Re: [PATCH 07/14] vfio: specify VFIO_DMA_UNMAP_FLAG_ALL to callback

[John Levon <levon@movementarian.org>]

On Thu, Apr 24, 2025 at 07:16:52PM +0200, Cédric Le Goater wrote:

> > Having said that I'm OK with going back to just a simple boolean if you'd really
> > prefer.
> 
> yes. VFIO_DMA_UNMAP_FLAG_ALL is a kernel interface and we don't
> need more than one flag today.

OK

> > > Why not unmap the halves here instead of in the backends ?
> > 
> > The whole point of the change is that right now the generic listener.c code has
> > a workaround that is specific to one particular backend.
> 
> It's due to the ARM IO space size AFAICT.
> 
> > vfio-user doesn't have
> > any need to unmap in halves and in fact *has* to pass an "unmap all" flag.
> 
> OK. So this flag is a vfio-user requirement. Why can't we call
> vfio_container_dma_unmap() twice from vfio_listener_region_del() ?

Are you suggesting that the vfio-user backend - and the protocol - somehow
accounts for the two unmaps and translates it back into an unmap all? How would
that work?

Surely it's very ugly indeed to embed a foible of the (old) vfio kernel
interface into every backend.

regards
john