Re: [RFC PATCH bpf-next v2 0/4] bpf, x64: Fix tailcall hierarchy

[Leon Hwang <hffilwlqm@gmail.com>]

PING

On 11/10/23 23:27, Leon Hwang wrote:
> This patchset fixes a tailcall hierarchy issue with a better solution than v1[0].
> 
> v1 solution stores tail_call_cnt on the stack of bpf prog:
> 
>     |  STACK  |
>     +---------+ RBP
>     |         |
>     |         |
>     |         |
>  +--| tcc_ptr |
>  +->|   tcc   |
>     |   rbx   |
>     +---------+ RSP
> 
> v2 solution stores tail_call_cnt on the stack of bpf prog's caller:
> 
>     |  STACK  |
>     |         |
>     |   rip   |
>  +->|   tcc   |
>  |  |   rip   |
>  |  |   rbp   |
>  |  +---------+ RBP
>  |  |         |
>  |  |         |
>  |  |         |
>  +--| tcc_ptr |
>     |   rbx   |
>     +---------+ RSP
> 
> With this change, it requires less instructions to resolve this issue.
> 
> For more resolving details, please read the following patches.
> 
> The issue is confirmed in the discussions of "bpf, x64: Fix tailcall infinite
> loop"[1].
> 
> Currently, I only resolve this issue on x86. The ones on arm64, s390x and
> loongarch are waiting to be resolved. So, the ci pipeline fails to run for this
> issue fixing.
> 
> Hopefully, this issue on s390x and arm64 will be resolved soon.
> 
> v1 -> v2:
>   * address comments from Stanislav
>     * Separate moving emit_nops() as first patch.
> 
> Links:
> [0] https://lore.kernel.org/bpf/20231005145814.83122-1-hffilwlqm@gmail.com/
> [1] https://lore.kernel.org/bpf/6203dd01-789d-f02c-5293-def4c1b18aef@gmail.com/
> 
> Leon Hwang (4):
>   bpf, x64: Emit nops for X86_PATCH
>   bpf, x64: Fix tailcall hierarchy
>   bpf, x64: Load tail_call_cnt pointer
>   selftests/bpf: Add testcases for tailcall hierarchy fixing
> 
>  arch/x86/net/bpf_jit_comp.c                   |  99 +++--
>  .../selftests/bpf/prog_tests/tailcalls.c      | 418 ++++++++++++++++++
>  .../bpf/progs/tailcall_bpf2bpf_hierarchy1.c   |  34 ++
>  .../bpf/progs/tailcall_bpf2bpf_hierarchy2.c   |  55 +++
>  .../bpf/progs/tailcall_bpf2bpf_hierarchy3.c   |  46 ++
>  5 files changed, 606 insertions(+), 46 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy1.c
>  create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c
>  create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy3.c
> 
> 
> base-commit: 644b54d80d572438a815c05b1bab2b7871e1e5a1