Re: [PATCH 10/13] vfio: Make vfio_device_open() exclusive between group path and device cdev path

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On Tue, Feb 07, 2023 at 01:19:10PM +0000, Liu, Yi L wrote:
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Sent: Tuesday, February 7, 2023 9:13 PM
> > 
> > On Tue, Feb 07, 2023 at 12:35:48AM +0000, Tian, Kevin wrote:
> > > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> > > > Sent: Monday, February 6, 2023 11:51 PM
> > > >
> > > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > > > > Sent: Monday, February 6, 2023 11:11 PM
> > > > >
> > > > > On Mon, Feb 06, 2023 at 10:09:52AM +0000, Tian, Kevin wrote:
> > > > > > It's probably simpler if we always mark DMA owner with vfio_group
> > > > > > for the group path, no matter vfio type1 or iommufd compat is used.
> > > > > > This should avoid all the tricky corner cases between the two paths.
> > > > >
> > > > > Yes
> > > >
> > > > Then, we have two choices:
> > > >
> > > > 1) extend iommufd_device_bind() to allow a caller-specified DMA
> > marker
> > > > 2) claim DMA owner before calling iommufd_device_bind(), still need to
> > > >      extend iommufd_device_bind() to accept a flag to bypass DMA
> > owner
> > > > claim
> > > >
> > > > which one would be better? or do we have a third choice?
> > > >
> > >
> > > first one
> > 
> > Why can't this all be handled in vfio??
> 
> Are you preferring the second one? Surely VFIO can claim DMA owner
> by itself. But it is the vfio iommufd compat mode, so it still needs to call
> iommufd_device_bind(). And it should bypass DMA owner claim since
> it's already done.

No, I mean why can't vfio just call iommufd exactly once regardless of
what mode it is running in?

Jason



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