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Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff
From: |
Jason Wang |
Subject: |
Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff |
Date: |
Tue, 11 Jul 2023 15:05:17 +0800 |
On Tue, Jul 11, 2023 at 12:09 PM Zhu, Lingshan <lingshan.zhu@intel.com> wrote:
>
>
>
> On 7/11/2023 10:50 AM, Jason Wang wrote:
> > On Mon, Jul 10, 2023 at 4:53 PM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
> >> In the poweroff routine, no need to fetch last available index.
> >>
> > This is because there's no concept of shutdown in the vhost layer, it
> > only knows start and stop.
> >
> >> This commit also provides a better debug message in the vhost
> >> caller vhost_virtqueue_stop,
> > A separate patch is better.
> OK
> >
> >> because if vhost does not fetch
> >> the last avail idx successfully, maybe the device does not
> >> suspend, vhost will sync last avail idx to vring used idx as a
> >> work around, not a failure.
> > This only happens if we return a negative value?
> Yes
> >
> >> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> >> ---
> >> hw/virtio/vhost-vdpa.c | 10 ++++++++++
> >> hw/virtio/vhost.c | 2 +-
> >> 2 files changed, 11 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> >> index 3c575a9a6e..10b445f64e 100644
> >> --- a/hw/virtio/vhost-vdpa.c
> >> +++ b/hw/virtio/vhost-vdpa.c
> >> @@ -26,6 +26,7 @@
> >> #include "cpu.h"
> >> #include "trace.h"
> >> #include "qapi/error.h"
> >> +#include "sysemu/runstate.h"
> >>
> >> /*
> >> * Return one past the end of the end of section. Be careful with
> >> uint64_t
> >> @@ -1391,6 +1392,15 @@ static int vhost_vdpa_get_vring_base(struct
> >> vhost_dev *dev,
> >> struct vhost_vdpa *v = dev->opaque;
> >> int ret;
> >>
> >> + if (runstate_check(RUN_STATE_SHUTDOWN)) {
> >> + /*
> >> + * Some devices do not support this call properly,
> >> + * and we don't need to retrieve the indexes
> >> + * if it is shutting down
> >> + */
> >> + return 0;
> > Checking runstate in the vhost code seems like a layer violation.
> >
> > What happens without this patch?
> vhost tries to fetch vring base,
> vhost_vdpa needs suspend the device before retrieving last_avail_idx.
> However not all devices can support .suspend properly so this call
> may fail.
I think this is where I'm lost. If the device doesn't support
suspending, any reason we only try to fix the case of shutdown?
Btw, the fail is intended:
if (!v->suspended) {
/*
* Cannot trust in value returned by device, let vhost recover used
* idx from guest.
*/
return -1;
}
And if we return to success here, will we go to set an uninitialized
last avail idx?
r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
if (r < 0) {
...
}.else {
virtio_queue_set_last_avail_idx(vdev, idx, state.num);
}
Thanks
> Then vhost will print an error shows something failed.
>
> The error msg is confused, as stated in the commit log, restoring
> last_avail_idx with guest used idx
> is a workaround rather than a failure. And no needs to fetch last_avail_idx
> when power off.
>
> Thanks
> >
> > Thanks
> >
> >> + }
> >> +
> >> if (v->shadow_vqs_enabled) {
> >> ring->num = virtio_queue_get_last_avail_idx(dev->vdev,
> >> ring->index);
> >> return 0;
> >> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> >> index 82394331bf..7dd90cff3a 100644
> >> --- a/hw/virtio/vhost.c
> >> +++ b/hw/virtio/vhost.c
> >> @@ -1262,7 +1262,7 @@ void vhost_virtqueue_stop(struct vhost_dev *dev,
> >>
> >> r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
> >> if (r < 0) {
> >> - VHOST_OPS_DEBUG(r, "vhost VQ %u ring restore failed: %d", idx, r);
> >> + VHOST_OPS_DEBUG(r, "sync last avail idx to the guest used idx for
> >> vhost VQ %u", idx);
> >> /* Connection to the backend is broken, so let's sync internal
> >> * last avail idx to the device used idx.
> >> */
> >> --
> >> 2.39.3
> >>
>
- [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Zhu Lingshan, 2023/07/10
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Eugenio Perez Martin, 2023/07/10
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Jason Wang, 2023/07/10
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Zhu, Lingshan, 2023/07/11
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff,
Jason Wang <=
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Eugenio Perez Martin, 2023/07/11
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Jason Wang, 2023/07/11
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Zhu, Lingshan, 2023/07/12
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Jason Wang, 2023/07/12
- Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff, Zhu, Lingshan, 2023/07/12