Re: [PATCH] vp_vdpa: harden the logic of set status

[Longpeng (Mike, Cloud Infrastructure Service Product Dept.)]

在 2022/11/12 0:35, Stefano Garzarella 写道:
> On Fri, Nov 11, 2022 at 11:49:10PM +0800, Longpeng (Mike, Cloud 
> Infrastructure Service Product Dept.) wrote:
> > 在 2022/11/11 23:14, Stefano Garzarella 写道:
> > > On Fri, Nov 11, 2022 at 10:55:05PM +0800, Longpeng(Mike) wrote:
> > > > From: Longpeng <longpeng2@xxxxxxxxxx>
> > > >
> > > > 1. We should not set status to 0 when invoking vp_vdpa_set_status().
> > > >
> > > > 2. The driver MUST wait for a read of device_status to return 0 before
> > > >   reinitializing the device.
> > > >
> > > > Signed-off-by: Longpeng <longpeng2@xxxxxxxxxx>
> > > > ---
> > > > drivers/vdpa/virtio_pci/vp_vdpa.c | 11 ++++++++++-
> > > > 1 file changed, 10 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c 
> > > > b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > > > index d448db0c4de3..d35fac5cde11 100644
> > > > --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> > > > +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > > > @@ -212,8 +212,12 @@ static void vp_vdpa_set_status(struct 
> > > > vdpa_device *vdpa, u8 status)
> > > > {
> > > >     struct vp_vdpa *vp_vdpa = vdpa_to_vp(vdpa);
> > > >     struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
> > > > -    u8 s = vp_vdpa_get_status(vdpa);
> > >
> > > Is this change really needed?
> > No need to get the status if we try to set status to 0 (trigger BUG).
>
> Okay, but that's the case that should never happen, so IMHO we can leave 
> it as it is.
OK.

> > > > +    u8 s;
> > > > +
> > > > +    /* We should never be setting status to 0. */
> > > > +    BUG_ON(status == 0);
> > >
> > > IMHO panicking the kernel seems excessive in this case, please use 
> > > WARN_ON and maybe return earlier.
> > Um...I referenced the vp_reset/vp_set_status,
>
> Ah I see, maybe it's an old code, because recently we always try to 
> avoid BUG_ON().
OK. The checkpatch.pl script also triggered a waring about it.
I'll use WARN_ON in next version.

> > > > +    s = vp_vdpa_get_status(vdpa);
> > > >     if (status & VIRTIO_CONFIG_S_DRIVER_OK &&
> > > >         !(s & VIRTIO_CONFIG_S_DRIVER_OK)) {
> > > >         vp_vdpa_request_irq(vp_vdpa);
> > > > @@ -229,6 +233,11 @@ static int vp_vdpa_reset(struct vdpa_device *vdpa)
> > > >     u8 s = vp_vdpa_get_status(vdpa);
> > > >
> > > >     vp_modern_set_status(mdev, 0);
> > > > +    /* After writing 0 to device_status, the driver MUST wait for a 
> > > > read of
> > > > +     * device_status to return 0 before reinitializing the device.
> > > > +     */
> > > > +    while (vp_modern_get_status(mdev))
> > > > +        msleep(1);
> > >
> > > Should we set a limit after which we give up? A malfunctioning device 
> > > could keep us here forever.
> > Yes, but the malfunctioning device maybe can not work anymore, how to 
> > handle it?
>
> Maybe we should set the status to broken, but in this case we could just 
> return an error if we couldn't reset it, how about that?
It can work, but it seems to violate the specification. Maybe we can 
also wait for other guys' suggestions and then decide how to handle the 
exception.

> Thanks,
> Stefano
>
> .