On 19/06/2015 15:34, Michael S. Tsirkin wrote: > On Fri, Jun 19, 2015 at 12:44:26PM +0200, Paolo Bonzini wrote: >> >> >> On 19/06/2015 12:14, Michael S. Tsirkin wrote: >>> On Fri, Jun 19, 2015 at 10:52:47AM +0200, Paolo Bonzini wrote: >>>> >>>> >>>> On 19/06/2015 10:05, Michael S. Tsirkin wrote: >>>>>> No, only destruction of the memory region frees it. address_space_map >>>>>> takes a reference to the memory region and address_space_unmap releases >>>>>> it. >>>>>> >>>>>> Paolo >>>>> >>>>> Confused. So can we call mmap(MAP_NORESERVE) in address_space_unmap >>>>> after we detect refcount is 0? >>>> >>>> No, because in the meanwhile another DIMM could have been hotplugged >>>> at the same place where the old one was. This is legal: >>>> >>>> user guest QEMU >>>> >>>> ---------------------------------------------------------------------------------------- >>>> start I/O >>>> '---------------> address_space_map >>>> device_del >>>> '-------------------> receives SCI >>>> executes _EJ0 >>>> '---------------> >>>> memory_region_del_subregion >>>> object_unparent >>> >>> So guest started DMA into memory, then ejected this memory while DMA >>> is in progress? >> >> Yes. There is nothing that forbids doing that. > > Can we simply defer the next device_add using a hva until all IO completes?
We could, but I/O is just an example. It can be I/O, a network ring, whatever. We cannot audit all address_space_map uses. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
