Re: [PATCH bpf-next v2 00/15] bpf: Support new insns from cpu v4

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2023-07-12 at 23:07 -0700, Yonghong Song wrote:
> > In previous discussion ([1]), it is agreed that we should introduce
> > cpu version 4 (llvm flag -mcpu=v4) which contains some instructions
> > which can simplify code, make code easier to understand, fix the
> > existing problem, or simply for feature completeness. More specifically,
> > the following new insns are proposed:
> >   . sign extended load
> >   . sign extended mov
> >   . bswap
> >   . signed div/mod
> >   . ja with 32-bit offset
> > 
> > This patch set added kernel support for insns proposed in [1] except
> > BPF_ST which already has full kernel support. Beside the above proposed
> > insns, LLVM will generate BPF_ST insn as well under -mcpu=v4 ([2]).
> > 
> > The patchset implements interpreter and jit support for these new
> > insns as well as necessary verifier support.

Hi Yonghong,

Sorry for delayed response, I'm still in the middle of the series.
I've tested this patch-set using updated LLVM version and have
a few notes:
- kernel/bpf/disasm.c needs an update to handle new instructions;
- test_verifier test 'invalid 64-bit BPF_END' from basic_instr.c
 is failing because '.code = BPF_ALU64 | BPF_END | BPF_TO_LE'
 is now valid;
- I've looked through the usage of BPF_LDX and found that there
 is a function seccomp.c:seccomp_check_filter(), that directly
 checks possible CLASS / CODE combinations. Should this function
 be updated to handle new instructions?

Thanks,
Eduard

> > 
> > To test this patch set, you need to have latest llvm from 'main' branch
> > of llvm-project repo and apply [2] on top of it.
> > 
> >   [1] https://lore.kernel.org/bpf/4bfe98be-5333-1c7e-2f6d-42486c8ec039@meta.com/
> >   [2] https://reviews.llvm.org/D144829
> > 
> > Changelogs:
> >   RFCv1 -> v2:
> >    . add more verifier supports for signed extend load and mov insns.
> >    . rename some insn names to be more consistent with intel practice.
> >    . add cpuv4 test runner for test progs.
> >    . add more unit and C tests.
> >    . add documentation.
> > 
> > Yonghong Song (15):
> >   bpf: Support new sign-extension load insns
> >   bpf: Fix sign-extension ctx member accesses
> >   bpf: Support new sign-extension mov insns
> >   bpf: Support new unconditional bswap instruction
> >   bpf: Support new signed div/mod instructions.
> >   bpf: Fix jit blinding with new sdiv/smov insns
> >   bpf: Support new 32bit offset jmp instruction
> >   selftests/bpf: Add a cpuv4 test runner for cpu=v4 testing
> >   selftests/bpf: Add unit tests for new sign-extension load insns
> >   selftests/bpf: Add unit tests for new sign-extension mov insns
> >   selftests/bpf: Add unit tests for new bswap insns
> >   selftests/bpf: Add unit tests for new sdiv/smod insns
> >   selftests/bpf: Add unit tests for new gotol insn
> >   selftests/bpf: Test ldsx with more complex cases
> >   docs/bpf: Add documentation for new instructions
> > 
> >  Documentation/bpf/bpf_design_QA.rst           |   5 -
> >  .../bpf/standardization/instruction-set.rst   | 100 ++-
> >  arch/x86/net/bpf_jit_comp.c                   | 131 ++-
> >  include/linux/filter.h                        |  14 +-
> >  include/uapi/linux/bpf.h                      |   1 +
> >  kernel/bpf/cgroup.c                           |  14 +-
> >  kernel/bpf/core.c                             | 174 +++-
> >  kernel/bpf/verifier.c                         | 315 ++++++--
> >  tools/include/uapi/linux/bpf.h                |   1 +
> >  tools/testing/selftests/bpf/.gitignore        |   2 +
> >  tools/testing/selftests/bpf/Makefile          |  18 +-
> >  .../selftests/bpf/bpf_testmod/bpf_testmod.c   |   9 +-
> >  .../selftests/bpf/prog_tests/test_ldsx_insn.c |  88 ++
> >  .../selftests/bpf/prog_tests/verifier.c       |  10 +
> >  .../selftests/bpf/progs/test_ldsx_insn.c      |  75 ++
> >  .../selftests/bpf/progs/verifier_bswap.c      |  45 ++
> >  .../selftests/bpf/progs/verifier_gotol.c      |  30 +
> >  .../selftests/bpf/progs/verifier_ldsx.c       | 115 +++
> >  .../selftests/bpf/progs/verifier_movsx.c      | 177 ++++
> >  .../selftests/bpf/progs/verifier_sdiv.c       | 763 ++++++++++++++++++
> >  20 files changed, 1929 insertions(+), 158 deletions(-)
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_ldsx_insn.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/test_ldsx_insn.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/verifier_bswap.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/verifier_gotol.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/verifier_ldsx.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/verifier_movsx.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/verifier_sdiv.c
> >