Re: [RFC] /dev/ioasid uAPI proposal

[Alex Williamson]

On Fri, 4 Jun 2021 09:13:37 -0300
Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:

> On Thu, Jun 03, 2021 at 02:41:36PM -0600, Alex Williamson wrote:
> 
> > Could you clarify "vfio_driver"?    
> 
> This is the thing providing the vfio_device_ops function pointers.
> 
> So vfio-pci can't know anything about this (although your no-snoop
> control probing idea makes sense to me)
> 
> But vfio_mlx5_pci can know
> 
> So can mdev_idxd
> 
> And kvmgt

A capability on VFIO_DEVICE_GET_INFO could provide a hint to userspace.
Stock vfio-pci could fill it out to the extent advertising if the
device is capable of non-coherent DMA based on the Enable No-snoop
probing, the device specific vfio_drivers could set it based on
knowledge of the device behavior.  Another bit might indicate a
preference to not suppress non-coherent DMA at the IOMMU.  Thanks,

Alex