Re: [PATCH bpf-next v2 02/11] LoongArch: BPF: Support internal-only MOV to resolve per-CPU addrs

[Tiezhu Yang]

On 2026/7/2 上午10:23, George Guo wrote:
> From: George Guo <guodongtai@xxxxxxxxxx>
>
> Support the internal-only BPF_MOV instruction that resolves the absolute
> address of per-CPU data from its per-CPU offset. This instruction is used
> only for internal inlining optimizations between the BPF verifier and the
> JITs (e.g. inlining bpf_get_smp_processor_id() and per-CPU map lookups).
>
> LoongArch keeps the per-CPU offset of the current CPU in $r21
> (__my_cpu_offset), so resolving a per-CPU address only requires adding
> $r21 to the source register holding the per-CPU offset. Advertise the
> capability via bpf_jit_supports_percpu_insn().
>
> Signed-off-by: George Guo <guodongtai@xxxxxxxxxx>
> ---
>   arch/loongarch/include/asm/inst.h |  1 +
>   arch/loongarch/net/bpf_jit.c      | 14 ++++++++++++++
>   2 files changed, 15 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index 76b723590023..44fb5ad26d1a 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -404,6 +404,7 @@ enum loongarch_gpr {
>   	LOONGARCH_GPR_T6,
>   	LOONGARCH_GPR_T7,
>   	LOONGARCH_GPR_T8,
> +	LOONGARCH_GPR_U0 = 21,	/* Kernel per-CPU base register ($r21) */
>   	LOONGARCH_GPR_FP = 22,
>   	LOONGARCH_GPR_S0 = 23,
>   	LOONGARCH_GPR_S1,
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index 5e34e9e3f508..b4208fa3a242 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -759,6 +759,15 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
>   			move_reg(ctx, dst, t1);
>   			break;
>   		}
> +		if (insn_is_mov_percpu_addr(insn)) {
> +			if (dst != src)
> +				move_reg(ctx, dst, src);
> +#ifdef CONFIG_SMP
> +			/* dst += __my_cpu_offset, held in $r21 */
> +			emit_insn(ctx, addd, dst, dst, LOONGARCH_GPR_U0);
> +#endif

How to test? Did you test under !CONFIG_SMP?

Thanks,
Tiezhu