Re: [PATCH 4/5] vfio: Introduce vfio_device_ops.get_unmapped_area hook

[Peter Xu <peterx@redhat.com>]

On Tue, Jun 17, 2025 at 12:47:35PM -0400, Peter Xu wrote:
> On Tue, Jun 17, 2025 at 12:41:57PM -0300, Jason Gunthorpe wrote:
> > On Tue, Jun 17, 2025 at 11:39:07AM -0400, Peter Xu wrote:
> > >  
> > > +#ifdef CONFIG_ARCH_SUPPORTS_HUGE_PFNMAP
> > >  static unsigned long vfio_device_get_unmapped_area(struct file *file,
> > >                                                    unsigned long addr,
> > >                                                    unsigned long len,
> > > @@ -1370,6 +1371,7 @@ static unsigned long vfio_device_get_unmapped_area(struct file *file,
> > >         return device->ops->get_unmapped_area(device, file, addr, len,
> > >                                               pgoff, flags);
> > >  }
> > > +#endif
> > >  
> > >  const struct file_operations vfio_device_fops = {
> > >         .owner          = THIS_MODULE,
> > > @@ -1380,7 +1382,9 @@ const struct file_operations vfio_device_fops = {
> > >         .unlocked_ioctl = vfio_device_fops_unl_ioctl,
> > >         .compat_ioctl   = compat_ptr_ioctl,
> > >         .mmap           = vfio_device_fops_mmap,
> > > +#ifdef CONFIG_ARCH_SUPPORTS_HUGE_PFNMAP
> > >         .get_unmapped_area = vfio_device_get_unmapped_area,
> > > +#endif
> > >  };
> > 
> > IMHO this also seems like something the core code should be dealing
> > with and not putting weird ifdefs in drivers.
> 
> It may depend on whether we want to still do the fallbacks to
> mm_get_unmapped_area().  I get your point in the other email but not yet
> get a chance to reply.  I'll try that out to see how it looks and reply
> there.

I just noticed this is unfortunate and special; I yet don't see a way to
avoid the fallback here.

Note that this is the vfio_device's fallback, even if the new helper
(whatever we name it..) could do fallback internally, vfio_device still
would need to be accessible to mm_get_unmapped_area() to make this config
build pass.

So I think I'll need my fixup here..

-- 
Peter Xu