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596bef1d718d7a98def7945fad694c3ddbbbfef1
v1->v2: updated comments
v1: https://lore.kernel.org/bpf/20260322225124.14005-1-alexei.starovoitov@gmail.com/
The commit 6efbde200b ("bpf: Handle scalar spill vs all MISC in stacksafe()")
in stacksafe() only recognized full 64-bit scalar spills when
comparing stack states for equivalence during state pruning and
missed 32-bit scalar spill. When 32-bit scalar is spilled the
check_stack_write_fixed_off() -> save_register_state() calls
mark_stack_slot_misc() for slot[0-3], which preserves STACK_INVALID
and STACK_ZERO (on a fresh stack slot[0-3] remain STACK_INVALID),
sets slot[4-7] = STACK_SPILL, and updates spilled_ptr.
The im=4 path is only reached when im=0 fails: The loop at im=0 already
attempts the 64-bit scalar-spill/all-MISC check. If it matches, i advances
by 7, skipping the entire 8-byte slot. So im=4 is only reached when bytes
0-3 are neither a scalar spill nor all-MISC — they must pass individual
byte-by-byte comparison first. Then bytes 4-7 get the scalar-unit
treatment.
is_spilled_scalar_after(stack, 4): slot_type[4] == STACK_SPILL from a
64-bit spill would have been caught at im=0 (unless it's a pointer spill,
in which case spilled_ptr.type != SCALAR_VALUE -> returns false at im=4
too). A partial overwrite of a 64-bit spill invalidates the entire slot in
check_stack_write_fixed_off().
is_stack_misc_after(stack, 4): Only checks bytes 4-7 are MISC/INVALID,
returns &unbound_reg. Comparing two unbound regs via regsafe() is safe.
Changes to cilium programs:
File Program Insns (A) Insns (B) Insns (DIFF)
_______________ _________________________________ _________ _________ ________________
bpf_host.o cil_host_policy 49351 45811 -3540 (-7.17%)
bpf_host.o cil_to_host 2384 2270 -114 (-4.78%)
bpf_host.o cil_to_netdev 112051 100269 -11782 (-10.51%)
bpf_host.o tail_handle_ipv4_cont_from_host 61175 60910 -265 (-0.43%)
bpf_host.o tail_handle_ipv4_cont_from_netdev 9381 8873 -508 (-5.42%)
bpf_host.o tail_handle_ipv4_from_host 12994 7066 -5928 (-45.62%)
bpf_host.o tail_handle_ipv4_from_netdev 85015 59875 -25140 (-29.57%)
bpf_host.o tail_handle_ipv6_cont_from_host 24732 23527 -1205 (-4.87%)
bpf_host.o tail_handle_ipv6_cont_from_netdev 9463 8953 -510 (-5.39%)
bpf_host.o tail_handle_ipv6_from_host 12477 11787 -690 (-5.53%)
bpf_host.o tail_handle_ipv6_from_netdev 30814 30017 -797 (-2.59%)
bpf_host.o tail_handle_nat_fwd_ipv4 8943 8860 -83 (-0.93%)
bpf_host.o tail_handle_snat_fwd_ipv4 64716 61625 -3091 (-4.78%)
bpf_host.o tail_handle_snat_fwd_ipv6 48299 30797 -17502 (-36.24%)
bpf_host.o tail_ipv4_host_policy_ingress 21591 20017 -1574 (-7.29%)
bpf_host.o tail_ipv6_host_policy_ingress 21177 20693 -484 (-2.29%)
bpf_host.o tail_nodeport_nat_egress_ipv4 16588 16543 -45 (-0.27%)
bpf_host.o tail_nodeport_nat_ingress_ipv4 39200 36116 -3084 (-7.87%)
bpf_host.o tail_nodeport_nat_ingress_ipv6 50102 48003 -2099 (-4.19%)
bpf_lxc.o tail_handle_ipv4_cont 113092 96891 -16201 (-14.33%)
bpf_lxc.o tail_handle_ipv6 6727 6701 -26 (-0.39%)
bpf_lxc.o tail_handle_ipv6_cont 25567 21805 -3762 (-14.71%)
bpf_lxc.o tail_ipv4_ct_egress 28843 15970 -12873 (-44.63%)
bpf_lxc.o tail_ipv4_ct_ingress 16691 10213 -6478 (-38.81%)
bpf_lxc.o tail_ipv4_ct_ingress_policy_only 16691 10213 -6478 (-38.81%)
bpf_lxc.o tail_ipv4_policy 6776 6622 -154 (-2.27%)
bpf_lxc.o tail_ipv4_to_endpoint 7523 7219 -304 (-4.04%)
bpf_lxc.o tail_ipv6_ct_egress 10275 9999 -276 (-2.69%)
bpf_lxc.o tail_ipv6_ct_ingress 6466 6438 -28 (-0.43%)
bpf_lxc.o tail_ipv6_ct_ingress_policy_only 6466 6438 -28 (-0.43%)
bpf_lxc.o tail_ipv6_policy 6859 5159 -1700 (-24.78%)
bpf_lxc.o tail_ipv6_to_endpoint 7039 4427 -2612 (-37.11%)
bpf_lxc.o tail_nodeport_ipv6_dsr 1175 1033 -142 (-12.09%)
bpf_lxc.o tail_nodeport_nat_egress_ipv4 16318 16292 -26 (-0.16%)
bpf_lxc.o tail_nodeport_nat_ingress_ipv4 18907 18490 -417 (-2.21%)
bpf_lxc.o tail_nodeport_nat_ingress_ipv6 14624 14556 -68 (-0.46%)
bpf_lxc.o tail_nodeport_rev_dnat_ipv4 4776 4588 -188 (-3.94%)
bpf_overlay.o tail_handle_inter_cluster_revsnat 15733 15498 -235 (-1.49%)
bpf_overlay.o tail_handle_ipv4 124682 105717 -18965 (-15.21%)
bpf_overlay.o tail_handle_ipv6 16201 15801 -400 (-2.47%)
bpf_overlay.o tail_handle_snat_fwd_ipv4 21280 19323 -1957 (-9.20%)
bpf_overlay.o tail_handle_snat_fwd_ipv6 20824 20822 -2 (-0.01%)
bpf_overlay.o tail_nodeport_ipv6_dsr 1175 1033 -142 (-12.09%)
bpf_overlay.o tail_nodeport_nat_egress_ipv4 16293 16267 -26 (-0.16%)
bpf_overlay.o tail_nodeport_nat_ingress_ipv4 20841 20737 -104 (-0.50%)
bpf_overlay.o tail_nodeport_nat_ingress_ipv6 14678 14629 -49 (-0.33%)
bpf_sock.o cil_sock4_connect 1678 1623 -55 (-3.28%)
bpf_sock.o cil_sock4_sendmsg 1791 1736 -55 (-3.07%)
bpf_sock.o cil_sock6_connect 3641 3600 -41 (-1.13%)
bpf_sock.o cil_sock6_recvmsg 2048 1899 -149 (-7.28%)
bpf_sock.o cil_sock6_sendmsg 3755 3721 -34 (-0.91%)
bpf_wireguard.o tail_handle_ipv4 31180 27484 -3696 (-11.85%)
bpf_wireguard.o tail_handle_ipv6 12095 11760 -335 (-2.77%)
bpf_wireguard.o tail_nodeport_ipv6_dsr 1232 1094 -138 (-11.20%)
bpf_wireguard.o tail_nodeport_nat_egress_ipv4 16071 16061 -10 (-0.06%)
bpf_wireguard.o tail_nodeport_nat_ingress_ipv4 20804 20565 -239 (-1.15%)
bpf_wireguard.o tail_nodeport_nat_ingress_ipv6 13490 12224 -1266 (-9.38%)
bpf_xdp.o tail_lb_ipv4 49695 42673 -7022 (-14.13%)
bpf_xdp.o tail_lb_ipv6 122683 87896 -34787 (-28.36%)
bpf_xdp.o tail_nodeport_ipv6_dsr 1833 1862 +29 (+1.58%)
bpf_xdp.o tail_nodeport_nat_egress_ipv4 6999 6990 -9 (-0.13%)
bpf_xdp.o tail_nodeport_nat_ingress_ipv4 28903 28780 -123 (-0.43%)
bpf_xdp.o tail_nodeport_nat_ingress_ipv6 200361 197771 -2590 (-1.29%)
bpf_xdp.o tail_nodeport_rev_dnat_ipv4 4606 4454 -152 (-3.30%)
Changes to sched-ext:
File Program Insns (A) Insns (B) Insns (DIFF)
_________________________ ________________ _________ _________ _______________
scx_arena_selftests.bpf.o arena_selftest 236305 236251 -54 (-0.02%)
scx_chaos.bpf.o chaos_dispatch 12282 8013 -4269 (-34.76%)
scx_chaos.bpf.o chaos_enqueue 11398 7126 -4272 (-37.48%)
scx_chaos.bpf.o chaos_init 3854 3828 -26 (-0.67%)
scx_flash.bpf.o flash_init 1015 979 -36 (-3.55%)
scx_flatcg.bpf.o fcg_dispatch 1143 1100 -43 (-3.76%)
scx_lavd.bpf.o lavd_enqueue 35487 35472 -15 (-0.04%)
scx_lavd.bpf.o lavd_init 21127 21107 -20 (-0.09%)
scx_p2dq.bpf.o p2dq_enqueue 10210 7854 -2356 (-23.08%)
scx_p2dq.bpf.o p2dq_init 3233 3207 -26 (-0.80%)
scx_qmap.bpf.o qmap_init 20285 20230 -55 (-0.27%)
scx_rusty.bpf.o rusty_select_cpu 1165 1148 -17 (-1.46%)
scxtop.bpf.o on_sched_switch 2369 2355 -14 (-0.59%)
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260323022410.75444-1-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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