On Tue, 26 May 2020 12:53:31 -0300
Jason Gunthorpe <j...@ziepe.ca> wrote:

> On Tue, May 26, 2020 at 08:32:18AM -0600, Alex Williamson wrote:
> > > > Certainly there is no reason to optimize the fringe case of vfio
> > > > sleeping if there is and incorrect concurrnent attempt to disable the
> > > > a BAR.    
> > > 
> > > If fixup_user_fault() (which is always with ALLOW_RETRY && !RETRY_NOWAIT) 
> > > is
> > > the only path for the new fault(), then current way seems ok.  Not sure 
> > > whether
> > > this would worth a WARN_ON_ONCE(RETRY_NOWAIT) in the fault() to be clear 
> > > of
> > > that fact.  
> > 
> > Thanks for the discussion over the weekend folks.  Peter, I take it
> > you'd be satisfied if this patch were updated as:
> > 
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index aabba6439a5b..35bd7cd4e268 100644
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -1528,6 +1528,13 @@ static vm_fault_t vfio_pci_mmap_fault(struct 
> > vm_fault *vmf)
> >     struct vfio_pci_device *vdev = vma->vm_private_data;
> >     vm_fault_t ret = VM_FAULT_NOPAGE;
> >  
> > +   /*
> > +    * We don't expect to be called with NOWAIT and there are conflicting
> > +    * opinions on whether NOWAIT suggests we shouldn't wait for locks or
> > +    * just shouldn't wait for I/O.
> > +    */
> > +   WARN_ON_ONCE(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);  
> 
> I don't think this is right, this implies there is some reason this
> code fails with FAULT_FLAG_RETRY_NOWAIT - but it is fine as written,
> AFAICT

Ok, Peter said he's fine either way, I'll use the patch as originally
posted and include Peter's R-b.  Thanks,

Alex

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