| Message ID | 20221220141449.115918-3-hengqi@linux.alibaba.com (mailing list archive) |
|---|---|
| State | Deferred |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | virtio_net: support multi buffer xdp | expand |
在 2022/12/20 22:14, Heng Qi 写道: > When the xdp program sets xdp.frags, which means it can process > multi-buffer packets over larger MTU, so we continue to support xdp. > But for single-buffer xdp, we should keep checking for MTU. > > Signed-off-by: Heng Qi <hengqi@linux.alibaba.com> > Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> > --- > drivers/net/virtio_net.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 443aa7b8f0ad..c5c4e9db4ed3 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -3095,8 +3095,8 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog, > return -EINVAL; > } > > - if (dev->mtu > max_sz) { > - NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP"); > + if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) { Not related to this patch, but I see: unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr); Which is suspicious, do we need to count reserved headroom/tailroom as well? Thanks > + NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP without frags"); > netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz); > return -EINVAL; > }
在 2022/12/27 下午2:32, Jason Wang 写道: > > 在 2022/12/20 22:14, Heng Qi 写道: >> When the xdp program sets xdp.frags, which means it can process >> multi-buffer packets over larger MTU, so we continue to support xdp. >> But for single-buffer xdp, we should keep checking for MTU. >> >> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com> >> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> >> --- >> drivers/net/virtio_net.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 443aa7b8f0ad..c5c4e9db4ed3 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -3095,8 +3095,8 @@ static int virtnet_xdp_set(struct net_device >> *dev, struct bpf_prog *prog, >> return -EINVAL; >> } >> - if (dev->mtu > max_sz) { >> - NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP"); >> + if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) { > > > Not related to this patch, but I see: > > unsigned long int max_sz = PAGE_SIZE - sizeof(struct > padded_vnet_hdr); > > Which is suspicious, do we need to count reserved headroom/tailroom as > well? This seems to be suspicious. After loading xdp, the size of the filled avail buffer is (PAGE_SIZE - headroom - tailroom), so the size of the received used buffer, ie MTU, should also be (PAGE_SIZE - headroom - tailroom). Thanks. > > Thanks > > >> + NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP >> without frags"); >> netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz); >> return -EINVAL; >> }
在 2022/12/27 下午8:20, Heng Qi 写道: > > > 在 2022/12/27 下午2:32, Jason Wang 写道: >> >> 在 2022/12/20 22:14, Heng Qi 写道: >>> When the xdp program sets xdp.frags, which means it can process >>> multi-buffer packets over larger MTU, so we continue to support xdp. >>> But for single-buffer xdp, we should keep checking for MTU. >>> >>> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com> >>> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> >>> --- >>> drivers/net/virtio_net.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>> index 443aa7b8f0ad..c5c4e9db4ed3 100644 >>> --- a/drivers/net/virtio_net.c >>> +++ b/drivers/net/virtio_net.c >>> @@ -3095,8 +3095,8 @@ static int virtnet_xdp_set(struct net_device >>> *dev, struct bpf_prog *prog, >>> return -EINVAL; >>> } >>> - if (dev->mtu > max_sz) { >>> - NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP"); >>> + if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) { >> >> >> Not related to this patch, but I see: >> >> unsigned long int max_sz = PAGE_SIZE - sizeof(struct >> padded_vnet_hdr); >> >> Which is suspicious, do we need to count reserved headroom/tailroom >> as well? > > This seems to be suspicious. After loading xdp, the size of the filled > avail buffer > is (PAGE_SIZE - headroom - tailroom), so the size of the received used > buffer, ie MTU, > should also be (PAGE_SIZE - headroom - tailroom). Hi Jason, this is indeed a problem. After verification, packet drop will indeed occur. To avoid this, the size of MTU should be (PAGE_SIZE - headroom - tailroom - ethhdr = 4096 - 256 -320 - 14 =3506). Because when there is xdp, each filling is 3520 (PAGE_SIZE - room), if the value of (MTU + 14) is greater than 3520 (because the MTU does not contain the ethernet header), then the packet with a length greater than 3520 will come in, so num_buf will still be greater than or equal to 2, and then xdp_linearize_page() will be performed and the packet will be dropped because the total length is greater than PAGE_SIZE. I will make a separate bugfix patch to fix this later. Thanks. > > Thanks. > >> >> Thanks >> >> >>> + NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP >>> without frags"); >>> netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz); >>> return -EINVAL; >>> }
在 2022/12/28 11:50, Heng Qi 写道: > > > 在 2022/12/27 下午8:20, Heng Qi 写道: >> >> >> 在 2022/12/27 下午2:32, Jason Wang 写道: >>> >>> 在 2022/12/20 22:14, Heng Qi 写道: >>>> When the xdp program sets xdp.frags, which means it can process >>>> multi-buffer packets over larger MTU, so we continue to support xdp. >>>> But for single-buffer xdp, we should keep checking for MTU. >>>> >>>> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com> >>>> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> >>>> --- >>>> drivers/net/virtio_net.c | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>>> index 443aa7b8f0ad..c5c4e9db4ed3 100644 >>>> --- a/drivers/net/virtio_net.c >>>> +++ b/drivers/net/virtio_net.c >>>> @@ -3095,8 +3095,8 @@ static int virtnet_xdp_set(struct net_device >>>> *dev, struct bpf_prog *prog, >>>> return -EINVAL; >>>> } >>>> - if (dev->mtu > max_sz) { >>>> - NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP"); >>>> + if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) { >>> >>> >>> Not related to this patch, but I see: >>> >>> unsigned long int max_sz = PAGE_SIZE - sizeof(struct >>> padded_vnet_hdr); >>> >>> Which is suspicious, do we need to count reserved headroom/tailroom >>> as well? >> >> This seems to be suspicious. After loading xdp, the size of the >> filled avail buffer >> is (PAGE_SIZE - headroom - tailroom), so the size of the received >> used buffer, ie MTU, >> should also be (PAGE_SIZE - headroom - tailroom). > > Hi Jason, this is indeed a problem. After verification, packet drop > will indeed occur. To avoid this, > the size of MTU should be (PAGE_SIZE - headroom - tailroom - ethhdr = > 4096 - 256 -320 - 14 =3506). > Because when there is xdp, each filling is 3520 (PAGE_SIZE - room), if > the value of (MTU + 14) is > greater than 3520 (because the MTU does not contain the ethernet > header), then the packet with a > length greater than 3520 will come in, so num_buf will still be > greater than or equal to 2, and then > xdp_linearize_page() will be performed and the packet will be dropped > because the total length is > greater than PAGE_SIZE. > > I will make a separate bugfix patch to fix this later. Great. Thanks > > Thanks. > >> >> Thanks. >> >>> >>> Thanks >>> >>> >>>> + NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP >>>> without frags"); >>>> netdev_warn(dev, "XDP requires MTU less than %lu\n", >>>> max_sz); >>>> return -EINVAL; >>>> } >
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 443aa7b8f0ad..c5c4e9db4ed3 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -3095,8 +3095,8 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog, return -EINVAL; } - if (dev->mtu > max_sz) { - NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP"); + if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) { + NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP without frags"); netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz); return -EINVAL; }