linux-kernel - [PATCH v1 06/10] powerpc/bpf: Perform complete extra passes to update addresses

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Message-Id: <c13ebeb4d5d169bda6d1d60ccaa6cc956308308d.1669881248.git.christophe.leroy@csgroup.eu>
Date:   Thu,  1 Dec 2022 08:56:31 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        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>
Subject: [PATCH v1 06/10] powerpc/bpf: Perform complete extra passes to update addresses

BPF core calls the jit compiler again for an extra pass in order
to properly set subprog addresses.

Unlike other architectures, powerpc only updates the addresses
during that extra pass. It means that holes must have been left
in the code in order to enable the maximum possible instruction
size.

In order avoid waste of space, and waste of CPU time on powerpc
processors on which the NOP instruction is not 0-cycle, perform
two real additional passes.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/net/bpf_jit_comp.c | 85 ---------------------------------
 1 file changed, 85 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 43e634126514..8833bf23f5aa 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -23,74 +23,6 @@ static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
 	memset32(area, BREAKPOINT_INSTRUCTION, size / 4);
 }
 
-/* Fix updated addresses (for subprog calls, ldimm64, et al) during extra pass */
-static int bpf_jit_fixup_addresses(struct bpf_prog *fp, u32 *image,
-				   struct codegen_context *ctx, u32 *addrs)
-{
-	const struct bpf_insn *insn = fp->insnsi;
-	bool func_addr_fixed;
-	u64 func_addr;
-	u32 tmp_idx;
-	int i, j, ret;
-
-	for (i = 0; i < fp->len; i++) {
-		/*
-		 * During the extra pass, only the branch target addresses for
-		 * the subprog calls need to be fixed. All other instructions
-		 * can left untouched.
-		 *
-		 * The JITed image length does not change because we already
-		 * ensure that the JITed instruction sequence for these calls
-		 * are of fixed length by padding them with NOPs.
-		 */
-		if (insn[i].code == (BPF_JMP | BPF_CALL) &&
-		    insn[i].src_reg == BPF_PSEUDO_CALL) {
-			ret = bpf_jit_get_func_addr(fp, &insn[i], true,
-						    &func_addr,
-						    &func_addr_fixed);
-			if (ret < 0)
-				return ret;
-
-			/*
-			 * Save ctx->idx as this would currently point to the
-			 * end of the JITed image and set it to the offset of
-			 * the instruction sequence corresponding to the
-			 * subprog call temporarily.
-			 */
-			tmp_idx = ctx->idx;
-			ctx->idx = addrs[i] / 4;
-			ret = bpf_jit_emit_func_call_rel(image, ctx, func_addr);
-			if (ret)
-				return ret;
-
-			/*
-			 * Restore ctx->idx here. This is safe as the length
-			 * of the JITed sequence remains unchanged.
-			 */
-			ctx->idx = tmp_idx;
-		} else if (insn[i].code == (BPF_LD | BPF_IMM | BPF_DW)) {
-			tmp_idx = ctx->idx;
-			ctx->idx = addrs[i] / 4;
-#ifdef CONFIG_PPC32
-			PPC_LI32(bpf_to_ppc(insn[i].dst_reg) - 1, (u32)insn[i + 1].imm);
-			PPC_LI32(bpf_to_ppc(insn[i].dst_reg), (u32)insn[i].imm);
-			for (j = ctx->idx - addrs[i] / 4; j < 4; j++)
-				EMIT(PPC_RAW_NOP());
-#else
-			func_addr = ((u64)(u32)insn[i].imm) | (((u64)(u32)insn[i + 1].imm) << 32);
-			PPC_LI64(bpf_to_ppc(insn[i].dst_reg), func_addr);
-			/* overwrite rest with nops */
-			for (j = ctx->idx - addrs[i] / 4; j < 5; j++)
-				EMIT(PPC_RAW_NOP());
-#endif
-			ctx->idx = tmp_idx;
-			i++;
-		}
-	}
-
-	return 0;
-}
-
 int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, long exit_addr)
 {
 	if (!exit_addr || is_offset_in_branch_range(exit_addr - (ctx->idx * 4))) {
@@ -234,22 +166,6 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 skip_init_ctx:
 	code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
 
-	if (extra_pass) {
-		/*
-		 * Do not touch the prologue and epilogue as they will remain
-		 * unchanged. Only fix the branch target address for subprog
-		 * calls in the body, and ldimm64 instructions.
-		 *
-		 * This does not change the offsets and lengths of the subprog
-		 * call instruction sequences and hence, the size of the JITed
-		 * image as well.
-		 */
-		bpf_jit_fixup_addresses(fp, code_base, &cgctx, addrs);
-
-		/* There is no need to perform the usual passes. */
-		goto skip_codegen_passes;
-	}
-
 	/* Code generation passes 1-2 */
 	for (pass = 1; pass < 3; pass++) {
 		/* Now build the prologue, body code & epilogue for real. */
@@ -268,7 +184,6 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 				proglen - (cgctx.idx * 4), cgctx.seen);
 	}
 
-skip_codegen_passes:
 	if (bpf_jit_enable > 1)
 		/*
 		 * Note that we output the base address of the code_base
-- 
2.38.1