? 2022/11/12 15:33, Longpeng (Mike, Cloud Infrastructure Service Product
Dept.) ??:>
>
> ? 2022/11/12 0:35, Stefano Garzarella ??:
>> On Fri, Nov 11, 2022 at 11:49:10PM +0800, Longpeng (Mike, Cloud
>> Infrastructure Service Product Dept.) wrote:
>>>
>>>
>>> ? 2022/11/11 23:14, Stefano Garzarella ??:
>>>> On Fri, Nov 11, 2022 at 10:55:05PM +0800, Longpeng(Mike) wrote:
>>>>> From: Longpeng <longpeng2 at huawei.com>
>>>>>
>>>>> 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 at huawei.com>
>>>>> ---
>>>>> 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.
Need more thought but it's not an issue that is introduced in this
patch, we can do optimization on top.
Probably a warning plus FAILED. Then at least the device can DOS the
driver which is good for hardening as well.
Thanks
>
>> Thanks,
>> Stefano
>>
>> .
>