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[80.230.25.21]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488fb755938sm167530455e9.3.2026.04.21.15.16.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 15:16:51 -0700 (PDT) Date: Tue, 21 Apr 2026 18:16:49 -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, ammarfaizi2@openresty.com Subject: Re: [RFC PATCH v1] virtio_pci: only store successfully populated virtio_pci_vq_info Message-ID: <20260421181640-mutt-send-email-mst@kernel.org> References: <20260407212521.934620-1-linkl@google.com> <20260421175107-mutt-send-email-mst@kernel.org> 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: 1Lny6ZtskZ_eudnjNQlSZbwt5Mxu5U_iZmsLSvmCRrI_1776809813 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 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 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 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? > > > >