linux-kernel - [PATCH 1/2] powerpc, bpf: Support internal-only MOV instruction to resolve per-CPU addrs

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Message-ID: <20250311160955.825647-2-skb99@linux.ibm.com>
Date: Tue, 11 Mar 2025 21:39:54 +0530
From: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
To: bpf@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Cc: ast@...nel.org, hbathini@...ux.ibm.com, andrii@...nel.org,
        daniel@...earbox.net, martin.lau@...ux.dev, eddyz87@...il.com,
        song@...nel.org, yonghong.song@...ux.dev, john.fastabend@...il.com,
        kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com,
        jolsa@...nel.org, christophe.leroy@...roup.eu, naveen@...nel.org,
        maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com
Subject: [PATCH 1/2] powerpc, bpf: Support internal-only MOV instruction to resolve per-CPU addrs

With the introduction of commit 7bdbf7446305 ("bpf: add special
internal-only MOV instruction to resolve per-CPU addrs"),
a new BPF instruction BPF_MOV64_PERCPU_REG has been added to
resolve absolute addresses of per-CPU data from their per-CPU
offsets. This update requires enabling support for this
instruction in the powerpc JIT compiler.

As of commit 7a0268fa1a36 ("[PATCH] powerpc/64: per cpu data
optimisations"), the per-CPU data offset for the CPU is stored in
the paca.

To support this BPF instruction in the powerpc JIT, the following
powerpc instructions are emitted:

mr dst_reg, src_reg		//Move src_reg to dst_reg, if src_reg != dst_reg
ld tmp1_reg, 48(13)		//Load per-CPU data offset from paca(r13) in tmp1_reg.
add dst_reg, dst_reg, tmp1_reg	//Add the per cpu offset to the dst.

To evaluate the performance improvements introduced by this change,
the benchmark described in [1] was employed.

Before Change:
glob-arr-inc   :   41.580 ± 0.034M/s
arr-inc        :   39.592 ± 0.055M/s
hash-inc       :   25.873 ± 0.012M/s

After Change:
glob-arr-inc   :   42.024 ± 0.049M/s
arr-inc        :   55.447 ± 0.031M/s
hash-inc       :   26.565 ± 0.014M/s

[1] https://github.com/anakryiko/linux/commit/8dec900975ef

Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
---
 arch/powerpc/net/bpf_jit_comp.c   | 5 +++++
 arch/powerpc/net/bpf_jit_comp64.c | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 2991bb171a9b..3d4bd45a9a22 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -440,6 +440,11 @@ bool bpf_jit_supports_far_kfunc_call(void)
 	return IS_ENABLED(CONFIG_PPC64);
 }
 
+bool bpf_jit_supports_percpu_insn(void)
+{
+	return true;
+}
+
 void *arch_alloc_bpf_trampoline(unsigned int size)
 {
 	return bpf_prog_pack_alloc(size, bpf_jit_fill_ill_insns);
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 233703b06d7c..06f06770ceea 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -679,6 +679,14 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		 */
 		case BPF_ALU | BPF_MOV | BPF_X: /* (u32) dst = src */
 		case BPF_ALU64 | BPF_MOV | BPF_X: /* dst = src */
+			if (insn_is_mov_percpu_addr(&insn[i])) {
+				if (dst_reg != src_reg)
+					EMIT(PPC_RAW_MR(dst_reg, src_reg));
+#ifdef CONFIG_SMP
+				EMIT(PPC_RAW_LD(tmp1_reg, _R13, offsetof(struct paca_struct, data_offset)));
+				EMIT(PPC_RAW_ADD(dst_reg, dst_reg, tmp1_reg));
+#endif
+			}
 			if (imm == 1) {
 				/* special mov32 for zext */
 				EMIT(PPC_RAW_RLWINM(dst_reg, dst_reg, 0, 0, 31));
-- 
2.43.5