RE: [PATCH v2 bpf-next 1/4] bpf: add special internal-only MOV instruction to resolve per-CPU addrs

[John Fastabend <john.fastabend@gmail.com>]

Andrii Nakryiko wrote:
> Add a new BPF instruction for resolving absolute addresses of per-CPU
> data from their per-CPU offsets. This instruction is internal-only and
> users are not allowed to use them directly. They will only be used for
> internal inlining optimizations for now between BPF verifier and BPF JITs.
> 
> We use a special BPF_MOV | BPF_ALU64 | BPF_X form with insn->off field
> set to BPF_ADDR_PERCPU = -1. I used negative offset value to distinguish
> them from positive ones used by user-exposed instructions.
> 
> Such instruction performs a resolution of a per-CPU offset stored in
> a register to a valid kernel address which can be dereferenced. It is
> useful in any use case where absolute address of a per-CPU data has to
> be resolved (e.g., in inlining bpf_map_lookup_elem()).
> 
> BPF disassembler is also taught to recognize them to support dumping
> final BPF assembly code (non-JIT'ed version).
> 
> Add arch-specific way for BPF JITs to mark support for this instructions.
> 
> This patch also adds support for these instructions in x86-64 BPF JIT.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  arch/x86/net/bpf_jit_comp.c | 16 ++++++++++++++++
>  include/linux/filter.h      | 20 ++++++++++++++++++++
>  kernel/bpf/core.c           |  5 +++++
>  kernel/bpf/disasm.c         | 14 ++++++++++++++
>  4 files changed, 55 insertions(+)

LGTM

Acked-by: John Fastabend <john.fastabend@gmail.com>