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[80.230.25.21]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43fe4e4d5b1sm44523269f8f.30.2026.04.21.14.50.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 14:50:07 -0700 (PDT) Date: Tue, 21 Apr 2026 17:50:04 -0400 From: "Michael S. Tsirkin" To: Link Lin Cc: jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, jiaqiyan@google.com, rientjes@google.com, weixugc@google.com, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v1] virtio_pci: only store successfully populated virtio_pci_vq_info Message-ID: <20260421174945-mutt-send-email-mst@kernel.org> References: <20260407212521.934620-1-linkl@google.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 7S5dpxvo5Qni9brlzFYD0hHCPdb-7BW9NWDgJ6lcTNA_1776808208 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Tue, Apr 21, 2026 at 02:24:16PM -0700, Link Lin wrote: > Hi everyone, > > Friendly ping on this RFC patch. Please let me know if anyone has had a chance > to look at this, or if any changes are needed. > > Thanks, > Link > > On Tue, Apr 7, 2026 at 2:25 PM Link Lin wrote: > > In environments where free page reporting is disabled, a kernel > panic is triggered when tearing down the virtio_balloon module: > >   [12261.808190] Call trace: >   [12261.808471]  __list_del_entry_valid_or_report+0x18/0xe0 >   [12261.809064]  vp_del_vqs+0x12c/0x270 >   [12261.809462]  remove_common+0x80/0x98 [virtio_balloon] >   [12261.810034]  virtballoon_remove+0xfc/0x158 [virtio_balloon] >   [12261.810663]  virtio_dev_remove+0x68/0xf8 >   [12261.811108]  device_release_driver_internal+0x17c/0x278 >   [12261.811701]  driver_detach+0xd4/0x138 >   [12261.812117]  bus_remove_driver+0x90/0xd0 >   [12261.812562]  driver_unregister+0x40/0x70 >   [12261.813006]  unregister_virtio_driver+0x20/0x38 >   [12261.813518]  cleanup_module+0x20/0x7a8 [virtio_balloon] >   [12261.814109]  __arm64_sys_delete_module+0x278/0x3d0 >   [12261.814654]  invoke_syscall+0x5c/0x120 >   [12261.815086]  el0_svc_common+0x90/0xf8 >   [12261.815506]  do_el0_svc+0x2c/0x48 >   [12261.815883]  el0_svc+0x3c/0xa8 >   [12261.816235]  el0t_64_sync_handler+0x8c/0x108 >   [12261.816724]  el0t_64_sync+0x198/0x1a0 > > The issue originates in vp_find_vqs_intx(). It kzalloc_objs() based > on the nvqs count provided by the caller, virtio_balloon::init_vqs(). > However, it is not always the case that all nvqs number of > virtio_pci_vq_info objects will be properly populated. > > For example, when VIRTIO_BALLOON_F_FREE_PAGE_HINT is absent, the > VIRTIO_BALLOON_VQ_FREE_PAGE-th item in the vp_dev->vqs array is > actually never populated, and is still a zeroe-initialized > virtio_pci_vq_info object, which is eventually going to trigger > a __list_del_entry_valid_or_report() crash. > > Tested by applying this patch to a guest VM kernel with the > VIRTIO_BALLOON_F_REPORTING feature enabled and the > VIRTIO_BALLOON_F_FREE_PAGE_HINT feature disabled. > Without this patch, unloading the virtio_balloon module triggers a panic. > With this patch, no panic is observed. > > The fix is to use queue_idx to handle the case that vp_find_vqs_intx() > skips vp_setup_vq() when caller provided null vqs_info[i].name, when > the caller doesn't populate all nvqs number of virtqueue_info objects. > Invariantly queue_idx is the correct index to store a successfully > created and populated virtio_pci_vq_info object. As a result, now > a virtio_pci_device object only stores queue_idx number of valid > virtio_pci_vq_info objects in its vqs array when the for-loop over > nvqs finishes (of course, without goto out_del_vqs). > > vp_find_vqs_msix() has similar issue, so fix it in the same way. > > This patch is marked as RFC because we are uncertain if any virtio-pci > code implicitly requires virtio_pci_device's vqs array to always > contain nvqs number of virtio_pci_vq_info objects, and to store > zero-initialized virtio_pci_vq_info objects. We have not observed > any issues in our testing, but insights or alternatives are welcome! > > Signed-off-by: Link Lin > Co-developed-by: Jiaqi Yan > Signed-off-by: Jiaqi Yan > --- >  drivers/virtio/virtio_pci_common.c | 10 ++++++---- >  1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/ > virtio_pci_common.c > index da97b6a988de..9b32301529e5 100644 > --- a/drivers/virtio/virtio_pci_common.c > +++ b/drivers/virtio/virtio_pci_common.c > @@ -423,14 +423,15 @@ static int vp_find_vqs_msix(struct virtio_device > *vdev, unsigned int nvqs, >                         vqs[i] = NULL; >                         continue; >                 } > -               vqs[i] = vp_find_one_vq_msix(vdev, queue_idx++, vqi-> > callback, > +               vqs[i] = vp_find_one_vq_msix(vdev, queue_idx, vqi-> > callback, >                                              vqi->name, vqi->ctx, false, >                                              &allocated_vectors, > vector_policy, > -                                            &vp_dev->vqs[i]); > +                                            &vp_dev->vqs[queue_idx]); >                 if (IS_ERR(vqs[i])) { >                         err = PTR_ERR(vqs[i]); >                         goto error_find; >                 } > +               ++queue_idx; >         } > >         if (!avq_num) > @@ -485,13 +486,14 @@ static int vp_find_vqs_intx(struct virtio_device > *vdev, unsigned int nvqs, >                         vqs[i] = NULL; >                         continue; >                 } > -               vqs[i] = vp_setup_vq(vdev, queue_idx++, vqi->callback, > +               vqs[i] = vp_setup_vq(vdev, queue_idx, vqi->callback, >                                      vqi->name, vqi->ctx, > -                                    VIRTIO_MSI_NO_VECTOR, &vp_dev->vqs > [i]); > +                                    VIRTIO_MSI_NO_VECTOR, &vp_dev->vqs > [queue_idx]); >                 if (IS_ERR(vqs[i])) { >                         err = PTR_ERR(vqs[i]); >                         goto out_del_vqs; >                 } > +               ++queue_idx; >         } > >         if (!avq_num) > -- > 2.53.0.1213.gd9a14994de-goog > I have this in my tree: https://lore.kernel.org/all/20260315141808.547081-1-ammarfaizi2@openresty.com/ same? -- MST