On 11/4/19 1:15 PM, Jason Gunthorpe wrote: ... >> Right, and I thought about this when converting, and realized that the above >> code is working around the current gup.c limitations, which are "cannot >> support >> gup remote with FOLL_LONGTERM". > > But AFAICT it doesn't have a problem, the protection test is just too > strict, and I guess the control flow needs a bit of fixing.. > > The issue is this: > > static __always_inline long __get_user_pages_locked(): > { > if (locked) { > /* if VM_FAULT_RETRY can be returned, vmas become invalid */ > BUG_ON(vmas); > /* check caller initialized locked */ > BUG_ON(*locked != 1); > } > > > so remote could be written as: > > if (gup_flags & FOLL_LONGTERM) { > if (WARN_ON_ONCE(locked)) > return -EINVAL; > return __gup_longterm_locked(...) > } > > return __get_user_pages_locked(...) > > ??
Yes, that loosens it up just enough for the vfio case (which doesn't set "locked") to get through, great! OK, I'll put that (the above plus corresponding vfio fix) in a separate patch first. This should clear things up nicely. thanks, -- John Hubbard NVIDIA