linux-stable.git/Documentation/networking/ip-sysctl.rst, branch v6.2 Linux kernel stable tree sctp: add sysctl net.sctp.l3mdev_accept 2022-11-18T11:42:54+00:00 Xin Long lucien.xin@gmail.com 2022-11-16T20:01:21+00:00 b712d0328c2c3ab456847f29f711e785f70cd8a5 This patch is to add sysctl net.sctp.l3mdev_accept to allow users to change the pernet global l3mdev_accept. Signed-off-by: Xin Long <lucien.xin@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
This patch is to add sysctl net.sctp.l3mdev_accept to allow
users to change the pernet global l3mdev_accept.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
udp: Introduce optional per-netns hash table. 2022-11-16T09:43:35+00:00 Kuniyuki Iwashima kuniyu@amazon.com 2022-11-14T21:57:57+00:00 9804985bf27f8fbcf0d96c7435b5ad94a2a6ea20 The maximum hash table size is 64K due to the nature of the protocol. [0] It's smaller than TCP, and fewer sockets can cause a performance drop. On an EC2 c5.24xlarge instance (192 GiB memory), after running iperf3 in different netns, creating 32Mi sockets without data transfer in the root netns causes regression for the iperf3's connection. uhash_entries sockets length Gbps 64K 1 1 5.69 1Mi 16 5.27 2Mi 32 4.90 4Mi 64 4.09 8Mi 128 2.96 16Mi 256 2.06 32Mi 512 1.12 The per-netns hash table breaks the lengthy lists into shorter ones. It is useful on a multi-tenant system with thousands of netns. With smaller hash tables, we can look up sockets faster, isolate noisy neighbours, and reduce lock contention. The max size of the per-netns table is 64K as well. This is because the possible hash range by udp_hashfn() always fits in 64K within the same netns and we cannot make full use of the whole buckets larger than 64K. /* 0 < num < 64K -> X < hash < X + 64K */ (num + net_hash_mix(net)) & mask; Also, the min size is 128. We use a bitmap to search for an available port in udp_lib_get_port(). To keep the bitmap on the stack and not fire the CONFIG_FRAME_WARN error at build time, we round up the table size to 128. The sysctl usage is the same with TCP: $ dmesg | cut -d ' ' -f 6- | grep "UDP hash" UDP hash table entries: 65536 (order: 9, 2097152 bytes, vmalloc) # sysctl net.ipv4.udp_hash_entries net.ipv4.udp_hash_entries = 65536 # can be changed by uhash_entries # sysctl net.ipv4.udp_child_hash_entries net.ipv4.udp_child_hash_entries = 0 # disabled by default # ip netns add test1 # ip netns exec test1 sysctl net.ipv4.udp_hash_entries net.ipv4.udp_hash_entries = -65536 # share the global table # sysctl -w net.ipv4.udp_child_hash_entries=100 net.ipv4.udp_child_hash_entries = 100 # ip netns add test2 # ip netns exec test2 sysctl net.ipv4.udp_hash_entries net.ipv4.udp_hash_entries = 128 # own a per-netns table with 2^n buckets We could optimise the hash table lookup/iteration further by removing the netns comparison for the per-netns one in the future. Also, we could optimise the sparse udp_hslot layout by putting it in udp_table. [0]: https://lore.kernel.org/netdev/4ACC2815.7010101@gmail.com/ Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
The maximum hash table size is 64K due to the nature of the protocol. [0]
It's smaller than TCP, and fewer sockets can cause a performance drop.

On an EC2 c5.24xlarge instance (192 GiB memory), after running iperf3 in
different netns, creating 32Mi sockets without data transfer in the root
netns causes regression for the iperf3's connection.

  uhash_entries		sockets		length		Gbps
	    64K		      1		     1		5.69
			    1Mi		    16		5.27
			    2Mi		    32		4.90
			    4Mi		    64		4.09
			    8Mi		   128		2.96
			   16Mi		   256		2.06
			   32Mi		   512		1.12

The per-netns hash table breaks the lengthy lists into shorter ones.  It is
useful on a multi-tenant system with thousands of netns.  With smaller hash
tables, we can look up sockets faster, isolate noisy neighbours, and reduce
lock contention.

The max size of the per-netns table is 64K as well.  This is because the
possible hash range by udp_hashfn() always fits in 64K within the same
netns and we cannot make full use of the whole buckets larger than 64K.

  /* 0 < num < 64K  ->  X < hash < X + 64K */
  (num + net_hash_mix(net)) & mask;

Also, the min size is 128.  We use a bitmap to search for an available
port in udp_lib_get_port().  To keep the bitmap on the stack and not
fire the CONFIG_FRAME_WARN error at build time, we round up the table
size to 128.

The sysctl usage is the same with TCP:

  $ dmesg | cut -d ' ' -f 6- | grep "UDP hash"
  UDP hash table entries: 65536 (order: 9, 2097152 bytes, vmalloc)

  # sysctl net.ipv4.udp_hash_entries
  net.ipv4.udp_hash_entries = 65536  # can be changed by uhash_entries

  # sysctl net.ipv4.udp_child_hash_entries
  net.ipv4.udp_child_hash_entries = 0  # disabled by default

  # ip netns add test1
  # ip netns exec test1 sysctl net.ipv4.udp_hash_entries
  net.ipv4.udp_hash_entries = -65536  # share the global table

  # sysctl -w net.ipv4.udp_child_hash_entries=100
  net.ipv4.udp_child_hash_entries = 100

  # ip netns add test2
  # ip netns exec test2 sysctl net.ipv4.udp_hash_entries
  net.ipv4.udp_hash_entries = 128  # own a per-netns table with 2^n buckets

We could optimise the hash table lookup/iteration further by removing
the netns comparison for the per-netns one in the future.  Also, we
could optimise the sparse udp_hslot layout by putting it in udp_table.

[0]: https://lore.kernel.org/netdev/4ACC2815.7010101@gmail.com/

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
tcp: add sysctls for TCP PLB parameters 2022-10-28T09:47:42+00:00 Mubashir Adnan Qureshi mubashirq@google.com 2022-10-26T13:51:11+00:00 bd456f283b66704920fae8e655ebc769cb743420 PLB (Protective Load Balancing) is a host based mechanism for load balancing across switch links. It leverages congestion signals(e.g. ECN) from transport layer to randomly change the path of the connection experiencing congestion. PLB changes the path of the connection by changing the outgoing IPv6 flow label for IPv6 connections (implemented in Linux by calling sk_rethink_txhash()). Because of this implementation mechanism, PLB can currently only work for IPv6 traffic. For more information, see the SIGCOMM 2022 paper: https://doi.org/10.1145/3544216.3544226 This commit adds new sysctl knobs and sets their default values for TCP PLB. Signed-off-by: Mubashir Adnan Qureshi <mubashirq@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
PLB (Protective Load Balancing) is a host based mechanism for load
balancing across switch links. It leverages congestion signals(e.g. ECN)
from transport layer to randomly change the path of the connection
experiencing congestion. PLB changes the path of the connection by
changing the outgoing IPv6 flow label for IPv6 connections (implemented
in Linux by calling sk_rethink_txhash()). Because of this implementation
mechanism, PLB can currently only work for IPv6 traffic. For more
information, see the SIGCOMM 2022 paper:
  https://doi.org/10.1145/3544216.3544226

This commit adds new sysctl knobs and sets their default values for
TCP PLB.

Signed-off-by: Mubashir Adnan Qureshi <mubashirq@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
tcp: Introduce optional per-netns ehash. 2022-09-20T17:21:50+00:00 Kuniyuki Iwashima kuniyu@amazon.com 2022-09-08T01:10:22+00:00 d1e5e6408b305ff78b825d437df8d3f77e82a4be The more sockets we have in the hash table, the longer we spend looking up the socket. While running a number of small workloads on the same host, they penalise each other and cause performance degradation. The root cause might be a single workload that consumes much more resources than the others. It often happens on a cloud service where different workloads share the same computing resource. On EC2 c5.24xlarge instance (196 GiB memory and 524288 (1Mi / 2) ehash entries), after running iperf3 in different netns, creating 24Mi sockets without data transfer in the root netns causes about 10% performance regression for the iperf3's connection. thash_entries sockets length Gbps 524288 1 1 50.7 24Mi 48 45.1 It is basically related to the length of the list of each hash bucket. For testing purposes to see how performance drops along the length, I set 131072 (1Mi / 8) to thash_entries, and here's the result. thash_entries sockets length Gbps 131072 1 1 50.7 1Mi 8 49.9 2Mi 16 48.9 4Mi 32 47.3 8Mi 64 44.6 16Mi 128 40.6 24Mi 192 36.3 32Mi 256 32.5 40Mi 320 27.0 48Mi 384 25.0 To resolve the socket lookup degradation, we introduce an optional per-netns hash table for TCP, but it's just ehash, and we still share the global bhash, bhash2 and lhash2. With a smaller ehash, we can look up non-listener sockets faster and isolate such noisy neighbours. In addition, we can reduce lock contention. We can control the ehash size by a new sysctl knob. However, depending on workloads, it will require very sensitive tuning, so we disable the feature by default (net.ipv4.tcp_child_ehash_entries == 0). Moreover, we can fall back to using the global ehash in case we fail to allocate enough memory for a new ehash. The maximum size is 16Mi, which is large enough that even if we have 48Mi sockets, the average list length is 3, and regression would be less than 1%. We can check the current ehash size by another read-only sysctl knob, net.ipv4.tcp_ehash_entries. A negative value means the netns shares the global ehash (per-netns ehash is disabled or failed to allocate memory). # dmesg | cut -d ' ' -f 5- | grep "established hash" TCP established hash table entries: 524288 (order: 10, 4194304 bytes, vmalloc hugepage) # sysctl net.ipv4.tcp_ehash_entries net.ipv4.tcp_ehash_entries = 524288 # can be changed by thash_entries # sysctl net.ipv4.tcp_child_ehash_entries net.ipv4.tcp_child_ehash_entries = 0 # disabled by default # ip netns add test1 # ip netns exec test1 sysctl net.ipv4.tcp_ehash_entries net.ipv4.tcp_ehash_entries = -524288 # share the global ehash # sysctl -w net.ipv4.tcp_child_ehash_entries=100 net.ipv4.tcp_child_ehash_entries = 100 # ip netns add test2 # ip netns exec test2 sysctl net.ipv4.tcp_ehash_entries net.ipv4.tcp_ehash_entries = 128 # own a per-netns ehash with 2^n buckets When more than two processes in the same netns create per-netns ehash concurrently with different sizes, we need to guarantee the size in one of the following ways: 1) Share the global ehash and create per-netns ehash First, unshare() with tcp_child_ehash_entries==0. It creates dedicated netns sysctl knobs where we can safely change tcp_child_ehash_entries and clone()/unshare() to create a per-netns ehash. 2) Control write on sysctl by BPF We can use BPF_PROG_TYPE_CGROUP_SYSCTL to allow/deny read/write on sysctl knobs. Note that the global ehash allocated at the boot time is spread over available NUMA nodes, but inet_pernet_hashinfo_alloc() will allocate pages for each per-netns ehash depending on the current process's NUMA policy. By default, the allocation is done in the local node only, so the per-netns hash table could fully reside on a random node. Thus, depending on the NUMA policy the netns is created with and the CPU the current thread is running on, we could see some performance differences for highly optimised networking applications. Note also that the default values of two sysctl knobs depend on the ehash size and should be tuned carefully: tcp_max_tw_buckets : tcp_child_ehash_entries / 2 tcp_max_syn_backlog : max(128, tcp_child_ehash_entries / 128) As a bonus, we can dismantle netns faster. Currently, while destroying netns, we call inet_twsk_purge(), which walks through the global ehash. It can be potentially big because it can have many sockets other than TIME_WAIT in all netns. Splitting ehash changes that situation, where it's only necessary for inet_twsk_purge() to clean up TIME_WAIT sockets in each netns. With regard to this, we do not free the per-netns ehash in inet_twsk_kill() to avoid UAF while iterating the per-netns ehash in inet_twsk_purge(). Instead, we do it in tcp_sk_exit_batch() after calling tcp_twsk_purge() to keep it protocol-family-independent. In the future, we could optimise ehash lookup/iteration further by removing netns comparison for the per-netns ehash. Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
The more sockets we have in the hash table, the longer we spend looking
up the socket.  While running a number of small workloads on the same
host, they penalise each other and cause performance degradation.

The root cause might be a single workload that consumes much more
resources than the others.  It often happens on a cloud service where
different workloads share the same computing resource.

On EC2 c5.24xlarge instance (196 GiB memory and 524288 (1Mi / 2) ehash
entries), after running iperf3 in different netns, creating 24Mi sockets
without data transfer in the root netns causes about 10% performance
regression for the iperf3's connection.

 thash_entries		sockets		length		Gbps
	524288		      1		     1		50.7
			   24Mi		    48		45.1

It is basically related to the length of the list of each hash bucket.
For testing purposes to see how performance drops along the length,
I set 131072 (1Mi / 8) to thash_entries, and here's the result.

 thash_entries		sockets		length		Gbps
        131072		      1		     1		50.7
			    1Mi		     8		49.9
			    2Mi		    16		48.9
			    4Mi		    32		47.3
			    8Mi		    64		44.6
			   16Mi		   128		40.6
			   24Mi		   192		36.3
			   32Mi		   256		32.5
			   40Mi		   320		27.0
			   48Mi		   384		25.0

To resolve the socket lookup degradation, we introduce an optional
per-netns hash table for TCP, but it's just ehash, and we still share
the global bhash, bhash2 and lhash2.

With a smaller ehash, we can look up non-listener sockets faster and
isolate such noisy neighbours.  In addition, we can reduce lock contention.

We can control the ehash size by a new sysctl knob.  However, depending
on workloads, it will require very sensitive tuning, so we disable the
feature by default (net.ipv4.tcp_child_ehash_entries == 0).  Moreover,
we can fall back to using the global ehash in case we fail to allocate
enough memory for a new ehash.  The maximum size is 16Mi, which is large
enough that even if we have 48Mi sockets, the average list length is 3,
and regression would be less than 1%.

We can check the current ehash size by another read-only sysctl knob,
net.ipv4.tcp_ehash_entries.  A negative value means the netns shares
the global ehash (per-netns ehash is disabled or failed to allocate
memory).

  # dmesg | cut -d ' ' -f 5- | grep "established hash"
  TCP established hash table entries: 524288 (order: 10, 4194304 bytes, vmalloc hugepage)

  # sysctl net.ipv4.tcp_ehash_entries
  net.ipv4.tcp_ehash_entries = 524288  # can be changed by thash_entries

  # sysctl net.ipv4.tcp_child_ehash_entries
  net.ipv4.tcp_child_ehash_entries = 0  # disabled by default

  # ip netns add test1
  # ip netns exec test1 sysctl net.ipv4.tcp_ehash_entries
  net.ipv4.tcp_ehash_entries = -524288  # share the global ehash

  # sysctl -w net.ipv4.tcp_child_ehash_entries=100
  net.ipv4.tcp_child_ehash_entries = 100

  # ip netns add test2
  # ip netns exec test2 sysctl net.ipv4.tcp_ehash_entries
  net.ipv4.tcp_ehash_entries = 128  # own a per-netns ehash with 2^n buckets

When more than two processes in the same netns create per-netns ehash
concurrently with different sizes, we need to guarantee the size in
one of the following ways:

  1) Share the global ehash and create per-netns ehash

  First, unshare() with tcp_child_ehash_entries==0.  It creates dedicated
  netns sysctl knobs where we can safely change tcp_child_ehash_entries
  and clone()/unshare() to create a per-netns ehash.

  2) Control write on sysctl by BPF

  We can use BPF_PROG_TYPE_CGROUP_SYSCTL to allow/deny read/write on
  sysctl knobs.

Note that the global ehash allocated at the boot time is spread over
available NUMA nodes, but inet_pernet_hashinfo_alloc() will allocate
pages for each per-netns ehash depending on the current process's NUMA
policy.  By default, the allocation is done in the local node only, so
the per-netns hash table could fully reside on a random node.  Thus,
depending on the NUMA policy the netns is created with and the CPU the
current thread is running on, we could see some performance differences
for highly optimised networking applications.

Note also that the default values of two sysctl knobs depend on the ehash
size and should be tuned carefully:

  tcp_max_tw_buckets  : tcp_child_ehash_entries / 2
  tcp_max_syn_backlog : max(128, tcp_child_ehash_entries / 128)

As a bonus, we can dismantle netns faster.  Currently, while destroying
netns, we call inet_twsk_purge(), which walks through the global ehash.
It can be potentially big because it can have many sockets other than
TIME_WAIT in all netns.  Splitting ehash changes that situation, where
it's only necessary for inet_twsk_purge() to clean up TIME_WAIT sockets
in each netns.

With regard to this, we do not free the per-netns ehash in inet_twsk_kill()
to avoid UAF while iterating the per-netns ehash in inet_twsk_purge().
Instead, we do it in tcp_sk_exit_batch() after calling tcp_twsk_purge() to
keep it protocol-family-independent.

In the future, we could optimise ehash lookup/iteration further by removing
netns comparison for the per-netns ehash.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
tcp: make global challenge ack rate limitation per net-ns and default disabled 2022-09-01T02:56:48+00:00 Eric Dumazet edumazet@google.com 2022-08-30T18:56:56+00:00 79e3602caa6f9d59c4f66a268407080496dae408 Because per host rate limiting has been proven problematic (side channel attacks can be based on it), per host rate limiting of challenge acks ideally should be per netns and turned off by default. This is a long due followup of following commits: 083ae308280d ("tcp: enable per-socket rate limiting of all 'challenge acks'") f2b2c582e824 ("tcp: mitigate ACK loops for connections as tcp_sock") 75ff39ccc1bd ("tcp: make challenge acks less predictable") Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Jason Baron <jbaron@akamai.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Because per host rate limiting has been proven problematic (side channel
attacks can be based on it), per host rate limiting of challenge acks ideally
should be per netns and turned off by default.

This is a long due followup of following commits:

083ae308280d ("tcp: enable per-socket rate limiting of all 'challenge acks'")
f2b2c582e824 ("tcp: mitigate ACK loops for connections as tcp_sock")
75ff39ccc1bd ("tcp: make challenge acks less predictable")

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jason Baron <jbaron@akamai.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Documentation: Describe net.ipv4.tcp_reflect_tos. 2022-07-29T11:10:21+00:00 Guillaume Nault gnault@redhat.com 2022-07-27T11:18:21+00:00 1c7249e4af8e1aea1c47739ec9dc63cc828b5d08 The tcp_reflect_tos option was introduced in Linux 5.10 but was still undocumented. Signed-off-by: Guillaume Nault <gnault@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
The tcp_reflect_tos option was introduced in Linux 5.10 but was still
undocumented.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2022-07-29T01:21:16+00:00 Jakub Kicinski kuba@kernel.org 2022-07-29T01:21:16+00:00 272ac32f566e3f925b20c231a2b30f6893aa258a No conflicts. Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
No conflicts.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Documentation: fix sctp_wmem in ip-sysctl.rst 2022-07-24T20:41:58+00:00 Xin Long lucien.xin@gmail.com 2022-07-21T14:35:46+00:00 aa709da0e032cee7c202047ecd75f437bb0126ed Since commit 1033990ac5b2 ("sctp: implement memory accounting on tx path"), SCTP has supported memory accounting on tx path where 'sctp_wmem' is used by sk_wmem_schedule(). So we should fix the description for this option in ip-sysctl.rst accordingly. v1->v2: - Improve the description as Marcelo suggested. Fixes: 1033990ac5b2 ("sctp: implement memory accounting on tx path") Signed-off-by: Xin Long <lucien.xin@gmail.com> Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
Since commit 1033990ac5b2 ("sctp: implement memory accounting on tx path"),
SCTP has supported memory accounting on tx path where 'sctp_wmem' is used
by sk_wmem_schedule(). So we should fix the description for this option in
ip-sysctl.rst accordingly.

v1->v2:
  - Improve the description as Marcelo suggested.

Fixes: 1033990ac5b2 ("sctp: implement memory accounting on tx path")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2022-07-21T20:03:39+00:00 Jakub Kicinski kuba@kernel.org 2022-07-21T20:03:39+00:00 6e0e846ee2ab01bc44254e6a0a6a6a0db1cba16d No conflicts. Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
No conflicts.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Documentation: fix udp_wmem_min in ip-sysctl.rst 2022-07-20T00:34:53+00:00 Xin Long lucien.xin@gmail.com 2022-07-18T17:56:59+00:00 c6b10de537b904fb70522d8cc4600c2f11246c93 UDP doesn't support tx memory accounting, and sysctl udp_wmem_min is not really used anywhere. So we should fix the description in ip-sysctl.rst accordingly. Fixes: 95766fff6b9a ("[UDP]: Add memory accounting.") Signed-off-by: Xin Long <lucien.xin@gmail.com> Link: https://lore.kernel.org/r/c880a963d9b1fb5f442ae3c9e4dfa70d45296a16.1658167019.git.lucien.xin@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
UDP doesn't support tx memory accounting, and sysctl udp_wmem_min
is not really used anywhere. So we should fix the description in
ip-sysctl.rst accordingly.

Fixes: 95766fff6b9a ("[UDP]: Add memory accounting.")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/c880a963d9b1fb5f442ae3c9e4dfa70d45296a16.1658167019.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>