selftests/bpf: Add test for sk->sk_bypass_prot_mem.

The test does the following for IPv4/IPv6 x TCP/UDP sockets
with/without sk->sk_bypass_prot_mem, which can be turned on by
net.core.bypass_prot_mem or bpf_setsockopt(SK_BPF_BYPASS_PROT_MEM).

  1. Create socket pairs
  2. Send NR_PAGES (32) of data (TCP consumes around 35 pages,
     and UDP consuems 66 pages due to skb overhead)
  3. Read memory_allocated from sk->sk_prot->memory_allocated and
     sk->sk_prot->memory_per_cpu_fw_alloc
  4. Check if unread data is charged to memory_allocated

If sk->sk_bypass_prot_mem is set, memory_allocated should not be
changed, but we allow a small error (up to 10 pages) in case
other processes on the host use some amounts of TCP/UDP memory.

The amount of allocated pages are buffered to per-cpu variable
{tcp,udp}_memory_per_cpu_fw_alloc up to +/- net.core.mem_pcpu_rsv
before reported to {tcp,udp}_memory_allocated.

At 3., memory_allocated is calculated from the 2 variables at
fentry of socket create function.

We drain the receive queue only for UDP before close() because UDP
recv queue is destroyed after RCU grace period.  When I printed
memory_allocated, UDP bypass cases sometimes saw the no-bypass
case's leftover, but it's still in the small error range (<10 pages).

  bpf_trace_printk: memory_allocated: 0   <-- TCP no-bypass
  bpf_trace_printk: memory_allocated: 35
  bpf_trace_printk: memory_allocated: 0   <-- TCP w/ sysctl
  bpf_trace_printk: memory_allocated: 0
  bpf_trace_printk: memory_allocated: 0   <-- TCP w/ bpf
  bpf_trace_printk: memory_allocated: 0
  bpf_trace_printk: memory_allocated: 0   <-- UDP no-bypass
  bpf_trace_printk: memory_allocated: 66
  bpf_trace_printk: memory_allocated: 2   <-- UDP w/ sysctl (2 pages leftover)
  bpf_trace_printk: memory_allocated: 2
  bpf_trace_printk: memory_allocated: 2   <-- UDP w/ bpf (2 pages leftover)
  bpf_trace_printk: memory_allocated: 2

We prefer finishing tests faster than oversleeping for call_rcu()
 + sk_destruct().

The test completes within 2s on QEMU (64 CPUs) w/ KVM.

  # time ./test_progs -t sk_bypass
  #371/1   sk_bypass_prot_mem/TCP  :OK
  #371/2   sk_bypass_prot_mem/UDP  :OK
  #371/3   sk_bypass_prot_mem/TCPv6:OK
  #371/4   sk_bypass_prot_mem/UDPv6:OK
  #371     sk_bypass_prot_mem:OK
  Summary: 1/4 PASSED, 0 SKIPPED, 0 FAILED

  real	0m1.481s
  user	0m0.181s
  sys	0m0.441s

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Link: https://patch.msgid.link/20251014235604.3057003-7-kuniyu@google.com

0 files changed, 0 insertions, 0 deletions