From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932150AbdJUOeS (ORCPT ); Sat, 21 Oct 2017 10:34:18 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:50977 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932099AbdJUOeQ (ORCPT ); Sat, 21 Oct 2017 10:34:16 -0400 X-Google-Smtp-Source: ABhQp+T0r0ssZnH4a2BxPkgusus57n2EUWlnTFfZWQX6h9pvpQIxaftwAq/wB0ueBH5r/BY0EdfYUQ== Date: Sat, 21 Oct 2017 16:34:14 +0200 From: Christoffer Dall To: Auger Eric Cc: eric.auger.pro@gmail.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, marc.zyngier@arm.com, peter.maydell@linaro.org, andre.przywara@arm.com, wanghaibin.wang@huawei.com, wu.wubin@huawei.com Subject: Re: [PATCH v2 07/10] KVM: arm/arm64: vgic-its: new helper functions to free the caches Message-ID: <20171021143414.GA17884@cbox> References: <1506518920-18571-1-git-send-email-eric.auger@redhat.com> <1506518920-18571-8-git-send-email-eric.auger@redhat.com> <20171013133516.GJ8927@cbox> <48a4cb2e-81cd-4026-5f30-0a0a77d506f8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <48a4cb2e-81cd-4026-5f30-0a0a77d506f8@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 21, 2017 at 11:02:27AM +0200, Auger Eric wrote: > Hi Christoffer, > > On 13/10/2017 15:35, Christoffer Dall wrote: > > On Wed, Sep 27, 2017 at 03:28:37PM +0200, Eric Auger wrote: > >> From: wanghaibin > >> > >> We create 2 new functions that frees the device and > > > > two free > > > >> collection lists. this is currently called by vgic_its_destroy() > > > First my apologies as most of your comments have been left out of the > v3-v4 respin by oversight. Some comments below. > > > > These are > > > >> and we will add other callers in subsequent patches. > >> > >> We also remove the check on its->device_list.next as it looks > >> unnecessary: > > > > Could you elude to why you're doing this in the first place in the next > > version of the commit message? Thanks. > > > >> > >> The kvm device is removed by kvm_destroy_devices which loops on > >> all the devices added to kvm->devices. kvm_ioctl_create_device > >> only adds the device to kvm_devices once the lists have been > >> initialized (in vgic_create_its). > > > > I don't understand what this paragraph is trying to tell me beyond what > > some code already does irrelevant to this patch? > > > >> > >> We also move vgic_its_free_device to prepare for new callers. > >> > >> Signed-off-by: wanghaibin > >> Signed-off-by: Eric Auger > >> > >> --- > >> [Eric] removed its->device_list.next which is not needed as > >> pointed out by Wanghaibin. Reword the commit message > >> --- > >> virt/kvm/arm/vgic/vgic-its.c | 76 ++++++++++++++++++++++++-------------------- > >> 1 file changed, 41 insertions(+), 35 deletions(-) > >> > >> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c > >> index 9e6b556..0df6d5f 100644 > >> --- a/virt/kvm/arm/vgic/vgic-its.c > >> +++ b/virt/kvm/arm/vgic/vgic-its.c > >> @@ -611,6 +611,45 @@ static void its_free_ite(struct kvm *kvm, struct its_ite *ite) > >> kfree(ite); > >> } > >> > >> +static void vgic_its_free_device(struct kvm *kvm, struct its_device *dev) > >> +{ > >> + struct its_ite *ite, *tmp; > >> + > >> + list_for_each_entry_safe(ite, tmp, &dev->itt_head, ite_list) > >> + its_free_ite(kvm, ite); > >> + list_del(&dev->dev_list); > >> + kfree(dev); > >> +} > >> + > >> +static void vgic_its_free_device_list(struct kvm *kvm, struct vgic_its *its) > >> +{ > >> + struct list_head *cur, *temp; > >> + > >> + mutex_lock(&its->its_lock); > >> + list_for_each_safe(cur, temp, &its->device_list) { > >> + struct its_device *dev; > >> + > >> + dev = list_entry(cur, struct its_device, dev_list); > >> + vgic_its_free_device(kvm, dev); > >> + } > >> + mutex_unlock(&its->its_lock); > > > > > > this changes semantics from locking across freeing both devices and > > collections to taking the locks separately. Is that valid? > > Handling deletion of device and collection separately is valid I think > as MAPC (vgic_its_cmd_handle_mapc) and MAPD(vgic_its_cmd_handle_mapd) > commands do that separately. > > However, ..., a collection can be referred by an ITE and I should reset > the ite->collection = NULL for all ITEs referencing a deleted ITE. > vgic_its_free_collection do that. > > By the way, vgic_its_unmap_device() is same as vgic_its_free_device() so > I can remove vgic_its_free_device. > > > > > >> +} > >> + > >> +static void vgic_its_free_collection_list(struct kvm *kvm, struct vgic_its *its) > >> +{ > >> + struct list_head *cur, *temp; > >> + > >> + list_for_each_safe(cur, temp, &its->collection_list) { > >> + struct its_collection *coll; > >> + > >> + coll = list_entry(cur, struct its_collection, coll_list); > >> + list_del(cur); > >> + kfree(coll); > >> + } > >> + mutex_unlock(&its->its_lock); > > > > no mutex_lock ? > damned. > > > >> +} > >> + > >> + > >> static u64 its_cmd_mask_field(u64 *its_cmd, int word, int shift, int size) > >> { > >> return (le64_to_cpu(its_cmd[word]) >> shift) & (BIT_ULL(size) - 1); > >> @@ -1634,46 +1673,13 @@ static int vgic_its_create(struct kvm_device *dev, u32 type) > >> return vgic_its_set_abi(its, NR_ITS_ABIS - 1); > >> } > >> > >> -static void vgic_its_free_device(struct kvm *kvm, struct its_device *dev) > >> -{ > >> - struct its_ite *ite, *tmp; > >> - > >> - list_for_each_entry_safe(ite, tmp, &dev->itt_head, ite_list) > >> - its_free_ite(kvm, ite); > >> - list_del(&dev->dev_list); > >> - kfree(dev); > >> -} > >> - > >> static void vgic_its_destroy(struct kvm_device *kvm_dev) > >> { > >> struct kvm *kvm = kvm_dev->kvm; > >> struct vgic_its *its = kvm_dev->private; > >> - struct list_head *cur, *temp; > >> - > >> - /* > >> - * We may end up here without the lists ever having been initialized. > >> - * Check this and bail out early to avoid dereferencing a NULL pointer. > >> - */ > >> - if (!its->device_list.next) > >> - return; > > > > I don't think this is valid. We can actually have a non-initialized > > list and without this check, list_for_each_entry_safe in > > vgic_its_free_device_list will crash the kernel. > > I think you agreed on my previous statement: > https://www.spinics.net/lists/kvm-arm/msg27198.html > > > I understand the sequence is: > 1) vm_ioctl_create_device > |_ ops->create > |_ vgic_create_its > INIT_LIST_HEAD(&its->device_list); > INIT_LIST_HEAD(&its->collection_list); > list_add(&dev->vm_node, &kvm->devices); > > kvm_destroy_devices > list_for_each_entry_safe(dev, tmp, &kvm->devices, vm_node) { > ops->destroy > |_ vgic_its_destroy > > so vgic_its_destroy is called on an its device that was added to the > kvm->devices list. If so the list was created. > > Then we have vgic_mmio_write_its_baser() which is new caller introduced > in subsequent patch. > > for vgic_mmio_write_its_baser() to be called, vgic_register_its_iodev > must have been called. This latter is called on set_attr=vgic_its_set_attr > set_attr can be called only if the fd is created. This happens in > kvm_ioctl_create_device after ops->create() has been successful, ie > meaning the lists are created. > > What do I miss? What is the case you identified where the device_list is > not initialized? > I am probably just remembering incorrect, I just thought we identified some strange flow where this could happen, but I can't do that anymore, so I'll stop asking this question. Sorry about that. -Christoffer