Re: [RFC PATCH v1] virtio_pci: only store successfully populated virtio_pci_vq_info
From: Michael S. Tsirkin
Date: Tue Apr 21 2026 - 17:51:33 EST
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 <linkl@xxxxxxxxxx> 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 <linkl@xxxxxxxxxx>
> Co-developed-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
> Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxx/
same?
--
MST