linux-kernel - Re: [PATCH bpf-next v3 2/2] bpf,riscv: Implement bpf_addr_space

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Date: Wed, 27 Mar 2024 15:28:43 +0800
From: Pu Lehui <pulehui@...weicloud.com>
To: Puranjay Mohan <puranjay12@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Björn Töpel
 <bjorn@...nel.org>, Luke Nelson <luke.r.nels@...il.com>,
 Xi Wang <xi.wang@...il.com>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 2/2] bpf,riscv: Implement bpf_addr_space_cast
 instruction


On 2024/3/27 6:49, Puranjay Mohan wrote:
> LLVM generates bpf_addr_space_cast instruction while translating
> pointers between native (zero) address space and
> __attribute__((address_space(N))). The addr_space=0 is reserved as
> bpf_arena address space.
> 
> rY = addr_space_cast(rX, 0, 1) is processed by the verifier and
> converted to normal 32-bit move: wX = wY
> 
> rY = addr_space_cast(rX, 1, 0) has to be converted by JIT.
> 
> Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
> ---
>   arch/riscv/net/bpf_jit.h        |  1 +
>   arch/riscv/net/bpf_jit_comp64.c | 14 ++++++++++++++
>   arch/riscv/net/bpf_jit_core.c   |  1 +
>   3 files changed, 16 insertions(+)
> 
> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
> index 8a47da08dd9c..5fc374ed98ea 100644
> --- a/arch/riscv/net/bpf_jit.h
> +++ b/arch/riscv/net/bpf_jit.h
> @@ -82,6 +82,7 @@ struct rv_jit_context {
>   	unsigned long flags;
>   	int stack_size;
>   	u64 arena_vm_start;
> +	u64 user_vm_start;
>   };
>   
>   /* Convert from ninsns to bytes. */
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 73726f455f6b..77ea306452d4 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -1081,6 +1081,15 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>   	/* dst = src */
>   	case BPF_ALU | BPF_MOV | BPF_X:
>   	case BPF_ALU64 | BPF_MOV | BPF_X:
> +		if (insn_is_cast_user(insn)) {
> +			emit_mv(RV_REG_T1, rs, ctx);
> +			emit_zextw(RV_REG_T1, RV_REG_T1, ctx);
> +			emit_imm(rd, (ctx->user_vm_start >> 32) << 32, ctx);
> +			emit(rv_beq(RV_REG_T1, RV_REG_ZERO, 4), ctx);
> +			emit_or(RV_REG_T1, rd, RV_REG_T1, ctx);
> +			emit_mv(rd, RV_REG_T1, ctx);
> +			break;
> +		}
>   		if (imm == 1) {
>   			/* Special mov32 for zext */
>   			emit_zextw(rd, rd, ctx);
> @@ -2026,3 +2035,8 @@ bool bpf_jit_supports_ptr_xchg(void)
>   {
>   	return true;
>   }
> +
> +bool bpf_jit_supports_arena(void)
> +{
> +	return true;
> +}
> diff --git a/arch/riscv/net/bpf_jit_core.c b/arch/riscv/net/bpf_jit_core.c
> index 9ab739b9f9a2..8a69d6d81e32 100644
> --- a/arch/riscv/net/bpf_jit_core.c
> +++ b/arch/riscv/net/bpf_jit_core.c
> @@ -81,6 +81,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
>   	}
>   
>   	ctx->arena_vm_start = bpf_arena_get_kern_vm_start(prog->aux->arena);
> +	ctx->user_vm_start = bpf_arena_get_user_vm_start(prog->aux->arena);
>   	ctx->prog = prog;
>   	ctx->offset = kcalloc(prog->len, sizeof(int), GFP_KERNEL);
>   	if (!ctx->offset) {

Reviewed-by: Pu Lehui <pulehui@...wei.com>
Tested-by: Pu Lehui <pulehui@...wei.com>