Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754872AbbHYDEr (ORCPT ); Mon, 24 Aug 2015 23:04:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56953 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751084AbbHYDEq (ORCPT ); Mon, 24 Aug 2015 23:04:46 -0400 Message-ID: <55DBDB48.6060502@redhat.com> Date: Tue, 25 Aug 2015 11:04:40 +0800 From: Jason Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0 MIME-Version: 1.0 To: Cornelia Huck CC: gleb@kernel.org, pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, "Michael S. Tsirkin" Subject: Re: [PATCH 2/3] kvm: don't register wildcard MMIO EVENTFD on two buses References: <1440144233-29748-1-git-send-email-jasowang@redhat.com> <1440144233-29748-2-git-send-email-jasowang@redhat.com> <20150821112946.64ae6f7b.cornelia.huck@de.ibm.com> <55DA8F99.106@redhat.com> <20150824160520.583c3a74.cornelia.huck@de.ibm.com> In-Reply-To: <20150824160520.583c3a74.cornelia.huck@de.ibm.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 Content-Length: 3150 Lines: 81 On 08/24/2015 10:05 PM, Cornelia Huck wrote: > On Mon, 24 Aug 2015 11:29:29 +0800 > Jason Wang wrote: > >> On 08/21/2015 05:29 PM, Cornelia Huck wrote: >>> On Fri, 21 Aug 2015 16:03:52 +0800 >>> Jason Wang wrote: >>>> @@ -850,9 +845,15 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) >>> Unfortunately snipped by diff, but the check here is on !len && !PIO, >>> which only does the desired thing as VIRTIO_CCW always uses len == 8. >>> Should the check be for !len && MMIO instead? >> I think the answer depends on whether len == 0 is valid for ccw. If not >> we can fail the assign earlier. Since even without this patch, if >> userspace tries to register a dev with len equals to zero, it will also >> be registered to KVM_FAST_MMIO_BUS. If yes, we need check as you >> suggested here. > I don't think len != 8 makes much sense for the way ioeventfd is > defined for ccw (we handle hypercalls with a payload specifying the > device), but we currently don't actively fence it. > > But regardless, I'd prefer to decide directly upon whether userspace > actually tried to register for the mmio bus. Ok. > >>>> ret = kvm_io_bus_register_dev(kvm, KVM_FAST_MMIO_BUS, >>>> p->addr, 0, &p->dev); >>>> if (ret < 0) >>>> - goto register_fail; >>>> + goto unlock_fail; >>>> + } else { >>>> + ret = kvm_io_bus_register_dev(kvm, bus_idx, p->addr, p->length, >>>> + &p->dev); >>>> + if (ret < 0) >>>> + goto unlock_fail; >>>> } >>> Hm... maybe the following would be more obvious: >>> >>> my_bus = (p->length == 0) && (bus_idx == KVM_MMIO_BUS) ? KVM_FAST_MMIO_BUS : bus_idx; >>> ret = kvm_io_bus_register_dev(kvm, my_bus, p->addr, p->length, &pdev->dev); >>> >>>> >>>> + >>>> kvm->buses[bus_idx]->ioeventfd_count++; >>>> list_add_tail(&p->list, &kvm->ioeventfds); >>> (...) >>> >>>> @@ -900,10 +899,11 @@ kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) >>>> if (!p->wildcard && p->datamatch != args->datamatch) >>>> continue; >>>> >>>> - kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev); >>>> if (!p->length) { >>>> kvm_io_bus_unregister_dev(kvm, KVM_FAST_MMIO_BUS, >>>> &p->dev); >>>> + } else { >>>> + kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev); >>>> } >>> Similar comments here... do you want to check for bus_idx == >>> KVM_MMIO_BUS as well? >> Good catch. I think keep the original code as is will be also ok to >> solve this. (with changing the bus_idx to KVM_FAST_MMIO_BUS during >> registering if it was an wildcard mmio). > Do you need to handle the ioeventfd_count changes on the fast mmio bus > as well? Yes. So actually, it needs some changes: checking the return value of kvm_io_bus_unregister_dev() and decide which bus does the device belongs to. > >>>> kvm->buses[bus_idx]->ioeventfd_count--; >>>> ioeventfd_release(p); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/