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[79.183.34.164]) by smtp.gmail.com with ESMTPSA id t7sm19125131qkm.136.2020.01.05.03.16.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Jan 2020 03:16:36 -0800 (PST) Date: Sun, 5 Jan 2020 06:16:30 -0500 From: "Michael S. Tsirkin" To: Jason Wang Cc: Alistair Delva , Willem de Bruijn , LKML , "David S. Miller" , virtualization@lists.linux-foundation.org, Network Development Subject: Re: [PATCH net] virtio_net: CTRL_GUEST_OFFLOADS depends on CTRL_VQ Message-ID: <20200105061532-mutt-send-email-mst@kernel.org> References: <20191223140322.20013-1-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Dec 24, 2019 at 10:49:13AM +0800, Jason Wang wrote: > > On 2019/12/24 上午4:21, Alistair Delva wrote: > > On Mon, Dec 23, 2019 at 12:12 PM Willem de Bruijn > > wrote: > > > On Mon, Dec 23, 2019 at 2:56 PM Willem de Bruijn > > > wrote: > > > > 00fffe0ff0 DR7: 0000000000000400 > > > > > > Call Trace: > > > > > > ? preempt_count_add+0x58/0xb0 > > > > > > ? _raw_spin_lock_irqsave+0x36/0x70 > > > > > > ? _raw_spin_unlock_irqrestore+0x1a/0x40 > > > > > > ? __wake_up+0x70/0x190 > > > > > > virtnet_set_features+0x90/0xf0 [virtio_net] > > > > > > __netdev_update_features+0x271/0x980 > > > > > > ? nlmsg_notify+0x5b/0xa0 > > > > > > dev_disable_lro+0x2b/0x190 > > > > > > ? inet_netconf_notify_devconf+0xe2/0x120 > > > > > > devinet_sysctl_forward+0x176/0x1e0 > > > > > > proc_sys_call_handler+0x1f0/0x250 > > > > > > proc_sys_write+0xf/0x20 > > > > > > __vfs_write+0x3e/0x190 > > > > > > ? __sb_start_write+0x6d/0xd0 > > > > > > vfs_write+0xd3/0x190 > > > > > > ksys_write+0x68/0xd0 > > > > > > __ia32_sys_write+0x14/0x20 > > > > > > do_fast_syscall_32+0x86/0xe0 > > > > > > entry_SYSENTER_compat+0x7c/0x8e > > > > > > > > > > > > A similar crash will likely trigger when enabling XDP. > > > > > > > > > > > > Reported-by: Alistair Delva > > > > > > Reported-by: Willem de Bruijn > > > > > > Fixes: 3f93522ffab2 ("virtio-net: switch off offloads on demand if possible on XDP set") > > > > > > Signed-off-by: Michael S. Tsirkin > > > > > > --- > > > > > > > > > > > > Lightly tested. > > > > > > > > > > > > Alistair, could you please test and confirm that this resolves the > > > > > > crash for you? > > > > > This patch doesn't work. The reason is that NETIF_F_LRO is also turned > > > > > on by TSO4/TSO6, which your patch didn't check for. So it ends up > > > > > going through the same path and crashing in the same way. > > > > > > > > > > if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) || > > > > > virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6)) > > > > > dev->features |= NETIF_F_LRO; > > > > > > > > > > It sounds like this patch is fixing something slightly differently to > > > > > my patch fixed. virtnet_set_features() doesn't care about > > > > > GUEST_OFFLOADS, it only tests against NETIF_F_LRO. Even if "offloads" > > > > > is zero, it will call virtnet_set_guest_offloads(), which triggers the > > > > > crash. > > > > > > > > Interesting. It's surprising that it is trying to configure a flag > > > > that is not configurable, i.e., absent from dev->hw_features > > > > after Michael's change. > > > > > > > > > So either we need to ensure NETIF_F_LRO is never set, or > > > > LRO might be available, just not configurable. Indeed this was what I > > > > observed in the past. > > > dev_disable_lro expects that NETIF_F_LRO is always configurable. Which > > > I guess is a reasonable assumption, just not necessarily the case in > > > virtio_net. > > > > > > So I think we need both patches. Correctly mark the feature as fixed > > > by removing from dev->hw_features and also ignore the request from > > > dev_disable_lro, which does not check for this. > > Something like this maybe: > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index 4d7d5434cc5d..0556f42b0fb5 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -2560,6 +2560,9 @@ static int virtnet_set_features(struct net_device *dev, > > u64 offloads; > > int err; > > > > + if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)) > > + return 0; > > + > > if ((dev->features ^ features) & NETIF_F_LRO) { > > if (vi->xdp_queue_pairs) > > return -EBUSY; > > @@ -2971,6 +2974,15 @@ static int virtnet_validate(struct virtio_device *vdev) > > if (!virtnet_validate_features(vdev)) > > return -EINVAL; > > > > + /* VIRTIO_NET_F_CTRL_GUEST_OFFLOADS does not work without > > + * VIRTIO_NET_F_CTRL_VQ. However the virtio spec does not > > + * specify that VIRTIO_NET_F_CTRL_GUEST_OFFLOADS depends > > + * on VIRTIO_NET_F_CTRL_VQ so devices can set the later but > > + * not the former. > > + */ > > + if (!virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ)) > > + __virtio_clear_bit(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS); > > + > > if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) { > > int mtu = virtio_cread16(vdev, > > offsetof(struct virtio_net_config, > > > > We check feature dependency and fail the probe in > virtnet_validate_features(). > > Is it more straightforward to fail the probe there when CTRL_GUEST_OFFLOADS > was set but CTRL_VQ wasn't? > > Thanks Expanding on what the comment above says, we can't fail probe in this configuration without breaking the driver for spec compliant devices. -- MST