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 Jason
