > > > > > > > > > void __user *argp = (void __user *)arg; > > > > > > > > > > > > > u64 __user *featurep = argp; > > > > > > > > > > > > > - u64 features; > > > > > > > > > > > > > + u64 features, parent_features = 0; > > > > > > > > > > > > > long r = 0; > > > > > > > > > > > > > > > > > > > > > > > > > > if (cmd == VHOST_SET_BACKEND_FEATURES) { > > > > > > > > > > > > > if (copy_from_user(&features, featurep, sizeof(features))) > > > > > > > > > > > > > return -EFAULT; > > > > > > > > > > > > > + if (ops->get_backend_features) > > > > > > > > > > > > > + parent_features = ops->get_backend_features(v->vdpa); > > > > > > > > > > > > > if (features & ~(VHOST_VDPA_BACKEND_FEATURES | > > > > > > > > > > > > > BIT_ULL(VHOST_BACKEND_F_SUSPEND) | > > > > > > > > > > > > > BIT_ULL(VHOST_BACKEND_F_RESUME) | > > > > > > > > > > > > > - BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK))) > > > > > > > > > > > > > + parent_features)) > > > > > > > > > > > > > return -EOPNOTSUPP; > > > > > > > > > > > > > if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) && > > > > > > > > > > > > > !vhost_vdpa_can_suspend(v)) > > > > > > > > > > > > > -- > > > > > > > > > > > > > 2.39.3 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >