Re: [PATCH] virtio_pmem: Add freeze/restore callbacks

[Philip Chen]

Hi

On Wed, Sep 4, 2024 at 10:54 AM Ira Weiny <ira.weiny@xxxxxxxxx> wrote:
>
> Philip Chen wrote:
> > Hi maintainers,
> >
> > Can anyone let me know if this patch makes sense?
> > Any comment/feedback is appreciated.
> > Thanks in advance!
>
> I'm not an expert on virtio but the code looks ok on the surface.  I've
> discussed this with Dan a bit and virtio-pmem is not heavily tested.

Thanks for your comments.
I think this specific patch is not heavily involved with virtio spec details.
This patch simply provides the basic freeze/restore PM callbacks for
virtio_pmem, like people already did for the other virtio drivers.

>
> Based on our discussion [1] I wonder if there is a way we can recreate this
> with QEMU to incorporate into our testing?

Yes, these are how I test on crosvm, but I believe the same steps can
be applied to QEMU:
(1) Set pm_test_level to TEST_PLATFORM (build time change)
(2) Write something to pmem
(3) Make the device go through a freeze/restore cycle by writing
`disk` to `/sys/power/state`
(4) Validate the data written to pmem in (2) is still preserved

Note:
(a) The freeze/restore PM routines are sometimes called as the backup
for suspend/resume PM routines in a suspend/resume cycle.
In this case, we can also test freeze/restore PM routines with
suspend/resume: i.e. skip (1) and write `mem` to `sys/power/state` in
(3).
(b) I also tried to set up QEMU for testing. But QEMU crashes when I
try to freeze the device even without applying this patch.
Since the issue seems to be irrelevant to pmem and most likely a QEMU
setup problem on my end, I didn't spend more time enabling QEMU.



>
> Ira
>
> [1] https://lore.kernel.org/lkml/CA+cxXhnb2i5O7_BiOfKLth5Zwp5T62d6F6c39vnuT53cUkU_uw@xxxxxxxxxxxxxx/
>
> >
> > On Wed, Aug 14, 2024 at 5:46 PM Philip Chen <philipchen@xxxxxxxxxxxx> wrote:
> > >
> > > Add basic freeze/restore PM callbacks to support hibernation (S4):
> > > - On freeze, delete vq and quiesce the device to prepare for
> > >   snapshotting.
> > > - On restore, re-init vq and mark DRIVER_OK.
> > >
> > > Signed-off-by: Philip Chen <philipchen@xxxxxxxxxxxx>
> > > ---
> > >  drivers/nvdimm/virtio_pmem.c | 24 ++++++++++++++++++++++++
> > >  1 file changed, 24 insertions(+)
> > >
> > > diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> > > index c9b97aeabf85..2396d19ce549 100644
> > > --- a/drivers/nvdimm/virtio_pmem.c
> > > +++ b/drivers/nvdimm/virtio_pmem.c
> > > @@ -143,6 +143,28 @@ static void virtio_pmem_remove(struct virtio_device *vdev)
> > >         virtio_reset_device(vdev);
> > >  }
> > >
> > > +static int virtio_pmem_freeze(struct virtio_device *vdev)
> > > +{
> > > +       vdev->config->del_vqs(vdev);
> > > +       virtio_reset_device(vdev);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +static int virtio_pmem_restore(struct virtio_device *vdev)
> > > +{
> > > +       int ret;
> > > +
> > > +       ret = init_vq(vdev->priv);
> > > +       if (ret) {
> > > +               dev_err(&vdev->dev, "failed to initialize virtio pmem's vq\n");
> > > +               return ret;
> > > +       }
> > > +       virtio_device_ready(vdev);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > >  static unsigned int features[] = {
> > >         VIRTIO_PMEM_F_SHMEM_REGION,
> > >  };
> > > @@ -155,6 +177,8 @@ static struct virtio_driver virtio_pmem_driver = {
> > >         .validate               = virtio_pmem_validate,
> > >         .probe                  = virtio_pmem_probe,
> > >         .remove                 = virtio_pmem_remove,
> > > +       .freeze                 = virtio_pmem_freeze,
> > > +       .restore                = virtio_pmem_restore,
> > >  };
> > >
> > >  module_virtio_driver(virtio_pmem_driver);
> > > --
> > > 2.46.0.76.ge559c4bf1a-goog
> > >
>
>