qemu-kvm XDP forwarding with virtio_net

qemu-kvm XDP forwarding with virtio_net

[Pavel Popa]

Hi all,

I've implemented a XDP forwarding program using the bpf_fib_lookup()
helper, and loaded it in the kernel as XDP driver mode (i.e. executed
at the virtio_net driver level). The only problem is that the
receiving virtio network interface seems to drop the XDP packet after
successfully executing my XDP program.
Kernel: 4.18.10

my_xdp_fwd_kern.c:
/* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
BPF_FIB_LOOKUP_DIRECT);
/* made sure this returns 4 (i.e. XDP_REDIRECT) */
rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
return rc;

I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
is the correct dev index from FIB lookup.
dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
for (i = 1; i < 64; i++)
    bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);

I'm passing the following to the qemu cmd line for the 2 devices I
want to run XDP on (as stated here
https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
-device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
\
-device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
\

In the guest enabling also the MultiQueue feature, as stated here
https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
What I'm left with is debugging the virtio_net kernel module by adding
a bunch of printk() and see what happens, especially here
https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.

Am I doing something wrong here? What I'm missing?

Re: qemu-kvm XDP forwarding with virtio_net

[David Ahern]

On 11/20/18 7:18 AM, Pavel Popa wrote:
> Hi all,
> 
> I've implemented a XDP forwarding program using the bpf_fib_lookup()
> helper, and loaded it in the kernel as XDP driver mode (i.e. executed
> at the virtio_net driver level). The only problem is that the
> receiving virtio network interface seems to drop the XDP packet after
> successfully executing my XDP program.
> Kernel: 4.18.10
> 
> my_xdp_fwd_kern.c:
> /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
> rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> BPF_FIB_LOOKUP_DIRECT);
> /* made sure this returns 4 (i.e. XDP_REDIRECT) */
> rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
> return rc;
> 
> I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
> is the correct dev index from FIB lookup.
> dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
> for (i = 1; i < 64; i++)
>     bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
> 
> I'm passing the following to the qemu cmd line for the 2 devices I
> want to run XDP on (as stated here
> https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> \
> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> \
> 
> In the guest enabling also the MultiQueue feature, as stated here
> https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
> What I'm left with is debugging the virtio_net kernel module by adding
> a bunch of printk() and see what happens, especially here
> https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
> 
> Am I doing something wrong here? What I'm missing?
> 

I believe at this point you can drop the gso,tso,ufo and ecn args. I use
virtio for development and these days start my VMs with only:

...,mq=on,guest_csum=off,...

After that are you installing the xdp program on all interfaces that can
be used for forwarding? ie., if it transmits a packet in XDP mode it
needs the xdp program loaded. For example I use:

xdp_fwd eth1 eth2 eth3 eth4


From there:

echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
cat /sys/kernel/debug/tracing/trace_pipe

Re: qemu-kvm XDP forwarding with virtio_net

[Pavel Popa]

Well, here's the output from the `ip link` cmd:
    3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq
state UP mode DEFAULT group default qlen 1000
        link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
        prog/xdp id 1 tag 1cd982ef22273bda jited
    4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq
state UP mode DEFAULT group default qlen 1000
        link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
        prog/xdp id 1 tag 1cd982ef22273bda jited

As you can see, there's the XDP program ID 1 executing on them.
However, there's definitely something interesting happening when
bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
program just returns XDP_PASS while the following line gets printed in
kern.log:
    eth3: bad gso: type: 164, size: 256

No idea what's wrong here.
Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
which my XDP program executes bpf_redirect_map(&dev_map,
fib_params.ifindex, 0), the following gets printed in
/sys/kernel/debug/tracing/trace_pipe:
    xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
to_ifindex=0 err=-14 map_id=0 map_index=4

I feel this last one to be somewhat related to the comment here
https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
Is it correct? If so, what does this precisely mean? Is there any way
to get around with this? Because what I'm doing is simply using the
BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
packets between "XDP ports".

Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
<dsahern@gmail.com> ha scritto:
>
> On 11/20/18 7:18 AM, Pavel Popa wrote:
> > Hi all,
> >
> > I've implemented a XDP forwarding program using the bpf_fib_lookup()
> > helper, and loaded it in the kernel as XDP driver mode (i.e. executed
> > at the virtio_net driver level). The only problem is that the
> > receiving virtio network interface seems to drop the XDP packet after
> > successfully executing my XDP program.
> > Kernel: 4.18.10
> >
> > my_xdp_fwd_kern.c:
> > /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
> > rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> > BPF_FIB_LOOKUP_DIRECT);
> > /* made sure this returns 4 (i.e. XDP_REDIRECT) */
> > rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
> > return rc;
> >
> > I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
> > is the correct dev index from FIB lookup.
> > dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
> > for (i = 1; i < 64; i++)
> >     bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
> >
> > I'm passing the following to the qemu cmd line for the 2 devices I
> > want to run XDP on (as stated here
> > https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
> > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > \
> > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > \
> >
> > In the guest enabling also the MultiQueue feature, as stated here
> > https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
> > What I'm left with is debugging the virtio_net kernel module by adding
> > a bunch of printk() and see what happens, especially here
> > https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
> >
> > Am I doing something wrong here? What I'm missing?
> >
>
> I believe at this point you can drop the gso,tso,ufo and ecn args. I use
> virtio for development and these days start my VMs with only:
>
> ...,mq=on,guest_csum=off,...
>
> After that are you installing the xdp program on all interfaces that can
> be used for forwarding? ie., if it transmits a packet in XDP mode it
> needs the xdp program loaded. For example I use:
>
> xdp_fwd eth1 eth2 eth3 eth4
>
>
> From there:
>
> echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
> cat /sys/kernel/debug/tracing/trace_pipe
>

Re: qemu-kvm XDP forwarding with virtio_net

[Jesper Dangaard Brouer]

On Tue, 20 Nov 2018 16:47:19 +0100
Pavel Popa <pashinho1990@gmail.com> wrote:

> Well, here's the output from the `ip link` cmd:
>     3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>         link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
>         prog/xdp id 1 tag 1cd982ef22273bda jited
>     4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>         link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
>         prog/xdp id 1 tag 1cd982ef22273bda jited
> 
> As you can see, there's the XDP program ID 1 executing on them.
> However, there's definitely something interesting happening when
> bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
> program just returns XDP_PASS while the following line gets printed in
> kern.log:
>     eth3: bad gso: type: 164, size: 256
> 
> No idea what's wrong here.
> Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
> which my XDP program executes bpf_redirect_map(&dev_map,
> fib_params.ifindex, 0), the following gets printed in
>
> /sys/kernel/debug/tracing/trace_pipe:
>     xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
> to_ifindex=0 err=-14 map_id=0 map_index=4

The err=-14 is -EFAULT.

Notice "ifindex=3" but "to_ifindex=0", which is the problem.  The
"map_index=4" is correct, but "to_ifindex" does a lookup in the map for
the net_device->ifindex stored in this map.  It is fairly unlikely that
you added device with ifindex=0 to map index 4, I presume?

Then I was thinking, maybe the "map_index=4" doesn't contain anything,
but reading the code, that will return err=-22 (#define EINVAL 22),
which it not the case.

Assuming that map_index=4 does contain a valid net_device. Following
the code via __bpf_tx_xdp_map -> dev_map_enqueue, I simply cannot find
an -EFAULT err return value.

--Jesper


> I feel this last one to be somewhat related to the comment here
> https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
> Is it correct? If so, what does this precisely mean? Is there any way
> to get around with this? Because what I'm doing is simply using the
> BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
> packets between "XDP ports".
> 
> Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
> <dsahern@gmail.com> ha scritto:
> >
> > On 11/20/18 7:18 AM, Pavel Popa wrote:  
> > > Hi all,
> > >
> > > I've implemented a XDP forwarding program using the bpf_fib_lookup()
> > > helper, and loaded it in the kernel as XDP driver mode (i.e. executed
> > > at the virtio_net driver level). The only problem is that the
> > > receiving virtio network interface seems to drop the XDP packet after
> > > successfully executing my XDP program.
> > > Kernel: 4.18.10
> > >
> > > my_xdp_fwd_kern.c:
> > > /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
> > > rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> > > BPF_FIB_LOOKUP_DIRECT);
> > > /* made sure this returns 4 (i.e. XDP_REDIRECT) */
> > > rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
> > > return rc;
> > >
> > > I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
> > > is the correct dev index from FIB lookup.
> > > dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
> > > for (i = 1; i < 64; i++)
> > >     bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
> > >
> > > I'm passing the following to the qemu cmd line for the 2 devices I
> > > want to run XDP on (as stated here
> > > https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
> > > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > > \
> > > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > > \
> > >
> > > In the guest enabling also the MultiQueue feature, as stated here
> > > https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
> > > What I'm left with is debugging the virtio_net kernel module by adding
> > > a bunch of printk() and see what happens, especially here
> > > https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
> > >
> > > Am I doing something wrong here? What I'm missing?
> > >  
> >
> > I believe at this point you can drop the gso,tso,ufo and ecn args. I use
> > virtio for development and these days start my VMs with only:
> >
> > ...,mq=on,guest_csum=off,...
> >
> > After that are you installing the xdp program on all interfaces that can
> > be used for forwarding? ie., if it transmits a packet in XDP mode it
> > needs the xdp program loaded. For example I use:
> >
> > xdp_fwd eth1 eth2 eth3 eth4
> >
> >
> > From there:
> >
> > echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
> > cat /sys/kernel/debug/tracing/trace_pipe
> >  



-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

Re: qemu-kvm XDP forwarding with virtio_net

[David Ahern]

On 11/20/18 11:14 AM, Jesper Dangaard Brouer wrote:
> On Tue, 20 Nov 2018 16:47:19 +0100
> Pavel Popa <pashinho1990@gmail.com> wrote:
> 
>> Well, here's the output from the `ip link` cmd:
>>     3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>>         link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
>>         prog/xdp id 1 tag 1cd982ef22273bda jited
>>     4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>>         link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
>>         prog/xdp id 1 tag 1cd982ef22273bda jited
>>
>> As you can see, there's the XDP program ID 1 executing on them.
>> However, there's definitely something interesting happening when
>> bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
>> program just returns XDP_PASS while the following line gets printed in
>> kern.log:
>>     eth3: bad gso: type: 164, size: 256
>>
>> No idea what's wrong here.
>> Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
>> which my XDP program executes bpf_redirect_map(&dev_map,
>> fib_params.ifindex, 0), the following gets printed in
>>
>> /sys/kernel/debug/tracing/trace_pipe:
>>     xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
>> to_ifindex=0 err=-14 map_id=0 map_index=4
> 
> The err=-14 is -EFAULT.
> 
> Notice "ifindex=3" but "to_ifindex=0", which is the problem.  The
> "map_index=4" is correct, but "to_ifindex" does a lookup in the map for
> the net_device->ifindex stored in this map.  It is fairly unlikely that
> you added device with ifindex=0 to map index 4, I presume?
> 
> Then I was thinking, maybe the "map_index=4" doesn't contain anything,
> but reading the code, that will return err=-22 (#define EINVAL 22),
> which it not the case.
> 
> Assuming that map_index=4 does contain a valid net_device. Following
> the code via __bpf_tx_xdp_map -> dev_map_enqueue, I simply cannot find
> an -EFAULT err return value.
> 

Pavel:

Does the xdp_fwd sample work as is? you should be able to use it in your
setup with out changes to verify basic functionality.

From there you can check the fib lookup:
    perf record -e fib:* -a -- sleep 5
    <run traffic during 5-second window>
    perf script

Look at the FIB lookup result and egress device. Is it correct? The
fib_params.ifindex is set based on the egress device from the fib lookup.

Re: qemu-kvm XDP forwarding with virtio_net

[Pavel Popa]

After setting up the devmap I print its contents.
    dumping DEVMAP:
        k = 1, v = 1
        k = 2, v = 2
        k = 3, v = 3
        k = 4, v = 4
        k = 5, v = 4
        k = 6, v = 4
        ...
        k = 63, v = 4

> ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state
UP mode DEFAULT group default qlen 1000
    link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
    prog/xdp id 1 tag 1cd982ef22273bda jited
4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state
UP mode DEFAULT group default qlen 1000
    link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
    prog/xdp id 1 tag 1cd982ef22273bda jited

eth1: 172.17.102.143/23 (this is the management interface)
eth2: 192.168.1.101/24 (XDP "host-only" interface)
eth3: 192.168.0.101/24 (XDP "host-only" interface)

The XDP program is triggered by the reception of a packet on eth3
(ifindex 3), it does its thing and performs the routing lookup by
bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
BPF_FIB_LOOKUP_DIRECT) wich returns BPF_FIB_LKUP_RET_SUCCESS as the
packet's dst IP is 192.168.1.1. Thus, fib.params = 4 (I'm logging all
of this in /sys/kernel/debug/tracing/trace_pipe), i.e. forward over
ifindex 4 (eth2) which mapped value in devmap is 4. So I have no idea
what "to_ifindex=0" means here. I'm totally blocked on this.
Il giorno mar 20 nov 2018 alle ore 19:14 Jesper Dangaard Brouer
<brouer@redhat.com> ha scritto:
>
> On Tue, 20 Nov 2018 16:47:19 +0100
> Pavel Popa <pashinho1990@gmail.com> wrote:
>
> > Well, here's the output from the `ip link` cmd:
> >     3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
> >         link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
> >         prog/xdp id 1 tag 1cd982ef22273bda jited
> >     4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
> >         link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
> >         prog/xdp id 1 tag 1cd982ef22273bda jited
> >
> > As you can see, there's the XDP program ID 1 executing on them.
> > However, there's definitely something interesting happening when
> > bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
> > program just returns XDP_PASS while the following line gets printed in
> > kern.log:
> >     eth3: bad gso: type: 164, size: 256
> >
> > No idea what's wrong here.
> > Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
> > which my XDP program executes bpf_redirect_map(&dev_map,
> > fib_params.ifindex, 0), the following gets printed in
> >
> > /sys/kernel/debug/tracing/trace_pipe:
> >     xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
> > to_ifindex=0 err=-14 map_id=0 map_index=4
>
> The err=-14 is -EFAULT.
>
> Notice "ifindex=3" but "to_ifindex=0", which is the problem.  The
> "map_index=4" is correct, but "to_ifindex" does a lookup in the map for
> the net_device->ifindex stored in this map.  It is fairly unlikely that
> you added device with ifindex=0 to map index 4, I presume?
>
> Then I was thinking, maybe the "map_index=4" doesn't contain anything,
> but reading the code, that will return err=-22 (#define EINVAL 22),
> which it not the case.
>
> Assuming that map_index=4 does contain a valid net_device. Following
> the code via __bpf_tx_xdp_map -> dev_map_enqueue, I simply cannot find
> an -EFAULT err return value.
>
> --Jesper
>
>
> > I feel this last one to be somewhat related to the comment here
> > https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
> > Is it correct? If so, what does this precisely mean? Is there any way
> > to get around with this? Because what I'm doing is simply using the
> > BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
> > packets between "XDP ports".
> >
> > Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
> > <dsahern@gmail.com> ha scritto:
> > >
> > > On 11/20/18 7:18 AM, Pavel Popa wrote:
> > > > Hi all,
> > > >
> > > > I've implemented a XDP forwarding program using the bpf_fib_lookup()
> > > > helper, and loaded it in the kernel as XDP driver mode (i.e. executed
> > > > at the virtio_net driver level). The only problem is that the
> > > > receiving virtio network interface seems to drop the XDP packet after
> > > > successfully executing my XDP program.
> > > > Kernel: 4.18.10
> > > >
> > > > my_xdp_fwd_kern.c:
> > > > /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
> > > > rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> > > > BPF_FIB_LOOKUP_DIRECT);
> > > > /* made sure this returns 4 (i.e. XDP_REDIRECT) */
> > > > rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
> > > > return rc;
> > > >
> > > > I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
> > > > is the correct dev index from FIB lookup.
> > > > dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
> > > > for (i = 1; i < 64; i++)
> > > >     bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
> > > >
> > > > I'm passing the following to the qemu cmd line for the 2 devices I
> > > > want to run XDP on (as stated here
> > > > https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
> > > > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > > > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > > > \
> > > > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > > > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > > > \
> > > >
> > > > In the guest enabling also the MultiQueue feature, as stated here
> > > > https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
> > > > What I'm left with is debugging the virtio_net kernel module by adding
> > > > a bunch of printk() and see what happens, especially here
> > > > https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
> > > >
> > > > Am I doing something wrong here? What I'm missing?
> > > >
> > >
> > > I believe at this point you can drop the gso,tso,ufo and ecn args. I use
> > > virtio for development and these days start my VMs with only:
> > >
> > > ...,mq=on,guest_csum=off,...
> > >
> > > After that are you installing the xdp program on all interfaces that can
> > > be used for forwarding? ie., if it transmits a packet in XDP mode it
> > > needs the xdp program loaded. For example I use:
> > >
> > > xdp_fwd eth1 eth2 eth3 eth4
> > >
> > >
> > > From there:
> > >
> > > echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
> > > cat /sys/kernel/debug/tracing/trace_pipe
> > >
>
>
>
> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer

Re: qemu-kvm XDP forwarding with virtio_net

[Pavel Popa]

For what I see, the only way to return -EFAULT is in this case
https://elixir.bootlin.com/linux/v4.18.10/source/net/core/filter.c#L3259.
This may explain the "to_ifindex=0" thing, as 'fwd' is initialized
NULL. But I don't understand the meaning of the
"xdp_map_invalid(xdp_prog, map_owner)" condition. So, if that's really
the case, what can be inferred from this?
Il giorno mer 21 nov 2018 alle ore 10:08 Pavel Popa
<pashinho1990@gmail.com> ha scritto:
>
> After setting up the devmap I print its contents.
>     dumping DEVMAP:
>         k = 1, v = 1
>         k = 2, v = 2
>         k = 3, v = 3
>         k = 4, v = 4
>         k = 5, v = 4
>         k = 6, v = 4
>         ...
>         k = 63, v = 4
>
> > ip link
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
> mode DEFAULT group default qlen 1000
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
> 2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
> state UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
> 3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state
> UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
>     prog/xdp id 1 tag 1cd982ef22273bda jited
> 4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state
> UP mode DEFAULT group default qlen 1000
>     link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
>     prog/xdp id 1 tag 1cd982ef22273bda jited
>
> eth1: 172.17.102.143/23 (this is the management interface)
> eth2: 192.168.1.101/24 (XDP "host-only" interface)
> eth3: 192.168.0.101/24 (XDP "host-only" interface)
>
> The XDP program is triggered by the reception of a packet on eth3
> (ifindex 3), it does its thing and performs the routing lookup by
> bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> BPF_FIB_LOOKUP_DIRECT) wich returns BPF_FIB_LKUP_RET_SUCCESS as the
> packet's dst IP is 192.168.1.1. Thus, fib.params = 4 (I'm logging all
> of this in /sys/kernel/debug/tracing/trace_pipe), i.e. forward over
> ifindex 4 (eth2) which mapped value in devmap is 4. So I have no idea
> what "to_ifindex=0" means here. I'm totally blocked on this.
> Il giorno mar 20 nov 2018 alle ore 19:14 Jesper Dangaard Brouer
> <brouer@redhat.com> ha scritto:
> >
> > On Tue, 20 Nov 2018 16:47:19 +0100
> > Pavel Popa <pashinho1990@gmail.com> wrote:
> >
> > > Well, here's the output from the `ip link` cmd:
> > >     3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
> > >         link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
> > >         prog/xdp id 1 tag 1cd982ef22273bda jited
> > >     4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
> > >         link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
> > >         prog/xdp id 1 tag 1cd982ef22273bda jited
> > >
> > > As you can see, there's the XDP program ID 1 executing on them.
> > > However, there's definitely something interesting happening when
> > > bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
> > > program just returns XDP_PASS while the following line gets printed in
> > > kern.log:
> > >     eth3: bad gso: type: 164, size: 256
> > >
> > > No idea what's wrong here.
> > > Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
> > > which my XDP program executes bpf_redirect_map(&dev_map,
> > > fib_params.ifindex, 0), the following gets printed in
> > >
> > > /sys/kernel/debug/tracing/trace_pipe:
> > >     xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
> > > to_ifindex=0 err=-14 map_id=0 map_index=4
> >
> > The err=-14 is -EFAULT.
> >
> > Notice "ifindex=3" but "to_ifindex=0", which is the problem.  The
> > "map_index=4" is correct, but "to_ifindex" does a lookup in the map for
> > the net_device->ifindex stored in this map.  It is fairly unlikely that
> > you added device with ifindex=0 to map index 4, I presume?
> >
> > Then I was thinking, maybe the "map_index=4" doesn't contain anything,
> > but reading the code, that will return err=-22 (#define EINVAL 22),
> > which it not the case.
> >
> > Assuming that map_index=4 does contain a valid net_device. Following
> > the code via __bpf_tx_xdp_map -> dev_map_enqueue, I simply cannot find
> > an -EFAULT err return value.
> >
> > --Jesper
> >
> >
> > > I feel this last one to be somewhat related to the comment here
> > > https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
> > > Is it correct? If so, what does this precisely mean? Is there any way
> > > to get around with this? Because what I'm doing is simply using the
> > > BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
> > > packets between "XDP ports".
> > >
> > > Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
> > > <dsahern@gmail.com> ha scritto:
> > > >
> > > > On 11/20/18 7:18 AM, Pavel Popa wrote:
> > > > > Hi all,
> > > > >
> > > > > I've implemented a XDP forwarding program using the bpf_fib_lookup()
> > > > > helper, and loaded it in the kernel as XDP driver mode (i.e. executed
> > > > > at the virtio_net driver level). The only problem is that the
> > > > > receiving virtio network interface seems to drop the XDP packet after
> > > > > successfully executing my XDP program.
> > > > > Kernel: 4.18.10
> > > > >
> > > > > my_xdp_fwd_kern.c:
> > > > > /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
> > > > > rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> > > > > BPF_FIB_LOOKUP_DIRECT);
> > > > > /* made sure this returns 4 (i.e. XDP_REDIRECT) */
> > > > > rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
> > > > > return rc;
> > > > >
> > > > > I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
> > > > > is the correct dev index from FIB lookup.
> > > > > dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
> > > > > for (i = 1; i < 64; i++)
> > > > >     bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
> > > > >
> > > > > I'm passing the following to the qemu cmd line for the 2 devices I
> > > > > want to run XDP on (as stated here
> > > > > https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
> > > > > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > > > > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > > > > \
> > > > > -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> > > > > ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> > > > > \
> > > > >
> > > > > In the guest enabling also the MultiQueue feature, as stated here
> > > > > https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
> > > > > What I'm left with is debugging the virtio_net kernel module by adding
> > > > > a bunch of printk() and see what happens, especially here
> > > > > https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
> > > > >
> > > > > Am I doing something wrong here? What I'm missing?
> > > > >
> > > >
> > > > I believe at this point you can drop the gso,tso,ufo and ecn args. I use
> > > > virtio for development and these days start my VMs with only:
> > > >
> > > > ...,mq=on,guest_csum=off,...
> > > >
> > > > After that are you installing the xdp program on all interfaces that can
> > > > be used for forwarding? ie., if it transmits a packet in XDP mode it
> > > > needs the xdp program loaded. For example I use:
> > > >
> > > > xdp_fwd eth1 eth2 eth3 eth4
> > > >
> > > >
> > > > From there:
> > > >
> > > > echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
> > > > cat /sys/kernel/debug/tracing/trace_pipe
> > > >
> >
> >
> >
> > --
> > Best regards,
> >   Jesper Dangaard Brouer
> >   MSc.CS, Principal Kernel Engineer at Red Hat
> >   LinkedIn: http://www.linkedin.com/in/brouer

Re: qemu-kvm XDP forwarding with virtio_net

[Jesper Dangaard Brouer]

On Wed, 21 Nov 2018 11:01:45 +0100
Pavel Popa <pashinho1990@gmail.com> wrote:

> For what I see, the only way to return -EFAULT is in this case
> https://elixir.bootlin.com/linux/v4.18.10/source/net/core/filter.c#L3259.
> This may explain the "to_ifindex=0" thing, as 'fwd' is initialized
> NULL. But I don't understand the meaning of the
> "xdp_map_invalid(xdp_prog, map_owner)" condition. So, if that's really
> the case, what can be inferred from this?

Are you using BPF-tail calls?

Well that code got removed in kernel 4.19:

 Commit f6069b9aa993 ("bpf: fix redirect to map under tail calls")
 https://git.kernel.org/torvalds/c/f6069b9aa993

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

$ git describe --contains  f6069b9aa993
v4.19-rc1~86^2~6^2

Re: qemu-kvm XDP forwarding with virtio_net

[Pavel Popa]

Yes I'm using tail-calls, and yes that's definitely the problem I was
thinking about. Gotta upgrade to 4.19 then. Thanks a lot for the fast
replies.
Il giorno mer 21 nov 2018 alle ore 11:52 Jesper Dangaard Brouer
<brouer@redhat.com> ha scritto:
>
> On Wed, 21 Nov 2018 11:01:45 +0100
> Pavel Popa <pashinho1990@gmail.com> wrote:
>
> > For what I see, the only way to return -EFAULT is in this case
> > https://elixir.bootlin.com/linux/v4.18.10/source/net/core/filter.c#L3259.
> > This may explain the "to_ifindex=0" thing, as 'fwd' is initialized
> > NULL. But I don't understand the meaning of the
> > "xdp_map_invalid(xdp_prog, map_owner)" condition. So, if that's really
> > the case, what can be inferred from this?
>
> Are you using BPF-tail calls?
>
> Well that code got removed in kernel 4.19:
>
>  Commit f6069b9aa993 ("bpf: fix redirect to map under tail calls")
>  https://git.kernel.org/torvalds/c/f6069b9aa993
>
> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer
>
> $ git describe --contains  f6069b9aa993
> v4.19-rc1~86^2~6^2

Re: qemu-kvm XDP forwarding with virtio_net

[Jason Wang]

[-- Attachment #1: Type: text/plain, Size: 5281 bytes --]


On 2018/11/21 上午2:14, Jesper Dangaard Brouer wrote:
> On Tue, 20 Nov 2018 16:47:19 +0100
> Pavel Popa <pashinho1990@gmail.com> wrote:
>
>> Well, here's the output from the `ip link` cmd:
>>      3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>>          link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
>>          prog/xdp id 1 tag 1cd982ef22273bda jited
>>      4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>>          link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
>>          prog/xdp id 1 tag 1cd982ef22273bda jited
>>
>> As you can see, there's the XDP program ID 1 executing on them.
>> However, there's definitely something interesting happening when
>> bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
>> program just returns XDP_PASS while the following line gets printed in
>> kern.log:
>>      eth3: bad gso: type: 164, size: 256


Looks like a bug in virtio-net driver since all gso should be disabled 
on host.

Could you please try the attached patch to see if it fixes the issue?


>>
>> No idea what's wrong here.
>> Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
>> which my XDP program executes bpf_redirect_map(&dev_map,
>> fib_params.ifindex, 0), the following gets printed in
>>
>> /sys/kernel/debug/tracing/trace_pipe:
>>      xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
>> to_ifindex=0 err=-14 map_id=0 map_index=4
> The err=-14 is -EFAULT.
>
> Notice "ifindex=3" but "to_ifindex=0", which is the problem.  The
> "map_index=4" is correct, but "to_ifindex" does a lookup in the map for
> the net_device->ifindex stored in this map.  It is fairly unlikely that
> you added device with ifindex=0 to map index 4, I presume?
>
> Then I was thinking, maybe the "map_index=4" doesn't contain anything,
> but reading the code, that will return err=-22 (#define EINVAL 22),
> which it not the case.
>
> Assuming that map_index=4 does contain a valid net_device. Following
> the code via __bpf_tx_xdp_map -> dev_map_enqueue, I simply cannot find
> an -EFAULT err return value.
>
> --Jesper
>
>
>> I feel this last one to be somewhat related to the comment here
>> https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
>> Is it correct? If so, what does this precisely mean? Is there any way
>> to get around with this? Because what I'm doing is simply using the
>> BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
>> packets between "XDP ports".
>>
>> Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
>> <dsahern@gmail.com> ha scritto:
>>> On 11/20/18 7:18 AM, Pavel Popa wrote:
>>>> Hi all,
>>>>
>>>> I've implemented a XDP forwarding program using the bpf_fib_lookup()
>>>> helper, and loaded it in the kernel as XDP driver mode (i.e. executed
>>>> at the virtio_net driver level). The only problem is that the
>>>> receiving virtio network interface seems to drop the XDP packet after
>>>> successfully executing my XDP program.
>>>> Kernel: 4.18.10
>>>>
>>>> my_xdp_fwd_kern.c:
>>>> /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
>>>> rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
>>>> BPF_FIB_LOOKUP_DIRECT);
>>>> /* made sure this returns 4 (i.e. XDP_REDIRECT) */
>>>> rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
>>>> return rc;
>>>>
>>>> I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
>>>> is the correct dev index from FIB lookup.
>>>> dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
>>>> for (i = 1; i < 64; i++)
>>>>      bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
>>>>
>>>> I'm passing the following to the qemu cmd line for the 2 devices I
>>>> want to run XDP on (as stated here
>>>> https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
>>>> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
>>>> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
>>>> \
>>>> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
>>>> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
>>>> \
>>>>
>>>> In the guest enabling also the MultiQueue feature, as stated here
>>>> https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
>>>> What I'm left with is debugging the virtio_net kernel module by adding
>>>> a bunch of printk() and see what happens, especially here
>>>> https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
>>>>
>>>> Am I doing something wrong here? What I'm missing?
>>>>   
>>> I believe at this point you can drop the gso,tso,ufo and ecn args. I use
>>> virtio for development and these days start my VMs with only:
>>>
>>> ...,mq=on,guest_csum=off,...


This looks like another bug that guest_cusm was not disabled 
automatically. Let me post a fix for this.

Thanks.


>>>
>>> After that are you installing the xdp program on all interfaces that can
>>> be used for forwarding? ie., if it transmits a packet in XDP mode it
>>> needs the xdp program loaded. For example I use:
>>>
>>> xdp_fwd eth1 eth2 eth3 eth4
>>>
>>>
>>>  From there:
>>>
>>> echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
>>> cat /sys/kernel/debug/tracing/trace_pipe
>>>   
>
>

[-- Attachment #2: 0001-virtio-net-keep-vnet-header-zeroed-after-processing-.patch --]
[-- Type: text/x-patch, Size: 2218 bytes --]

From 7cc197b6f932fe74953ffa1ca1af9d2d5c15dd56 Mon Sep 17 00:00:00 2001
From: Jason Wang <jasowang@redhat.com>
Date: Thu, 22 Nov 2018 10:14:38 +0800
Subject: [PATCH] virtio-net: keep vnet header zeroed after processing XDP

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/net/virtio_net.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 3e2c041d76ac..7f9ccd436b83 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -364,7 +364,8 @@ static unsigned int mergeable_ctx_to_truesize(void *mrg_ctx)
 static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 				   struct receive_queue *rq,
 				   struct page *page, unsigned int offset,
-				   unsigned int len, unsigned int truesize)
+				   unsigned int len, unsigned int truesize,
+				   bool hdr_valid)
 {
 	struct sk_buff *skb;
 	struct virtio_net_hdr_mrg_rxbuf *hdr;
@@ -386,7 +387,8 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	else
 		hdr_padded_len = sizeof(struct padded_vnet_hdr);
 
-	memcpy(hdr, p, hdr_len);
+	if (hdr_valid)
+		memcpy(hdr, p, hdr_len);
 
 	len -= hdr_len;
 	offset += hdr_padded_len;
@@ -738,7 +740,8 @@ static struct sk_buff *receive_big(struct net_device *dev,
 				   struct virtnet_rq_stats *stats)
 {
 	struct page *page = buf;
-	struct sk_buff *skb = page_to_skb(vi, rq, page, 0, len, PAGE_SIZE);
+	struct sk_buff *skb = page_to_skb(vi, rq, page, 0, len,
+					  PAGE_SIZE, true);
 
 	stats->bytes += len - vi->hdr_len;
 	if (unlikely(!skb))
@@ -841,7 +844,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 				rcu_read_unlock();
 				put_page(page);
 				head_skb = page_to_skb(vi, rq, xdp_page,
-						       offset, len, PAGE_SIZE);
+						       offset, len,
+						       PAGE_SIZE, false);
 				return head_skb;
 			}
 			break;
@@ -897,7 +901,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		goto err_skb;
 	}
 
-	head_skb = page_to_skb(vi, rq, page, offset, len, truesize);
+	head_skb = page_to_skb(vi, rq, page, offset, len, truesize,
+			       xdp_prog != NULL);
 	curr_skb = head_skb;
 
 	if (unlikely(!curr_skb))
-- 
2.17.1

Re: qemu-kvm XDP forwarding with virtio_net

[Pavel Popa]

Hi Jason,

I confirm that the patch you sent me, together with "[PATCH net 1/2]
virtio-net: disable guest csum during XDP set" and "[PATCH net 2/2]
virtio-net: fail XDP set if guest csum is negotiated", have fixed the
"bad gso" issue.

Cheers
Il giorno gio 22 nov 2018 alle ore 03:15 Jason Wang
<jasowang@redhat.com> ha scritto:
>
>
> On 2018/11/21 上午2:14, Jesper Dangaard Brouer wrote:
> > On Tue, 20 Nov 2018 16:47:19 +0100
> > Pavel Popa <pashinho1990@gmail.com> wrote:
> >
> >> Well, here's the output from the `ip link` cmd:
> >>      3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
> >>          link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
> >>          prog/xdp id 1 tag 1cd982ef22273bda jited
> >>      4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
> >>          link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
> >>          prog/xdp id 1 tag 1cd982ef22273bda jited
> >>
> >> As you can see, there's the XDP program ID 1 executing on them.
> >> However, there's definitely something interesting happening when
> >> bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
> >> program just returns XDP_PASS while the following line gets printed in
> >> kern.log:
> >>      eth3: bad gso: type: 164, size: 256
>
>
> Looks like a bug in virtio-net driver since all gso should be disabled
> on host.
>
> Could you please try the attached patch to see if it fixes the issue?
>
>
> >>
> >> No idea what's wrong here.
> >> Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
> >> which my XDP program executes bpf_redirect_map(&dev_map,
> >> fib_params.ifindex, 0), the following gets printed in
> >>
> >> /sys/kernel/debug/tracing/trace_pipe:
> >>      xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
> >> to_ifindex=0 err=-14 map_id=0 map_index=4
> > The err=-14 is -EFAULT.
> >
> > Notice "ifindex=3" but "to_ifindex=0", which is the problem.  The
> > "map_index=4" is correct, but "to_ifindex" does a lookup in the map for
> > the net_device->ifindex stored in this map.  It is fairly unlikely that
> > you added device with ifindex=0 to map index 4, I presume?
> >
> > Then I was thinking, maybe the "map_index=4" doesn't contain anything,
> > but reading the code, that will return err=-22 (#define EINVAL 22),
> > which it not the case.
> >
> > Assuming that map_index=4 does contain a valid net_device. Following
> > the code via __bpf_tx_xdp_map -> dev_map_enqueue, I simply cannot find
> > an -EFAULT err return value.
> >
> > --Jesper
> >
> >
> >> I feel this last one to be somewhat related to the comment here
> >> https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
> >> Is it correct? If so, what does this precisely mean? Is there any way
> >> to get around with this? Because what I'm doing is simply using the
> >> BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
> >> packets between "XDP ports".
> >>
> >> Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
> >> <dsahern@gmail.com> ha scritto:
> >>> On 11/20/18 7:18 AM, Pavel Popa wrote:
> >>>> Hi all,
> >>>>
> >>>> I've implemented a XDP forwarding program using the bpf_fib_lookup()
> >>>> helper, and loaded it in the kernel as XDP driver mode (i.e. executed
> >>>> at the virtio_net driver level). The only problem is that the
> >>>> receiving virtio network interface seems to drop the XDP packet after
> >>>> successfully executing my XDP program.
> >>>> Kernel: 4.18.10
> >>>>
> >>>> my_xdp_fwd_kern.c:
> >>>> /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
> >>>> rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
> >>>> BPF_FIB_LOOKUP_DIRECT);
> >>>> /* made sure this returns 4 (i.e. XDP_REDIRECT) */
> >>>> rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
> >>>> return rc;
> >>>>
> >>>> I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
> >>>> is the correct dev index from FIB lookup.
> >>>> dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
> >>>> for (i = 1; i < 64; i++)
> >>>>      bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
> >>>>
> >>>> I'm passing the following to the qemu cmd line for the 2 devices I
> >>>> want to run XDP on (as stated here
> >>>> https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
> >>>> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> >>>> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> >>>> \
> >>>> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
> >>>> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
> >>>> \
> >>>>
> >>>> In the guest enabling also the MultiQueue feature, as stated here
> >>>> https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
> >>>> What I'm left with is debugging the virtio_net kernel module by adding
> >>>> a bunch of printk() and see what happens, especially here
> >>>> https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
> >>>>
> >>>> Am I doing something wrong here? What I'm missing?
> >>>>
> >>> I believe at this point you can drop the gso,tso,ufo and ecn args. I use
> >>> virtio for development and these days start my VMs with only:
> >>>
> >>> ...,mq=on,guest_csum=off,...
>
>
> This looks like another bug that guest_cusm was not disabled
> automatically. Let me post a fix for this.
>
> Thanks.
>
>
> >>>
> >>> After that are you installing the xdp program on all interfaces that can
> >>> be used for forwarding? ie., if it transmits a packet in XDP mode it
> >>> needs the xdp program loaded. For example I use:
> >>>
> >>> xdp_fwd eth1 eth2 eth3 eth4
> >>>
> >>>
> >>>  From there:
> >>>
> >>> echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
> >>> cat /sys/kernel/debug/tracing/trace_pipe
> >>>
> >
> >

Re: qemu-kvm XDP forwarding with virtio_net

[Jason Wang]

On 2018/11/24 上午1:09, Pavel Popa wrote:
> Hi Jason,
>
> I confirm that the patch you sent me, together with "[PATCH net 1/2]
> virtio-net: disable guest csum during XDP set" and "[PATCH net 2/2]
> virtio-net: fail XDP set if guest csum is negotiated", have fixed the
> "bad gso" issue.
>
> Cheers


Thanks for the testing.

Let me post a formal patch.


> Il giorno gio 22 nov 2018 alle ore 03:15 Jason Wang
> <jasowang@redhat.com> ha scritto:
>>
>> On 2018/11/21 上午2:14, Jesper Dangaard Brouer wrote:
>>> On Tue, 20 Nov 2018 16:47:19 +0100
>>> Pavel Popa <pashinho1990@gmail.com> wrote:
>>>
>>>> Well, here's the output from the `ip link` cmd:
>>>>       3: eth3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>>>>           link/ether 52:54:fc:47:e2:d3 brd ff:ff:ff:ff:ff:ff
>>>>           prog/xdp id 1 tag 1cd982ef22273bda jited
>>>>       4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc mq state UP
>>>>           link/ether 52:54:55:d3:50:ee brd ff:ff:ff:ff:ff:ff
>>>>           prog/xdp id 1 tag 1cd982ef22273bda jited
>>>>
>>>> As you can see, there's the XDP program ID 1 executing on them.
>>>> However, there's definitely something interesting happening when
>>>> bpf_fib_lookup() returns BPF_FIB_LKUP_RET_NO_NEIGH, for which my XDP
>>>> program just returns XDP_PASS while the following line gets printed in
>>>> kern.log:
>>>>       eth3: bad gso: type: 164, size: 256
>>
>> Looks like a bug in virtio-net driver since all gso should be disabled
>> on host.
>>
>> Could you please try the attached patch to see if it fixes the issue?
>>
>>
>>>> No idea what's wrong here.
>>>> Also, when bpf_fib_lookup() returns BPF_FIB_LKUP_RET_SUCCESS, for
>>>> which my XDP program executes bpf_redirect_map(&dev_map,
>>>> fib_params.ifindex, 0), the following gets printed in
>>>>
>>>> /sys/kernel/debug/tracing/trace_pipe:
>>>>       xdp_redirect_map_err: prog_id=1 action=REDIRECT ifindex=3
>>>> to_ifindex=0 err=-14 map_id=0 map_index=4
>>> The err=-14 is -EFAULT.
>>>
>>> Notice "ifindex=3" but "to_ifindex=0", which is the problem.  The
>>> "map_index=4" is correct, but "to_ifindex" does a lookup in the map for
>>> the net_device->ifindex stored in this map.  It is fairly unlikely that
>>> you added device with ifindex=0 to map index 4, I presume?
>>>
>>> Then I was thinking, maybe the "map_index=4" doesn't contain anything,
>>> but reading the code, that will return err=-22 (#define EINVAL 22),
>>> which it not the case.
>>>
>>> Assuming that map_index=4 does contain a valid net_device. Following
>>> the code via __bpf_tx_xdp_map -> dev_map_enqueue, I simply cannot find
>>> an -EFAULT err return value.
>>>
>>> --Jesper
>>>
>>>
>>>> I feel this last one to be somewhat related to the comment here
>>>> https://elixir.bootlin.com/linux/v4.18.10/source/samples/bpf/xdp_fwd_kern.c#L107.
>>>> Is it correct? If so, what does this precisely mean? Is there any way
>>>> to get around with this? Because what I'm doing is simply using the
>>>> BPF_MAP_TYPE_DEVMAP with the bpf_redirect_map() helper to forward
>>>> packets between "XDP ports".
>>>>
>>>> Il giorno mar 20 nov 2018 alle ore 15:39 David Ahern
>>>> <dsahern@gmail.com> ha scritto:
>>>>> On 11/20/18 7:18 AM, Pavel Popa wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> I've implemented a XDP forwarding program using the bpf_fib_lookup()
>>>>>> helper, and loaded it in the kernel as XDP driver mode (i.e. executed
>>>>>> at the virtio_net driver level). The only problem is that the
>>>>>> receiving virtio network interface seems to drop the XDP packet after
>>>>>> successfully executing my XDP program.
>>>>>> Kernel: 4.18.10
>>>>>>
>>>>>> my_xdp_fwd_kern.c:
>>>>>> /* made sure this returns 0 (i.e. BPF_FIB_LKUP_RET_SUCCESS) */
>>>>>> rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params),
>>>>>> BPF_FIB_LOOKUP_DIRECT);
>>>>>> /* made sure this returns 4 (i.e. XDP_REDIRECT) */
>>>>>> rc = bpf_redirect_map(&dev_map, fib_params.ifindex, 0);
>>>>>> return rc;
>>>>>>
>>>>>> I checked that rc is indeed XDP_REDIRECT and that fib_params.ifindex
>>>>>> is the correct dev index from FIB lookup.
>>>>>> dev_map is setup by the userspace my_xdp_fwd_user.c component as follows:
>>>>>> for (i = 1; i < 64; i++)
>>>>>>       bpf_map_update_elem(devmap_fd, &i, &i, BPF_ANY);
>>>>>>
>>>>>> I'm passing the following to the qemu cmd line for the 2 devices I
>>>>>> want to run XDP on (as stated here
>>>>>> https://marc.info/?l=xdp-newbies&m=149486931113651&w=2):
>>>>>> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
>>>>>> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
>>>>>> \
>>>>>> -device virtio-net-pci,mq=on,vectors=18,rx_queue_size=1024,tx_queue_size=512,
>>>>>> ... ,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off
>>>>>> \
>>>>>>
>>>>>> In the guest enabling also the MultiQueue feature, as stated here
>>>>>> https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature.
>>>>>> What I'm left with is debugging the virtio_net kernel module by adding
>>>>>> a bunch of printk() and see what happens, especially here
>>>>>> https://elixir.bootlin.com/linux/v4.18.10/source/drivers/net/virtio_net.c#L667.
>>>>>>
>>>>>> Am I doing something wrong here? What I'm missing?
>>>>>>
>>>>> I believe at this point you can drop the gso,tso,ufo and ecn args. I use
>>>>> virtio for development and these days start my VMs with only:
>>>>>
>>>>> ...,mq=on,guest_csum=off,...
>>
>> This looks like another bug that guest_cusm was not disabled
>> automatically. Let me post a fix for this.
>>
>> Thanks.
>>
>>
>>>>> After that are you installing the xdp program on all interfaces that can
>>>>> be used for forwarding? ie., if it transmits a packet in XDP mode it
>>>>> needs the xdp program loaded. For example I use:
>>>>>
>>>>> xdp_fwd eth1 eth2 eth3 eth4
>>>>>
>>>>>
>>>>>   From there:
>>>>>
>>>>> echo 1 > /sys/kernel/debug/tracing/events/xdp/enable
>>>>> cat /sys/kernel/debug/tracing/trace_pipe
>>>>>
>>>

Re: qemu-kvm XDP forwarding with virtio_net

[Jason Wang]

On 2018/11/26 下午2:36, Jason Wang wrote:
>
> On 2018/11/24 上午1:09, Pavel Popa wrote:
>> Hi Jason,
>>
>> I confirm that the patch you sent me, together with "[PATCH net 1/2]
>> virtio-net: disable guest csum during XDP set" and "[PATCH net 2/2]
>> virtio-net: fail XDP set if guest csum is negotiated", have fixed the
>> "bad gso" issue.
>>
>> Cheers
>
>
> Thanks for the testing.
>
> Let me post a formal patch.


Actually, there's a typo in the patch I attached.

The check xdp_prog != NULL should be !xdp_prog.

I will fix this and post soon.

Thanks