From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754064AbbFSQo4 (ORCPT ); Fri, 19 Jun 2015 12:44:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36759 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751710AbbFSQot (ORCPT ); Fri, 19 Jun 2015 12:44:49 -0400 Message-ID: <558446FC.6080301@redhat.com> Date: Fri, 19 Jun 2015 18:44:44 +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: <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> <20150619181845-mutt-send-email-mst@redhat.com> <558442B3.2020900@redhat.com> <20150619183226-mutt-send-email-mst@redhat.com> In-Reply-To: <20150619183226-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/06/2015 18:33, Michael S. Tsirkin wrote: > On Fri, Jun 19, 2015 at 06:26:27PM +0200, Paolo Bonzini wrote: >> >> >> On 19/06/2015 18:20, Michael S. Tsirkin wrote: >>>> 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. >>>> >>> >>> 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. >> >> That could be forever. You certainly don't want to lockup the monitor >> forever just because a device model isn't too friendly to memory hot-unplug. > > We can defer the addition, no need to lockup the monitor. Patches are welcome. >> That's why you need to audit them (also, it's perfectly in the device >> model's right to use address_space_unmap this way: it's the guest that's >> buggy and leaves a dangling reference to a region before unplugging it). > > Then maybe it's not too bad that the guest will crash because the memory > was unmapped. That's a matter of taste. I strongly prefer using 12K extra memory per VCPU to a guest crash. 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: Paolo Bonzini Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions Date: Fri, 19 Jun 2015 18:44:44 +0200 Message-ID: <558446FC.6080301@redhat.com> References: <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> <20150619181845-mutt-send-email-mst@redhat.com> <558442B3.2020900@redhat.com> <20150619183226-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Igor Mammedov , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, andrey@xdel.ru To: "Michael S. Tsirkin" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36759 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751710AbbFSQot (ORCPT ); Fri, 19 Jun 2015 12:44:49 -0400 In-Reply-To: <20150619183226-mutt-send-email-mst@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 19/06/2015 18:33, Michael S. Tsirkin wrote: > On Fri, Jun 19, 2015 at 06:26:27PM +0200, Paolo Bonzini wrote: >> >> >> On 19/06/2015 18:20, Michael S. Tsirkin wrote: >>>> 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. >>>> >>> >>> 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. >> >> That could be forever. You certainly don't want to lockup the monitor >> forever just because a device model isn't too friendly to memory hot-unplug. > > We can defer the addition, no need to lockup the monitor. Patches are welcome. >> That's why you need to audit them (also, it's perfectly in the device >> model's right to use address_space_unmap this way: it's the guest that's >> buggy and leaves a dangling reference to a region before unplugging it). > > Then maybe it's not too bad that the guest will crash because the memory > was unmapped. That's a matter of taste. I strongly prefer using 12K extra memory per VCPU to a guest crash. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in