Re: [RFC PATCH v1] virtio_pci: only store successfully populated virtio_pci_vq_info

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 21, 2026 at 03:15:55PM -0700, Link Lin wrote:
> Hi Michael,
> 
> That's essentially the same fix as ours but one month earlier. That's
> great news!
> 
> Quick follow-up question: Do you know if this will make it into v7.1?


I'll try.

> I also noticed the patch has the "Cc: stable@vger.kernel.org # v6.11+"
> tag, which is perfect since we actually hit this bug in v6.12.
> 
> I wasn't aware of Ammar's patch as I wasn't subscribed to the mailing
> list. Looks like we tried to reinvent the wheel ^_^;
> 
> Sincerely,
> Link
> 
> 
> On Tue, Apr 21, 2026 at 2:51 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Tue, Apr 21, 2026 at 02:47:32PM -0700, Link Lin wrote:
> > > Hi everyone,
> > >
> > > Friendly ping. Apologies if you are getting this the second time - my
> > > last ping wasn't in plain text mode and got rejected by some mailing
> > > lists.
> > >
> > > Please let me know if anyone has had a chance to look at this RFC
> > > patch, or if any changes are needed.
> > >
> > > Thanks,
> > > Link
> > >
> > > On Tue, Apr 21, 2026 at 2:24 PM Link Lin <linkl@google.com> 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@google.com> 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@google.com>
> > > >> Co-developed-by: Jiaqi Yan <jiaqiyan@google.com>
> > > >> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> > > >> ---
> > > >>  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?
> >
> >