Re: [PATCH vfio 10/11] vfio/virtio: Expose admin commands over virtio device

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On Tue, Oct 10, 2023 at 12:03:29PM -0400, Michael S. Tsirkin wrote:
> On Tue, Oct 10, 2023 at 12:59:37PM -0300, Jason Gunthorpe wrote:
> > On Tue, Oct 10, 2023 at 11:14:56AM -0400, Michael S. Tsirkin wrote:
> > 
> > > I suggest 3 but call it on the VF. commands will switch to PF
> > > internally as needed. For example, intel might be interested in exposing
> > > admin commands through a memory BAR of VF itself.
> > 
> > FWIW, we have been pushing back on such things in VFIO, so it will
> > have to be very carefully security justified.
> > 
> > Probably since that is not standard it should just live in under some
> > intel-only vfio driver behavior, not in virtio land.
> > 
> > It is also costly to switch between pf/vf, it should not be done
> > pointlessly on the fast path.
> > 
> > Jason
> 
> Currently, the switch seems to be just a cast of private data.
> I am suggesting keeping that cast inside virtio. Why is that
> expensive?

pci_iov_get_pf_drvdata() does a bunch of sanity checks and function
calls. It was not intended to be used on a fast path.

Jason 



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