From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754654AbbFSKoj (ORCPT ); Fri, 19 Jun 2015 06:44:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48568 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311AbbFSKoa (ORCPT ); Fri, 19 Jun 2015 06:44:30 -0400 Message-ID: <5583F28A.9080206@redhat.com> Date: Fri, 19 Jun 2015 12:44:26 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: Igor Mammedov , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, andrey@xdel.ru Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions References: <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> <5583D85F.7090200@redhat.com> <20150619120734-mutt-send-email-mst@redhat.com> In-Reply-To: <20150619120734-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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