[PATCH bpf-next v4 0/6] Mixing bpf2bpf and tailcalls for RV64

[Pu Lehui]

From: Pu Lehui <pulehui@xxxxxxxxxx>

In the current RV64 JIT, if we just don't initialize the TCC in subprog,
the TCC can be propagated from the parent process to the subprocess, but
the updated TCC of the parent process cannot be restored when the
subprocess exits. Since the RV64 TCC is initialized before saving the
callee saved registers into the stack, we cannot use the callee saved
register to pass the TCC, otherwise the original value of the callee
saved register will be destroyed. So we implemented mixing bpf2bpf and
tailcalls similar to x86_64, i.e. using a non-callee saved register to
transfer the TCC between functions, and saving that register to the
stack to protect the TCC value. As for the tailcall hierarchy issue,
inspired by the s390's low-overhead approach, we store TCC from
RV_REG_TCC back to stack after calling bpf2bpf call or calling orig bpf
func in bpf trampoline.

In addition, some code cleans are also attached to this patchset.

Tests test_bpf.ko and test_verifier have passed, as well as the relative
testcases of test_progs*.

v4:
- Fix tailcall hierarchy issue.
- use is_struct_ops_tramp helper in bpf trampoline

v3: https://lore.kernel.org/bpf/20240201083351.943121-1-pulehui@xxxxxxxxxxxxxxx
- Remove duplicate RV_REG_TCC load in epiloguei. (Björn Töpel)

v2: https://lore.kernel.org/bpf/20240130040958.230673-1-pulehui@xxxxxxxxxxxxxxx
- Fix emit restore RV_REG_TCC double times when `flags &
  BPF_TRAMP_F_CALL_ORIG`
- Use bpf_is_subprog helper

v1: https://lore.kernel.org/bpf/20230919035711.3297256-1-pulehui@xxxxxxxxxxxxxxx

Pu Lehui (6):
  bpf: Extract the is_struct_ops_tramp helper
  riscv, bpf: Remove redundant ctx->offset initialization
  riscv, bpf: Using kvzalloc_objs to allocate cache buffer
  riscv, bpf: Add RV_TAILCALL_OFFSET macro to format tailcall offset
  riscv, bpf: Mixing bpf2bpf and tailcalls
  selftests/bpf: Remove tailcalls tests from DENYLIST.riscv64

 arch/arm64/net/bpf_jit_comp.c                |   6 -
 arch/loongarch/net/bpf_jit.c                 |   2 +-
 arch/riscv/net/bpf_jit.h                     |   1 +
 arch/riscv/net/bpf_jit_comp64.c              | 120 +++++++++----------
 arch/riscv/net/bpf_jit_core.c                |   9 +-
 include/linux/bpf.h                          |   6 +
 tools/testing/selftests/bpf/DENYLIST.riscv64 |   1 -
 7 files changed, 68 insertions(+), 77 deletions(-)

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2.34.1