From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932120AbbFSNfF (ORCPT ); Fri, 19 Jun 2015 09:35:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33959 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753398AbbFSNez (ORCPT ); Fri, 19 Jun 2015 09:34:55 -0400 Date: Fri, 19 Jun 2015 15:34:52 +0200 From: "Michael S. Tsirkin" To: Paolo Bonzini 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 Message-ID: <20150619153248-mutt-send-email-mst@redhat.com> References: <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> <5583F28A.9080206@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5583F28A.9080206@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > Paolo Can we simply defer the next device_add using a hva until all IO completes? > >> 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 linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/ From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions Date: Fri, 19 Jun 2015 15:34:52 +0200 Message-ID: <20150619153248-mutt-send-email-mst@redhat.com> References: <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> <5583F28A.9080206@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Igor Mammedov , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, andrey@xdel.ru To: Paolo Bonzini Return-path: Received: from mx1.redhat.com ([209.132.183.28]:33959 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753398AbbFSNez (ORCPT ); Fri, 19 Jun 2015 09:34:55 -0400 Content-Disposition: inline In-Reply-To: <5583F28A.9080206@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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. > > Paolo Can we simply defer the next device_add using a hva until all IO completes? > >> 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