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. Paolo >> device_add >> '-----------------------------------------> device_set_realized >> hotplug_handler_plug >> pc_machine_device_plug_cb >> pc_dimm_plug >> memory_region_add_subregion >> >> I/O finishes >> address_space_unmap >> >> Surprise removal similarly could be done in QEMU, but it will hold to >> some resources for as long as the device backends need them. >> >> Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
