linux-kernel - Re: [PATCH] virtio_pmem: Add freeze/restore callbacks

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Message-ID: <CAM9Jb+gj2e0A-3=gmvUUWWEzjpEHfJhaqnSKPmhg4E4ucXgexg@mail.gmail.com>
Date: Wed, 25 Sep 2024 09:30:29 +0200
From: Pankaj Gupta <pankaj.gupta.linux@...il.com>
To: Philip Chen <philipchen@...omium.org>
Cc: Ira Weiny <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>, 
	Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, 
	virtualization@...ts.linux.dev, nvdimm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, "Michael S . Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH] virtio_pmem: Add freeze/restore callbacks

+CC MST

> > 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.

Thanks for the work!

Did you check why QEMU was crashing, maybe because we did not support
freeze/restore before
so some missing NULL check? Any back trace you got?

If it works in crossVM, it should work in Qemu as well?

Thanks,
Pankaj

>
>
>
> >
> > Ira
> >
> > [1] https://lore.kernel.org/lkml/CA+cxXhnb2i5O7_BiOfKLth5Zwp5T62d6F6c39vnuT53cUkU_uw@mail.gmail.com/
> >
> > >
> > > On Wed, Aug 14, 2024 at 5:46 PM Philip Chen <philipchen@...omium.org> 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@...omium.org>
> > > > ---
> > > >  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
> > > >
> >
> >