Tunneling fixes

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

Fixes bf5a755f ("net-gre-gro: Add GRE support to the GRO stack")

Signed-off-by Jesse Gross <[email protected]>

---
v2: No change.

---
 include/linux/netdevice.h |  4 ++--
 net/core/dev.c            |  2 +-
 net/ipv4/af_inet.c        | 15 ++++++++++++++-
 net/ipv4/gre_offload.c    |  5 +++++
 net/ipv4/udp_offload.c    |  6 +++---
 net/ipv6/ip6_offload.c    | 15 ++++++++++++++-
 6 files changed, 39 insertions(+), 8 deletions(-)

include/linux/netdevice.h +2 -2

index be693b3..f9eebd5 100644
@@ -2096,8 +2096,8 @@ struct napi_gro_cb {
        /* This is non-zero if the packet may be of the same flow. */
        u8      same_flow:1;
 
-       /* Used in udp_gro_receive */
-       u8      udp_mark:1;
+       /* Used in tunnel GRO receive */
+       u8      encap_mark:1;
 
        /* GRO checksum is valid */
        u8      csum_valid:1;

net/core/dev.c +1 -1

index edb7179..43c74ca 100644
@@ -4438,7 +4438,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
                NAPI_GRO_CB(skb)->same_flow = 0;
                NAPI_GRO_CB(skb)->flush = 0;
                NAPI_GRO_CB(skb)->free = 0;
-               NAPI_GRO_CB(skb)->udp_mark = 0;
+               NAPI_GRO_CB(skb)->encap_mark = 0;
                NAPI_GRO_CB(skb)->gro_remcsum_start = 0;
 
                /* Setup for GRO checksum validation */

net/ipv4/af_inet.c +14 -1

index 9659233..0fefba6 100644
@@ -1380,6 +1380,19 @@ out:
        return pp;
 }
 
+static struct sk_buff **ipip_gro_receive(struct sk_buff **head,
+                                        struct sk_buff *skb)
+{
+       if (NAPI_GRO_CB(skb)->encap_mark) {
+               NAPI_GRO_CB(skb)->flush = 1;
+               return NULL;
+       }
+
+       NAPI_GRO_CB(skb)->encap_mark = 1;
+
+       return inet_gro_receive(head, skb);
+}
+
 #define SECONDS_PER_DAY        86400
 
 /* inet_current_timestamp - Return IP network timestamp

@@ -1682,7 +1695,7 @@ static struct packet_offload ip_packet_offload __read_mostly = {
 static const struct net_offload ipip_offload = {
        .callbacks = {
                .gso_segment    = inet_gso_segment,
-               .gro_receive    = inet_gro_receive,
+               .gro_receive    = ipip_gro_receive,
                .gro_complete   = ipip_gro_complete,
        },
 };

net/ipv4/gre_offload.c +5 -0

index 540866d..dd03161 100644
@@ -126,6 +126,11 @@ static struct sk_buff **gre_gro_receive(struct sk_buff **head,
        struct packet_offload *ptype;
        __be16 type;
 
+       if (NAPI_GRO_CB(skb)->encap_mark)
+               goto out;
+
+       NAPI_GRO_CB(skb)->encap_mark = 1;
+
        off = skb_gro_offset(skb);
        hlen = off + sizeof(*greh);
        greh = skb_gro_header_fast(skb, off);

net/ipv4/udp_offload.c +3 -3

index 8a3405a..8007f73 100644
@@ -311,14 +311,14 @@ struct sk_buff **udp_gro_receive(struct sk_buff **head, struct sk_buff *skb,
        unsigned int off = skb_gro_offset(skb);
        int flush = 1;
 
-       if (NAPI_GRO_CB(skb)->udp_mark ||
+       if (NAPI_GRO_CB(skb)->encap_mark ||
            (skb->ip_summed != CHECKSUM_PARTIAL &&
             NAPI_GRO_CB(skb)->csum_cnt == 0 &&
             !NAPI_GRO_CB(skb)->csum_valid))
                goto out;
 
-       /* mark that this skb passed once through the udp gro layer */
-       NAPI_GRO_CB(skb)->udp_mark = 1;
+       /* mark that this skb passed once through the tunnel gro layer */
+       NAPI_GRO_CB(skb)->encap_mark = 1;
 
        rcu_read_lock();
        uo_priv = rcu_dereference(udp_offload_base);

net/ipv6/ip6_offload.c +14 -2

index eeca943..82e9f30 100644
@@ -258,6 +258,19 @@ out:
        return pp;
 }
 
+static struct sk_buff **sit_gro_receive(struct sk_buff **head,
+                                       struct sk_buff *skb)
+{
+       if (NAPI_GRO_CB(skb)->encap_mark) {
+               NAPI_GRO_CB(skb)->flush = 1;
+               return NULL;
+       }
+
+       NAPI_GRO_CB(skb)->encap_mark = 1;
+
+       return ipv6_gro_receive(head, skb);
+}
+
 static int ipv6_gro_complete(struct sk_buff *skb, int nhoff)
 {
        const struct net_offload *ops;

@@ -302,7 +315,7 @@ static struct packet_offload ipv6_packet_offload __read_mostly = {
 static const struct net_offload sit_offload = {
        .callbacks = {
                .gso_segment    = ipv6_gso_segment,
-               .gro_receive    = ipv6_gro_receive,
+               .gro_receive    = sit_gro_receive,
                .gro_complete   = sit_gro_complete,
        },
 };
--

2.5.0

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

Quoted 42 lines · Tom Herbert

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Quoted 5 lines

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Jesse does have a point. Drivers aren't checking for this kind of thing currently as the transmit side doesn't generate these kind of frames. The fact that GRO is makes things a bit more messy as we will really need to restructure the GSO code in order to handle it. As far as drivers testing for it I am pretty certain the i40e isn't. I would wonder if we need to add yet another GSO bit to indicate that we support multiple layers of encapsulation. I'm pretty sure the only way we could possibly handle it would be in software since what you are indicating is a indeterminate number of headers that all require updates.

Quoted 8 lines

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

Quoted 7 lines

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

The segmentation code isn't designed to handle more than 2 layers of headers. Currently we have the pointers for the inner headers and the outer headers. If you are talking about adding yet another level we would need additional pointers in the skbuff to handle them and we currently don't have them at present.

Quoted 6 lines

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 10 lines

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

This isn't about if drivers can handle it. It is about if the skbuff can handle it. The problem as it stands right now is that we start losing data once we go past 1 level of encapsulation. We only have the standard mac_header, network_header, transport_header, and then the inner set of the same pointers. If we try to go multiple levels deep we start losing data.

If we are wanting to start allowing unlimited headers then maybe we need to start allowing for "partial" GRO to complement the partial GSO implementation I have. With that at least we might be able to track the first and last headers and we could leave the remaining headers static. Then when the frame made it to the driver it would know that the headers in the long list can be replicated and it only has to update the outer network header and the inner transport header, otherwise if it doesn't support that it can just chop up the frame in software and send that out.

- Alex

Quoted 99 lines · Alexander Duyck

Quoted 42 lines · Tom Herbert

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Quoted 5 lines

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Jesse does have a point. Drivers aren't checking for this kind of thing currently as the transmit side doesn't generate these kind of frames. The fact that GRO is makes things a bit more messy as we will really need to restructure the GSO code in order to handle it. As far as drivers testing for it I am pretty certain the i40e isn't. I would wonder if we need to add yet another GSO bit to indicate that we support multiple layers of encapsulation. I'm pretty sure the only way we could possibly handle it would be in software since what you are indicating is a indeterminate number of headers that all require updates.

Quoted 8 lines

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

Quoted 7 lines

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

The segmentation code isn't designed to handle more than 2 layers of headers. Currently we have the pointers for the inner headers and the outer headers. If you are talking about adding yet another level we would need additional pointers in the skbuff to handle them and we currently don't have them at present.

Quoted 6 lines

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 10 lines

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

Quoted 7 lines

This isn't about if drivers can handle it. It is about if the skbuff can handle it. The problem as it stands right now is that we start losing data once we go past 1 level of encapsulation. We only have the standard mac_header, network_header, transport_header, and then the inner set of the same pointers. If we try to go multiple levels deep we start losing data.

Huh? GUE/FOU has been running perfectly well with two levels of encapsulation for over a year now. We never had to add anything to skbuff to make that work. If "losing data" is a problem please provide the *reproducible* test case for that and we'll debug that.

Quoted 108 lines · Tom Herbert

Quoted 99 lines · Alexander Duyck

Quoted 42 lines · Tom Herbert

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Quoted 5 lines

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Jesse does have a point. Drivers aren't checking for this kind of thing currently as the transmit side doesn't generate these kind of frames. The fact that GRO is makes things a bit more messy as we will really need to restructure the GSO code in order to handle it. As far as drivers testing for it I am pretty certain the i40e isn't. I would wonder if we need to add yet another GSO bit to indicate that we support multiple layers of encapsulation. I'm pretty sure the only way we could possibly handle it would be in software since what you are indicating is a indeterminate number of headers that all require updates.

Quoted 8 lines

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

Quoted 7 lines

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

The segmentation code isn't designed to handle more than 2 layers of headers. Currently we have the pointers for the inner headers and the outer headers. If you are talking about adding yet another level we would need additional pointers in the skbuff to handle them and we currently don't have them at present.

Quoted 6 lines

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 10 lines

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

Quoted 7 lines

This isn't about if drivers can handle it. It is about if the skbuff can handle it. The problem as it stands right now is that we start losing data once we go past 1 level of encapsulation. We only have the standard mac_header, network_header, transport_header, and then the inner set of the same pointers. If we try to go multiple levels deep we start losing data.

Quoted 4 lines

Huh? GUE/FOU has been running perfectly well with two levels of encapsulation for over a year now. We never had to add anything to skbuff to make that work. If "losing data" is a problem please provide the *reproducible* test case for that and we'll debug that.

I'm guessing most of your examples involve either a remote checksum being enabled or using NICs that don't support any tunnel offloads? Hardware needs to be able to identify where headers are in order to perform most of their offloads for TSO. We either have to parse to find them or we are provided with them by the stack. GSO can work around it as long as we don't stack checksum based offload with non-checksum of the same type.

mostIf for example you were to try and send a frame that had either an inner or outer GRE tunnel in addition to a UDP tunnel most NICs would probably screw it up.

Up until now that hasn't been an issue. As we
start turning on offload support for multiple tunnel types thanks to the partial offloads it will come back and bite us if we try to tell hardware to handle more than 2 levels of headers. I'm thinking if nothing else we might have to add yet another bit to GSO for stacked tunnels which can probably only be supported via partial GSO and only if we can get away with just replicating headers.

It looks like we need to go through and probably clean up both the GSO and GRO code. First we have to get the GSO code setup so that it can fully handle multiple levels of tunnels. The code as it is now assumes you would only have one level and we are configuring the headers as such. In addition the GRO code doesn't seem to place the header offsets correctly. For instance, from what I can tell it looks like the inner transport offset is never updated. We will probably need to have pointers for the inner-most and outer-most set of headers and from there we can start handling the offloads.

- Alex

Quoted 122 lines · Alexander Duyck

Quoted 108 lines · Tom Herbert

Quoted 99 lines · Alexander Duyck

Quoted 42 lines · Tom Herbert

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Quoted 5 lines

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Jesse does have a point. Drivers aren't checking for this kind of thing currently as the transmit side doesn't generate these kind of frames. The fact that GRO is makes things a bit more messy as we will really need to restructure the GSO code in order to handle it. As far as drivers testing for it I am pretty certain the i40e isn't. I would wonder if we need to add yet another GSO bit to indicate that we support multiple layers of encapsulation. I'm pretty sure the only way we could possibly handle it would be in software since what you are indicating is a indeterminate number of headers that all require updates.

Quoted 8 lines

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

Quoted 7 lines

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

The segmentation code isn't designed to handle more than 2 layers of headers. Currently we have the pointers for the inner headers and the outer headers. If you are talking about adding yet another level we would need additional pointers in the skbuff to handle them and we currently don't have them at present.

Quoted 6 lines

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 10 lines

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

Quoted 7 lines

This isn't about if drivers can handle it. It is about if the skbuff can handle it. The problem as it stands right now is that we start losing data once we go past 1 level of encapsulation. We only have the standard mac_header, network_header, transport_header, and then the inner set of the same pointers. If we try to go multiple levels deep we start losing data.

Quoted 4 lines

Huh? GUE/FOU has been running perfectly well with two levels of encapsulation for over a year now. We never had to add anything to skbuff to make that work. If "losing data" is a problem please provide the *reproducible* test case for that and we'll debug that.

I'm guessing most of your examples involve either a remote checksum being enabled or using NICs that don't support any tunnel offloads? Hardware needs to be able to identify where headers are in order to perform most of their offloads for TSO. We either have to parse to find them or we are provided with them by the stack. GSO can work around it as long as we don't stack checksum based offload with non-checksum of the same type.

Quoted 3 lines

mostIf for example you were to try and send a frame that had either an inner or outer GRE tunnel in addition to a UDP tunnel most NICs would probably screw it up.

Please be more precise. Obviously we're only talking about the few NICs that even support UDP tunnel offload so it's not most NICs. Also, there is a big difference between "probably" and "definitely"; no one has provided a single data point that that there is even an issue. For instance, looking a i40e I suspect this will work with GRE/UDP since the driver already deals with offsets and shouldn't care about intermediate levels of encapsulation.

Quoted 128 lines · Tom Herbert

Quoted 122 lines · Alexander Duyck

Quoted 108 lines · Tom Herbert

Quoted 99 lines · Alexander Duyck

Quoted 42 lines · Tom Herbert

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Quoted 5 lines

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Jesse does have a point. Drivers aren't checking for this kind of thing currently as the transmit side doesn't generate these kind of frames. The fact that GRO is makes things a bit more messy as we will really need to restructure the GSO code in order to handle it. As far as drivers testing for it I am pretty certain the i40e isn't. I would wonder if we need to add yet another GSO bit to indicate that we support multiple layers of encapsulation. I'm pretty sure the only way we could possibly handle it would be in software since what you are indicating is a indeterminate number of headers that all require updates.

Quoted 8 lines

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

Quoted 7 lines

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

The segmentation code isn't designed to handle more than 2 layers of headers. Currently we have the pointers for the inner headers and the outer headers. If you are talking about adding yet another level we would need additional pointers in the skbuff to handle them and we currently don't have them at present.

Quoted 6 lines

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 10 lines

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

Quoted 7 lines

This isn't about if drivers can handle it. It is about if the skbuff can handle it. The problem as it stands right now is that we start losing data once we go past 1 level of encapsulation. We only have the standard mac_header, network_header, transport_header, and then the inner set of the same pointers. If we try to go multiple levels deep we start losing data.

Quoted 4 lines

Huh? GUE/FOU has been running perfectly well with two levels of encapsulation for over a year now. We never had to add anything to skbuff to make that work. If "losing data" is a problem please provide the *reproducible* test case for that and we'll debug that.

I'm guessing most of your examples involve either a remote checksum being enabled or using NICs that don't support any tunnel offloads? Hardware needs to be able to identify where headers are in order to perform most of their offloads for TSO. We either have to parse to find them or we are provided with them by the stack. GSO can work around it as long as we don't stack checksum based offload with non-checksum of the same type.

Quoted 3 lines

mostIf for example you were to try and send a frame that had either an inner or outer GRE tunnel in addition to a UDP tunnel most NICs would probably screw it up.

Quoted 7 lines

Please be more precise. Obviously we're only talking about the few NICs that even support UDP tunnel offload so it's not most NICs. Also, there is a big difference between "probably" and "definitely"; no one has provided a single data point that that there is even an issue. For instance, looking a i40e I suspect this will work with GRE/UDP since the driver already deals with offsets and shouldn't care about intermediate levels of encapsulation.

I'm sorry I cannot be super precise as I hadn't looked that closely at the FOU or GUE code before. Honestly I suspect most people probably haven't.

So from what I can tell FOU and GUE isn't really even necessarily doing stacked tunnels. It looks like you support IPIP, SIT, or GRE. So in the case of IPIP and SIT for instance the only real difference between VXLAN and those tunnels with fou is that you don't have the VXLAN or inner Ethernet headers. So really you still only have two levels of headers. Even in the case of GRE you have that set after the outer UDP header so in that case GRE ends up being treated as a tunnel header since the outer transport offset was overwritten. If we had hardware that supported both UDP and GRE outer checksums it would cause a mess as the hardware would place the GRE checksum in the wrong spot.

So if anything all we probably would need to do is treat the FOU or GUE stuff as a special case. Basically if we end up having to do a GRO over a FOU or GUE instance maybe we need to knock the encap_mark back to 0 of it is at 1 and the next level is IPIP, SIT, or GRE because really it can just be treated as a UDP tunnel. Jesse's code is still needed to catch the case where someone is trying to do something like IPIP over VXLAN or whatever but it does seem like there should be some wiggle room for FOU or GUE.

- Alex

Quoted 137 lines · Alexander Duyck

Quoted 128 lines · Tom Herbert

Quoted 122 lines · Alexander Duyck

Quoted 108 lines · Tom Herbert

Quoted 99 lines · Alexander Duyck

Quoted 42 lines · Tom Herbert

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Quoted 5 lines

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Jesse does have a point. Drivers aren't checking for this kind of thing currently as the transmit side doesn't generate these kind of frames. The fact that GRO is makes things a bit more messy as we will really need to restructure the GSO code in order to handle it. As far as drivers testing for it I am pretty certain the i40e isn't. I would wonder if we need to add yet another GSO bit to indicate that we support multiple layers of encapsulation. I'm pretty sure the only way we could possibly handle it would be in software since what you are indicating is a indeterminate number of headers that all require updates.

Quoted 8 lines

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

Quoted 7 lines

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

The segmentation code isn't designed to handle more than 2 layers of headers. Currently we have the pointers for the inner headers and the outer headers. If you are talking about adding yet another level we would need additional pointers in the skbuff to handle them and we currently don't have them at present.

Quoted 6 lines

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 10 lines

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

Quoted 7 lines

This isn't about if drivers can handle it. It is about if the skbuff can handle it. The problem as it stands right now is that we start losing data once we go past 1 level of encapsulation. We only have the standard mac_header, network_header, transport_header, and then the inner set of the same pointers. If we try to go multiple levels deep we start losing data.

Quoted 4 lines

Huh? GUE/FOU has been running perfectly well with two levels of encapsulation for over a year now. We never had to add anything to skbuff to make that work. If "losing data" is a problem please provide the *reproducible* test case for that and we'll debug that.

I'm guessing most of your examples involve either a remote checksum being enabled or using NICs that don't support any tunnel offloads? Hardware needs to be able to identify where headers are in order to perform most of their offloads for TSO. We either have to parse to find them or we are provided with them by the stack. GSO can work around it as long as we don't stack checksum based offload with non-checksum of the same type.

Quoted 3 lines

mostIf for example you were to try and send a frame that had either an inner or outer GRE tunnel in addition to a UDP tunnel most NICs would probably screw it up.

Quoted 7 lines

Please be more precise. Obviously we're only talking about the few NICs that even support UDP tunnel offload so it's not most NICs. Also, there is a big difference between "probably" and "definitely"; no one has provided a single data point that that there is even an issue. For instance, looking a i40e I suspect this will work with GRE/UDP since the driver already deals with offsets and shouldn't care about intermediate levels of encapsulation.

Quoted 4 lines

I'm sorry I cannot be super precise as I hadn't looked that closely at the FOU or GUE code before. Honestly I suspect most people probably haven't.

Sorry, but one simple test would have identified this patch was a regression. I don't mind that bugs are introduced with new patches, but it is frustrating when testing of the patches is obviously inadequate and then we get the "it's your stuff that's broken" knee jerk reaction when a patch causes a regression for someone else.

Quoted 12 lines

So from what I can tell FOU and GUE isn't really even necessarily doing stacked tunnels. It looks like you support IPIP, SIT, or GRE. So in the case of IPIP and SIT for instance the only real difference between VXLAN and those tunnels with fou is that you don't have the VXLAN or inner Ethernet headers. So really you still only have two levels of headers. Even in the case of GRE you have that set after the outer UDP header so in that case GRE ends up being treated as a tunnel header since the outer transport offset was overwritten. If we had hardware that supported both UDP and GRE outer checksums it would cause a mess as the hardware would place the GRE checksum in the wrong spot.

Quoted 9 lines

So if anything all we probably would need to do is treat the FOU or GUE stuff as a special case. Basically if we end up having to do a GRO over a FOU or GUE instance maybe we need to knock the encap_mark back to 0 of it is at 1 and the next level is IPIP, SIT, or GRE because really it can just be treated as a UDP tunnel. Jesse's code is still needed to catch the case where someone is trying to do something like IPIP over VXLAN or whatever but it does seem like there should be some wiggle room for FOU or GUE.

Nothing is needed other than to revert this patch. There is no problem with GRO. You nor Jesse have not identified any tangible problem. If a driver really does had an issue with doing GRE/UDP with GSO then it can filter that in check_features (this is like 2 lines of code). But that has not been proven to be a problem, and I would expect that anyone who wants to fix that better run tests showing there is a problem.

Quoted 170 lines · Tom Herbert

Quoted 137 lines · Alexander Duyck

Quoted 128 lines · Tom Herbert

Quoted 122 lines · Alexander Duyck

Quoted 108 lines · Tom Herbert

Quoted 99 lines · Alexander Duyck

Quoted 42 lines · Tom Herbert

Quoted 34 lines · Jesse Gross

Quoted 24 lines · Tom Herbert

Quoted 5 lines · Jesse Gross

When drivers express support for TSO of encapsulated packets, they only mean that they can do it for one layer of encapsulation. Supporting additional levels would mean updating, at a minimum, more IP length fields and they are unaware of this.

This patch completely breaks GRO for FOU and GUE.

Quoted 10 lines

No encapsulation device expresses support for handling offloaded encapsulated packets, so we won't generate these types of frames in the transmit path. However, GRO doesn't have a check for multiple levels of encapsulation and will attempt to build them.

UDP tunnel GRO actually does prevent this situation but it only handles multiple UDP tunnels stacked on top of each other. This generalizes that solution to prevent any kind of tunnel stacking that would cause problems.

GUE and FOU regularly create packets that will be both GSO UDP tunnels and IPIP, SIT, GRE, etc. This is by design. There should be no ambiguity in the drivers as to what this means. For instance, if SKB_GSO_UDP_TUNNEL and SKB_GSO_GRE are set that is GRE/UDP packet, a driver can use ndo_features_check to validate.

Quoted 8 lines

So multiple levels of encapsulation with GRO is perfectly valid and I would suggest to simply revert this patch. The one potential issue we could have is the potential for GRO to construct a packet which is a UDP-encapsulation inside another encapsulation, like UDP-encap in GRE. In this case the GSO flags don't provide enough information to distinguish say between GRE/UDP (common case) and UDP/GRE (uncommon case). To make this clear we can set udp_mark in GRE, ipip, and sit but *not* check for it.

Quoted 6 lines

Generally speaking, multiple levels of encapsulation offload are not valid. I think this is pretty clear from the fact that none of the encapsulation drivers expose support for encapsulation offloads on transmit and the drivers supporting NETIF_F_GSO_GRE and NETIF_F_GSO_UDP_TUNNEL do not mean they can handle GRE in VXLAN.

Quoted 5 lines

Kernel software offload does support this combination just fine. Seriously, I've tested that more than a thousand times. This is a few HW implementations you're referring to. The limitations of these drivers should not dictate how we build the software-- it needs to work the other way around.

Jesse does have a point. Drivers aren't checking for this kind of thing currently as the transmit side doesn't generate these kind of frames. The fact that GRO is makes things a bit more messy as we will really need to restructure the GSO code in order to handle it. As far as drivers testing for it I am pretty certain the i40e isn't. I would wonder if we need to add yet another GSO bit to indicate that we support multiple layers of encapsulation. I'm pretty sure the only way we could possibly handle it would be in software since what you are indicating is a indeterminate number of headers that all require updates.

Quoted 8 lines

Quoted 8 lines

Asking drivers to assume that this combination of flags means FOU doesn't seem right to me. To the best of my knowledge, no driver uses ndo_feature_check to do validation of multiple tunnel offload flags since the assumption is that the stack will never try to do this. Since FOU is being treated as only a single level of encapsulation, I think it would be better to just advertise it that way on transmit (i.e. only set SKB_GSO_UDP_TUNNEL).

Quoted 7 lines

If it's not FOU it will be something else. Arbitrarily declaring multi-levels of encapsulation invalid is simply the wrong direction, we should be increasing generality and capabilities of the kernel not holding it down with artificial limits. This is why the generic TSO work that Alexander and Edward are looking at is so important-- if this flies then we can offload any combination of encapsulations with out protocol specific information.

The segmentation code isn't designed to handle more than 2 layers of headers. Currently we have the pointers for the inner headers and the outer headers. If you are talking about adding yet another level we would need additional pointers in the skbuff to handle them and we currently don't have them at present.

Quoted 6 lines

Quoted 5 lines

The change that you are suggesting would result in packets generated by GRO that cannot be handled properly on transmit in some cases and would likely end up being dropped or malformed. GRO is just an optimization and correctness must come first so we cannot use it if it might corrupt traffic.

Quoted 10 lines

That's (a few) drivers problem. It's no different than if they had decided that SKB_GSO_UDP_TUNNEL means vxlan, or they can support GRE in IPv4 offload but not GRE in IPv6, or they can only handle headers of a certain size, can't handle IPv6 ext. hdrs., etc. As I mentioned, the long term solution is to eliminate the GSO_ flags and use a generic segmentation offload interface. But in the interim, it is *incumbent* on drivers to determine if they can handle a GSO packet and the interfaces to do that exist. Restricting the capabilities of GRO just to appease those drivers is not right. Breaking existing GRO for their benefit is definitely not right.

Quoted 7 lines

This isn't about if drivers can handle it. It is about if the skbuff can handle it. The problem as it stands right now is that we start losing data once we go past 1 level of encapsulation. We only have the standard mac_header, network_header, transport_header, and then the inner set of the same pointers. If we try to go multiple levels deep we start losing data.

Quoted 4 lines

Huh? GUE/FOU has been running perfectly well with two levels of encapsulation for over a year now. We never had to add anything to skbuff to make that work. If "losing data" is a problem please provide the *reproducible* test case for that and we'll debug that.

I'm guessing most of your examples involve either a remote checksum being enabled or using NICs that don't support any tunnel offloads? Hardware needs to be able to identify where headers are in order to perform most of their offloads for TSO. We either have to parse to find them or we are provided with them by the stack. GSO can work around it as long as we don't stack checksum based offload with non-checksum of the same type.

Quoted 3 lines

mostIf for example you were to try and send a frame that had either an inner or outer GRE tunnel in addition to a UDP tunnel most NICs would probably screw it up.

Quoted 7 lines

Please be more precise. Obviously we're only talking about the few NICs that even support UDP tunnel offload so it's not most NICs. Also, there is a big difference between "probably" and "definitely"; no one has provided a single data point that that there is even an issue. For instance, looking a i40e I suspect this will work with GRE/UDP since the driver already deals with offsets and shouldn't care about intermediate levels of encapsulation.

Quoted 4 lines

I'm sorry I cannot be super precise as I hadn't looked that closely at the FOU or GUE code before. Honestly I suspect most people probably haven't.

Sorry, but one simple test would have identified this patch was a regression. I don't mind that bugs are introduced with new patches, but it is frustrating when testing of the patches is obviously inadequate and then we get the "it's your stuff that's broken" knee jerk reaction when a patch causes a regression for someone else.

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So from what I can tell FOU and GUE isn't really even necessarily doing stacked tunnels. It looks like you support IPIP, SIT, or GRE. So in the case of IPIP and SIT for instance the only real difference between VXLAN and those tunnels with fou is that you don't have the VXLAN or inner Ethernet headers. So really you still only have two levels of headers. Even in the case of GRE you have that set after the outer UDP header so in that case GRE ends up being treated as a tunnel header since the outer transport offset was overwritten. If we had hardware that supported both UDP and GRE outer checksums it would cause a mess as the hardware would place the GRE checksum in the wrong spot.

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So if anything all we probably would need to do is treat the FOU or GUE stuff as a special case. Basically if we end up having to do a GRO over a FOU or GUE instance maybe we need to knock the encap_mark back to 0 of it is at 1 and the next level is IPIP, SIT, or GRE because really it can just be treated as a UDP tunnel. Jesse's code is still needed to catch the case where someone is trying to do something like IPIP over VXLAN or whatever but it does seem like there should be some wiggle room for FOU or GUE.

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Nothing is needed other than to revert this patch. There is no problem with GRO. You nor Jesse have not identified any tangible problem. If a driver really does had an issue with doing GRE/UDP with GSO then it can filter that in check_features (this is like 2 lines of code). But that has not been proven to be a problem, and I would expect that anyone who wants to fix that better run tests showing there is a problem.

Let me try to give a very clear and specific example. Note that this is pure software and does not involve any hardware offloading.

* A packet is received that is encapsulated with two layers of GRE. It looks like this: Eth|IP|GRE|IP|GRE|IP|TCP
* The packet is processed through GRO successfully. skb->encapsulation bit is set and skb_shinfo(skb)->gso_type is set to SKB_GSO_GRE | SKB_GSO_TCPV4.
* The packet is bridged to an output device and is prepared for transmission. skb_gso_segment() is called to segment the packet.
* As we descent down the GSO code, we get to gre_gso_segment() for the first GRE header. skb->encapsulation is cleared and we keep going to the next header.
* We return to gre_gso_segment() again for the second GRE header. There is a check for skb->encapsulation being set but it is now clear. GSO processing is aborted.
* The packet is dropped.

Quoted 6 lines · Jesse Gross

* A packet is received that is encapsulated with two layers of GRE. It looks like this: Eth|IP|GRE|IP|GRE|IP|TCP
* The packet is processed through GRO successfully. skb->encapsulation bit is set and skb_shinfo(skb)->gso_type is set to SKB_GSO_GRE | SKB_GSO_TCPV4.
* The packet is bridged to an output device and is prepared for

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transmission. skb_gso_segment() is called to segment the packet.
* As we descent down the GSO code, we get to gre_gso_segment() for the first GRE header. skb->encapsulation is cleared and we keep going to the next header.
* We return to gre_gso_segment() again for the second GRE header. There is a check for skb->encapsulation being set but it is now clear. GSO processing is aborted.
* The packet is dropped.

If multiple level of GRE GSO is the problem then you are welcome to fix it after FOU is fixed and when net-next opens (GSO partial should fix this this anyway). But this is not at all the same problem as saying all multiple levels of encapsulation are invalid so we need to disallow that in GRO for everyone regardless of whether the packet is is being forwarded or some driver can't understand a certain valid combination.

Testing GUE is really not hard. There is no reason why GUE, Geneve, and VXLAN should not be tested each time a change is made to any of the common UDP tunneling code.

Configuring ipip-GUE can be done by:

./ip fou add port 6080 gue
./ip link add name tun1 type ipip remote 10.1.1.2 local 10.1.1.1 ttl 225 encap gue encap-sport auto encap-dport 6080 encap-csum encap-remcsum
ifconfig tun1 192.168.1.1
ip route add 192.168.1.0/24 dev tun1

Configuring gre-GUE is just s/ipip/gre/ of above.

./netperf -H 192.168.1.2 -t TCP_STREAM -l 100

Is good for showing showing regression in a single flow. You should see GSO/GRO being effective on both sides and perf should show only a minute amount of time in csum_partial assuming that your device has checksum offload for outer UDP (which should be about all).

./super_netperf 200 -H 192.168.1.2 -j -l 1 -t TCP_RR -- -r 1,1 -o TRANSACTION_RATE,P50_LATENCY,P90_LATENCY,P99_LATENCY

Is run to test pps. We're looking for no regression in tput, latency, or CPU utilization.

Next time you make changes to anything that affects common paths in tunnels please run these tests and report the results in the commit log so we can avoid regressions like this. You should also be running an equivalent battery of VXLAN tests. The configuration I use is:

./ip link add vxlan0 type vxlan id 10 group 224.10.10.10 ttl 10 dev eth0 udpcsum remcsumtx remcsumrx
ifconfig vxlan0 192.168.111.1
ip route add 192.168.111.0/24 dev vxlan0

Again we expect the same sort of results, GRO/GSO should be effective, csum_partial should not be getting significant tine, etc...

Generally speaking, multiple levels of encapsulation offload are not valid.

This series fixes a problem that was reported where encapsulated packets do not have their encapsulation offload markers stripped off when being decapsulated. This causes a significant performance drop if the packets are later retransmitted.

Fixing this revealed two other bugs which are also addressed as prerequisites:
* GRO can aggregate packets for multiple layers of encapsulation which the stack cannot properly handle.
* IPIP packets which are combined by GRO are not marked properly with their GSO type.

Note that this is based off the net-next tree as the current target for bug fixes.

v2: No code changes, just additional information in commit messages and
a new cover letter.