From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754131AbbFSQUl (ORCPT ); Fri, 19 Jun 2015 12:20:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54162 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205AbbFSQUc (ORCPT ); Fri, 19 Jun 2015 12:20:32 -0400 Date: Fri, 19 Jun 2015 18:20:28 +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: <20150619181845-mutt-send-email-mst@redhat.com> References: <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> <20150619153248-mutt-send-email-mst@redhat.com> <55843310.50403@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55843310.50403@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 05:19:44PM +0200, Paolo Bonzini wrote: > > > 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 No need to audit them all: defer device_add using an hva range until address_space_unmap drops using hvas in range drops reference count to 0. -- MST -- 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 18:20:28 +0200 Message-ID: <20150619181845-mutt-send-email-mst@redhat.com> References: <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> <20150619153248-mutt-send-email-mst@redhat.com> <55843310.50403@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]:54162 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205AbbFSQUc (ORCPT ); Fri, 19 Jun 2015 12:20:32 -0400 Content-Disposition: inline In-Reply-To: <55843310.50403@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Jun 19, 2015 at 05:19:44PM +0200, Paolo Bonzini wrote: > > > 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 No need to audit them all: defer device_add using an hva range until address_space_unmap drops using hvas in range drops reference count to 0. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in