linux-kernel - [bpf-next 3/6] bpf,powerpc: Implement bpf_addr_space

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Message-ID: <20250805062747.3479221-4-skb99@linux.ibm.com>
Date: Tue,  5 Aug 2025 11:57:44 +0530
From: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
To: bpf@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: hbathini@...ux.ibm.com, sachinpb@...ux.ibm.com, venkat88@...ux.ibm.com,
        andrii@...nel.org, eddyz87@...il.com, mykolal@...com, ast@...nel.org,
        daniel@...earbox.net, martin.lau@...ux.dev, 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, memxor@...il.com,
        iii@...ux.ibm.com, shuah@...nel.org
Subject: [bpf-next 3/6] bpf,powerpc: Implement bpf_addr_space_cast instruction

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) : used to convert a bpf arena pointer to
a pointer in the userspace vma. This has to be converted by the JIT.

Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
---
 arch/powerpc/net/bpf_jit.h        |  1 +
 arch/powerpc/net/bpf_jit_comp.c   |  6 ++++++
 arch/powerpc/net/bpf_jit_comp64.c | 11 +++++++++++
 3 files changed, 18 insertions(+)

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 2d095a873305..748e30e8b5b4 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -165,6 +165,7 @@ struct codegen_context {
 	unsigned int exentry_idx;
 	unsigned int alt_exit_addr;
 	u64 arena_vm_start;
+	u64 user_vm_start;
 };
 
 #define bpf_to_ppc(r)	(ctx->b2p[r])
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 35bfdf4d8785..2b3f90930c27 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -205,6 +205,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	/* Make sure that the stack is quadword aligned. */
 	cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
 	cgctx.arena_vm_start = bpf_arena_get_kern_vm_start(fp->aux->arena);
+	cgctx.user_vm_start = bpf_arena_get_user_vm_start(fp->aux->arena);
 
 	/* Scouting faux-generate pass 0 */
 	if (bpf_jit_build_body(fp, NULL, NULL, &cgctx, addrs, 0, false)) {
@@ -441,6 +442,11 @@ bool bpf_jit_supports_kfunc_call(void)
 	return true;
 }
 
+bool bpf_jit_supports_arena(void)
+{
+	return IS_ENABLED(CONFIG_PPC64);
+}
+
 bool bpf_jit_supports_far_kfunc_call(void)
 {
 	return IS_ENABLED(CONFIG_PPC64);
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 16e62766c757..d4fe4dacf2d6 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -812,6 +812,17 @@ 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_cast_user(&insn[i])) {
+				EMIT(PPC_RAW_RLDICL(tmp1_reg, src_reg, 0, 32));
+				PPC_LI64(dst_reg, (ctx->user_vm_start & 0xffffffff00000000UL));
+				EMIT(PPC_RAW_CMPDI(tmp1_reg, 0));
+				PPC_BCC_SHORT(COND_EQ, (ctx->idx + 2) * 4);
+				EMIT(PPC_RAW_OR(tmp1_reg, dst_reg, tmp1_reg));
+				EMIT(PPC_RAW_MR(dst_reg, tmp1_reg));
+				break;
+			}
+
 			if (imm == 1) {
 				/* special mov32 for zext */
 				EMIT(PPC_RAW_RLWINM(dst_reg, dst_reg, 0, 0, 31));
-- 
2.43.5