On 03/29, Andrii Nakryiko wrote:
> Add BPF instructions for working with per-CPU data. These instructions
> are internal-only and users are not allowed to use them directly. They
> will only be used for internal inlining optimizations for now.
>
> Two different instructions are added. One, with BPF_MEM_PERCPU opcode,
> performs memory dereferencing of a per-CPU "address" (which is actually
> an offset). This one is useful when inlined logic needs to load data
> stored in per-CPU storage (bpf_get_smp_processor_id() is one such
> example).
>
> Another, with BPF_ADDR_PERCPU opcode, performs a resolution of a per-CPU
> address (offset) stored in a register. This one is useful anywhere where
> per-CPU data is not read, but rather is returned to user as just
> absolute raw memory pointer (useful in bpf_map_lookup_elem() helper
> inlinings, for example).
>
> 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@xxxxxxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 29 +++++++++++++++++++++++++++++
> include/linux/filter.h | 27 +++++++++++++++++++++++++++
> kernel/bpf/core.c | 5 +++++
> kernel/bpf/disasm.c | 33 ++++++++++++++++++++++++++-------
> 4 files changed, 87 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 3b639d6f2f54..610bbedaae70 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -1910,6 +1910,30 @@ st: if (is_imm8(insn->off))
> }
> break;
>
> + /* internal-only per-cpu zero-extending memory load */
> + case BPF_LDX | BPF_MEM_PERCPU | BPF_B:
> + case BPF_LDX | BPF_MEM_PERCPU | BPF_H:
> + case BPF_LDX | BPF_MEM_PERCPU | BPF_W:
> + case BPF_LDX | BPF_MEM_PERCPU | BPF_DW:
> + insn_off = insn->off;
> + EMIT1(0x65); /* gs segment modifier */
> + emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn_off);
> + break;
> +
> + /* internal-only load-effective-address-of per-cpu offset */
> + case BPF_LDX | BPF_ADDR_PERCPU | BPF_DW: {
> + u32 off = (u32)(void *)&this_cpu_off;
> +
> + /* mov <dst>, <src> (if necessary) */
> + EMIT_mov(dst_reg, src_reg);
> +
> + /* add <dst>, gs:[<off>] */
> + EMIT2(0x65, add_1mod(0x48, dst_reg));
> + EMIT3(0x03, add_1reg(0x04, dst_reg), 0x25);
> + EMIT(off, 4);
> +
> + break;
> + }
> case BPF_STX | BPF_ATOMIC | BPF_W:
> case BPF_STX | BPF_ATOMIC | BPF_DW:
> if (insn->imm == (BPF_AND | BPF_FETCH) ||
> @@ -3365,6 +3389,11 @@ bool bpf_jit_supports_subprog_tailcalls(void)
> return true;
> }
>
> +bool bpf_jit_supports_percpu_insns(void)
> +{
> + return true;
> +}
> +
> void bpf_jit_free(struct bpf_prog *prog)
> {
> if (prog->jited) {
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 44934b968b57..85ffaa238bc1 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -75,6 +75,14 @@ struct ctl_table_header;
> /* unused opcode to mark special load instruction. Same as BPF_MSH */
> #define BPF_PROBE_MEM32 0xa0
>
> +/* unused opcode to mark special zero-extending per-cpu load instruction. */
> +#define BPF_MEM_PERCPU 0xc0
> +
> +/* unused opcode to mark special load-effective-address-of instruction for
> + * a given per-CPU offset
> + */
> +#define BPF_ADDR_PERCPU 0xe0
> +
> /* unused opcode to mark call to interpreter with arguments */
> #define BPF_CALL_ARGS 0xe0
>
> @@ -318,6 +326,24 @@ static inline bool insn_is_cast_user(const struct bpf_insn *insn)
> .off = OFF, \
> .imm = 0 })
>
> +/* Per-CPU zero-extending memory load (internal-only) */
> +#define BPF_LDX_MEM_PERCPU(SIZE, DST, SRC, OFF) \
> + ((struct bpf_insn) { \
> + .code = BPF_LDX | BPF_SIZE(SIZE) | BPF_MEM_PERCPU,\
> + .dst_reg = DST, \
> + .src_reg = SRC, \
> + .off = OFF, \
> + .imm = 0 })
> +
[..]
> +/* Load effective address of a given per-CPU offset */
nit: mark this one as internal only as well in the comment?
(the change overall looks awesome, looking forward to trying it out)
