From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions Date: Fri, 19 Jun 2015 10:52:47 +0200 Message-ID: <5583D85F.7090200@redhat.com> References: <20150618112004-mutt-send-email-mst@redhat.com> <20150618133912.63636a47@nial.brq.redhat.com> <20150618134040-mutt-send-email-mst@redhat.com> <5582B088.1090207@redhat.com> <20150618142455-mutt-send-email-mst@redhat.com> <5582CBA6.5070105@redhat.com> <20150618164559-mutt-send-email-mst@redhat.com> <5582EBA6.1080607@redhat.com> <20150619095515-mutt-send-email-mst@redhat.com> <5583CB62.6030405@redhat.com> <20150619100409-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Cc: Igor Mammedov , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, andrey@xdel.ru To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20150619100409-mutt-send-email-mst@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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 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