Re: [PATCH v2 6/6] vfio: platform: move get/put reset at open/release

Arnd Bergmann
2015-10-22T14:10:06Z

On Thursday 22 October 2015 15:26:55 Eric Auger wrote:
> >> @@ -181,6 +182,8 @@ static int vfio_platform_open(void *device_data)
> >> if (ret)
> >> goto err_irq;
> >>
> >> + vfio_platform_get_reset(vdev);
> >> +
> >> if (vdev->reset)
> >> vdev->reset(vdev);
> >>
> >
> > This needs some error handling to ensure that the open() fails
> > if there is no reset handler.
>
> Is that really what we want? The code was meant to allow the use case
> where the VFIO platform driver would be used without such reset module.
>
> I think the imperious need for a reset module depends on the device and
> more importantly depends on the IOMMU mapping. With QEMU VFIO
> integration this is needed because the whole VM memory is IOMMU mapped
> but in a simpler user-space driver context, we might live without.
>
> Any thought?

I would think we need a reset driver for any device that can start DMA,
otherwise things can go wrong as soon as you attach it to a different domain
while there is ongoing DMA.

Maybe we could just allow devices to be attached without a reset handler,
but then disallow DMA on them?

Arnd