Merge branch 'mixing-bpf2bpf-and-tailcalls-for-rv64'

Pu Lehui says:

====================
Mixing bpf2bpf and tailcalls for RV64

In the current RV64 JIT, if we just don't initialize the TCC in subprog,
the TCC can be propagated from the parent process to the subprocess, but
the updated TCC of the parent process cannot be restored when the
subprocess exits. Since the RV64 TCC is initialized before saving the
callee saved registers into the stack, we cannot use the callee saved
register to pass the TCC, otherwise the original value of the callee
saved register will be destroyed. So we implemented mixing bpf2bpf and
tailcalls similar to x86_64, i.e. using a non-callee saved register to
transfer the TCC between functions, and saving that register to the
stack to protect the TCC value. As for the tailcall hierarchy issue,
inspired by the s390's low-overhead approach, we store TCC from
RV_REG_TCC back to stack after calling bpf2bpf call or calling orig bpf
func in bpf trampoline.

In addition, some code cleans are also attached to this patchset.

Tests test_bpf.ko and test_verifier have passed, as well as the relative
testcases of test_progs*.

v6:
- Add new patch to fix memory leak in bpf_jit_free. (Sashiko)

v5: https://lore.kernel.org/bpf/20260707142219.2871758-1-pulehui@huaweicloud.com
- Fix TCC value was not restored to RV_REG_TCC upon trampoline exit,
  resulting in an infinite tail call. (Sashiko)
- Fix epilogue not restored TCC value to RV_REG_TCC, resulting in
  leaf tailcall callee may clobbered RV_REG_TCC. (Sashiko)
- Remove patch of `Remove ctx->offset initialization` as it would hit
  some corner case. (Sashiko)
- Fix double-count kcfi insn when tailcall to target. (Sashiko)
- Add detail for selftest commit message. (BPF BOT)

v4: https://lore.kernel.org/bpf/20260629140048.733346-1-pulehui@huaweicloud.com
- Fix tailcall hierarchy issue.
- use is_struct_ops_tramp helper in bpf trampoline

v3: https://lore.kernel.org/bpf/20240201083351.943121-1-pulehui@huaweicloud.com
- Remove duplicate RV_REG_TCC load in epiloguei. (Björn Töpel)

v2: https://lore.kernel.org/bpf/20240130040958.230673-1-pulehui@huaweicloud.com
- Fix emit restore RV_REG_TCC double times when `flags &
  BPF_TRAMP_F_CALL_ORIG`
- Use bpf_is_subprog helper

v1: https://lore.kernel.org/bpf/20230919035711.3297256-1-pulehui@huaweicloud.com
====================

Link: https://patch.msgid.link/20260708064436.2971933-1-pulehui@huaweicloud.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

arch/arm64/net/bpf_jit_comp.c

@@ -2557,12 +2557,6 @@ static void restore_args(struct jit_ctx *ctx, int bargs_off, int nregs)
 	}
 }
 
-static bool is_struct_ops_tramp(const struct bpf_tramp_nodes *fentry_nodes)
-{
-	return fentry_nodes->nr_nodes == 1 &&
-		fentry_nodes->nodes[0]->link->type == BPF_LINK_TYPE_STRUCT_OPS;
-}
-
 static void store_func_meta(struct jit_ctx *ctx, u64 func_meta, int func_meta_off)
 {
 	emit_a64_mov_i64(A64_R(10), func_meta, ctx);

arch/riscv/net/bpf_jit.h

@@ -81,6 +81,7 @@ struct rv_jit_context {
 	int ex_jmp_off;
 	unsigned long flags;
 	int stack_size;
+	int tcc_offset;
 	u64 arena_vm_start;
 	u64 user_vm_start;
 };

arch/riscv/net/bpf_jit_comp64.c

@@ -18,12 +18,12 @@
 #define RV_MAX_REG_ARGS 8
 #define RV_FENTRY_NINSNS 2
 #define RV_FENTRY_NBYTES (RV_FENTRY_NINSNS * 4)
-#define RV_KCFI_NINSNS (IS_ENABLED(CONFIG_CFI) ? 1 : 0)
 /* imm that allows emit_imm to emit max count insns */
 #define RV_MAX_COUNT_IMM 0x7FFF7FF7FF7FF7FF
+/* fentry and TCC init insns will be skipped on tailcall */
+#define RV_TAILCALL_OFFSET ((RV_FENTRY_NINSNS + 1) * 4)
 
 #define RV_REG_TCC RV_REG_A6
-#define RV_REG_TCC_SAVED RV_REG_S6 /* Store A6 in S6 if program do calls */
 #define RV_REG_ARENA RV_REG_S7 /* For storing arena_vm_start */
 
 static const int regmap[] = {
@@ -57,14 +57,12 @@ static const int pt_regmap[] = {
 };
 
 enum {
-	RV_CTX_F_SEEN_TAIL_CALL =	0,
 	RV_CTX_F_SEEN_CALL =		RV_REG_RA,
 	RV_CTX_F_SEEN_S1 =		RV_REG_S1,
 	RV_CTX_F_SEEN_S2 =		RV_REG_S2,
 	RV_CTX_F_SEEN_S3 =		RV_REG_S3,
 	RV_CTX_F_SEEN_S4 =		RV_REG_S4,
 	RV_CTX_F_SEEN_S5 =		RV_REG_S5,
-	RV_CTX_F_SEEN_S6 =		RV_REG_S6,
 };
 
 static u8 bpf_to_rv_reg(int bpf_reg, struct rv_jit_context *ctx)
@@ -77,7 +75,6 @@ static u8 bpf_to_rv_reg(int bpf_reg, struct rv_jit_context *ctx)
 	case RV_CTX_F_SEEN_S3:
 	case RV_CTX_F_SEEN_S4:
 	case RV_CTX_F_SEEN_S5:
-	case RV_CTX_F_SEEN_S6:
 		__set_bit(reg, &ctx->flags);
 	}
 	return reg;
@@ -92,7 +89,6 @@ static bool seen_reg(int reg, struct rv_jit_context *ctx)
 	case RV_CTX_F_SEEN_S3:
 	case RV_CTX_F_SEEN_S4:
 	case RV_CTX_F_SEEN_S5:
-	case RV_CTX_F_SEEN_S6:
 		return test_bit(reg, &ctx->flags);
 	}
 	return false;
@@ -108,32 +104,6 @@ static void mark_call(struct rv_jit_context *ctx)
 	__set_bit(RV_CTX_F_SEEN_CALL, &ctx->flags);
 }
 
-static bool seen_call(struct rv_jit_context *ctx)
-{
-	return test_bit(RV_CTX_F_SEEN_CALL, &ctx->flags);
-}
-
-static void mark_tail_call(struct rv_jit_context *ctx)
-{
-	__set_bit(RV_CTX_F_SEEN_TAIL_CALL, &ctx->flags);
-}
-
-static bool seen_tail_call(struct rv_jit_context *ctx)
-{
-	return test_bit(RV_CTX_F_SEEN_TAIL_CALL, &ctx->flags);
-}
-
-static u8 rv_tail_call_reg(struct rv_jit_context *ctx)
-{
-	mark_tail_call(ctx);
-
-	if (seen_call(ctx)) {
-		__set_bit(RV_CTX_F_SEEN_S6, &ctx->flags);
-		return RV_REG_S6;
-	}
-	return RV_REG_A6;
-}
-
 static bool is_32b_int(s64 val)
 {
 	return -(1L << 31) <= val && val < (1L << 31);
@@ -258,23 +228,20 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
 		emit_ld(RV_REG_S5, store_offset, RV_REG_SP, ctx);
 		store_offset -= 8;
 	}
-	if (seen_reg(RV_REG_S6, ctx)) {
-		emit_ld(RV_REG_S6, store_offset, RV_REG_SP, ctx);
-		store_offset -= 8;
-	}
 	if (ctx->arena_vm_start) {
 		emit_ld(RV_REG_ARENA, store_offset, RV_REG_SP, ctx);
 		store_offset -= 8;
 	}
 
+	/* restore TCC from stack to RV_REG_TCC */
+	emit_ld(RV_REG_TCC, ctx->tcc_offset, RV_REG_SP, ctx);
+
 	emit_addi(RV_REG_SP, RV_REG_SP, stack_adjust, ctx);
 	/* Set return value. */
 	if (!is_tail_call)
 		emit_addiw(RV_REG_A0, RV_REG_A5, 0, ctx);
 	emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
-		  /* kcfi, fentry and TCC init insns will be skipped on tailcall */
-		  is_tail_call ? (RV_KCFI_NINSNS + RV_FENTRY_NINSNS + 1) * 4 : 0,
-		  ctx);
+		  is_tail_call ? RV_TAILCALL_OFFSET : 0, ctx);
 }
 
 static void emit_bcc(u8 cond, u8 rd, u8 rs, int rvoff,
@@ -355,7 +322,6 @@ static void emit_branch(u8 cond, u8 rd, u8 rs, int rvoff,
 static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 {
 	int tc_ninsn, off, start_insn = ctx->ninsns;
-	u8 tcc = rv_tail_call_reg(ctx);
 
 	/* a0: &ctx
 	 * a1: &array
@@ -378,7 +344,8 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 	/* if (--TCC < 0)
 	 *     goto out;
 	 */
-	emit_addi(RV_REG_TCC, tcc, -1, ctx);
+	emit_ld(RV_REG_TCC, ctx->tcc_offset, RV_REG_SP, ctx);
+	emit_addi(RV_REG_TCC, RV_REG_TCC, -1, ctx);
 	off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
 	emit_branch(BPF_JSLT, RV_REG_TCC, RV_REG_ZERO, off, ctx);
 
@@ -394,7 +361,10 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
 	off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
 	emit_branch(BPF_JEQ, RV_REG_T2, RV_REG_ZERO, off, ctx);
 
-	/* goto *(prog->bpf_func + 4); */
+	/* store updated TCC back to stack */
+	emit_sd(RV_REG_SP, ctx->tcc_offset, RV_REG_TCC, ctx);
+
+	/* goto *(prog->bpf_func + RV_TAILCALL_OFFSET); */
 	off = offsetof(struct bpf_prog, bpf_func);
 	if (is_12b_check(off, insn))
 		return -1;
@@ -1028,12 +998,13 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 	int i, ret, offset;
 	int *branches_off = NULL;
 	int stack_size = 0, nr_arg_slots = 0;
-	int retval_off, args_off, func_meta_off, ip_off, run_ctx_off, sreg_off, stk_arg_off;
+	int retval_off, args_off, func_meta_off, ip_off;
+	int run_ctx_off, sreg_off, stk_arg_off, tcc_off;
 	int cookie_off, cookie_cnt;
 	struct bpf_tramp_nodes *fentry = &tnodes[BPF_TRAMP_FENTRY];
 	struct bpf_tramp_nodes *fexit = &tnodes[BPF_TRAMP_FEXIT];
 	struct bpf_tramp_nodes *fmod_ret = &tnodes[BPF_TRAMP_MODIFY_RETURN];
-	bool is_struct_ops = flags & BPF_TRAMP_F_INDIRECT;
+	bool is_struct_ops = is_struct_ops_tramp(fentry);
 	void *orig_call = func_addr;
 	bool save_ret;
 	u64 func_meta;
@@ -1079,6 +1050,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 	 *
 	 * FP - sreg_off    [ callee saved reg	]
 	 *
+	 * FP - tcc_off     [ tail call count	] BPF_TRAMP_F_TAIL_CALL_CTX
+	 *
 	 *		    [ pads              ] pads for 16 bytes alignment
 	 *
 	 *		    [ stack_argN        ]
@@ -1126,6 +1099,11 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 	stack_size += 8;
 	sreg_off = stack_size;
 
+	if (flags & BPF_TRAMP_F_TAIL_CALL_CTX) {
+		stack_size += 8;
+		tcc_off = stack_size;
+	}
+
 	if ((flags & BPF_TRAMP_F_CALL_ORIG) && (nr_arg_slots - RV_MAX_REG_ARGS > 0))
 		stack_size += (nr_arg_slots - RV_MAX_REG_ARGS) * 8;
 
@@ -1160,6 +1138,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 		emit_addi(RV_REG_FP, RV_REG_SP, stack_size, ctx);
 	}
 
+	/* store tail call count */
+	if (flags & BPF_TRAMP_F_TAIL_CALL_CTX)
+		emit_sd(RV_REG_FP, -tcc_off, RV_REG_TCC, ctx);
+
 	/* callee saved register S1 to pass start time */
 	emit_sd(RV_REG_FP, -sreg_off, RV_REG_S1, ctx);
 
@@ -1195,7 +1177,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 	}
 
 	if (fmod_ret->nr_nodes) {
-		branches_off = kzalloc_objs(int, fmod_ret->nr_nodes);
+		branches_off = kvzalloc_objs(int, fmod_ret->nr_nodes);
 		if (!branches_off)
 			return -ENOMEM;
 
@@ -1218,9 +1200,15 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 		orig_call += RV_FENTRY_NINSNS * 4;
 		restore_args(min_t(int, nr_arg_slots, RV_MAX_REG_ARGS), args_off, ctx);
 		restore_stack_args(nr_arg_slots - RV_MAX_REG_ARGS, args_off, stk_arg_off, ctx);
+		/* restore TCC to RV_REG_TCC before calling the orig bpf func */
+		if (flags & BPF_TRAMP_F_TAIL_CALL_CTX)
+			emit_ld(RV_REG_TCC, -tcc_off, RV_REG_FP, ctx);
 		ret = emit_call((const u64)orig_call, true, ctx);
 		if (ret)
 			goto out;
+		/* store updated TCC back to stack after calling the orig bpf func */
+		if (flags & BPF_TRAMP_F_TAIL_CALL_CTX)
+			emit_sd(RV_REG_FP, -tcc_off, RV_REG_TCC, ctx);
 		emit_sd(RV_REG_FP, -retval_off, RV_REG_A0, ctx);
 		emit_sd(RV_REG_FP, -(retval_off - 8), regmap[BPF_REG_0], ctx);
 		im->ip_after_call = ctx->ro_insns + ctx->ninsns;
@@ -1273,6 +1261,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 
 	emit_ld(RV_REG_S1, -sreg_off, RV_REG_FP, ctx);
 
+	/* restore TCC from stack to RV_REG_TCC */
+	if (flags & BPF_TRAMP_F_TAIL_CALL_CTX)
+		emit_ld(RV_REG_TCC, -tcc_off, RV_REG_FP, ctx);
+
 	if (!is_struct_ops) {
 		/* trampoline called from function entry */
 		emit_ld(RV_REG_T0, stack_size - 8, RV_REG_SP, ctx);
@@ -1300,7 +1292,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 
 	ret = ctx->ninsns;
 out:
-	kfree(branches_off);
+	kvfree(branches_off);
 	return ret;
 }
 
@@ -1837,10 +1829,18 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 			}
 		}
 
+		/* restore TCC to RV_REG_TCC before bpf2bpf call */
+		if (aux->tail_call_reachable && insn->src_reg == BPF_PSEUDO_CALL)
+			emit_ld(RV_REG_TCC, ctx->tcc_offset, RV_REG_SP, ctx);
+
 		ret = emit_call(addr, fixed_addr, ctx);
 		if (ret)
 			return ret;
 
+		/* store updated TCC back to stack after bpf2bpf call */
+		if (aux->tail_call_reachable && insn->src_reg == BPF_PSEUDO_CALL)
+			emit_sd(RV_REG_SP, ctx->tcc_offset, RV_REG_TCC, ctx);
+
 		if (insn->src_reg != BPF_PSEUDO_CALL)
 			emit_mv(bpf_to_rv_reg(BPF_REG_0, ctx), RV_REG_A0, ctx);
 		break;
@@ -2020,10 +2020,9 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
 		stack_adjust += 8;
 	if (seen_reg(RV_REG_S5, ctx))
 		stack_adjust += 8;
-	if (seen_reg(RV_REG_S6, ctx))
-		stack_adjust += 8;
 	if (ctx->arena_vm_start)
 		stack_adjust += 8;
+	stack_adjust += 8; /* RV_REG_TCC */
 
 	stack_adjust = round_up(stack_adjust, STACK_ALIGN);
 	stack_adjust += bpf_stack_adjust;
@@ -2033,15 +2032,16 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
 	/* emit kcfi type preamble immediately before the  first insn */
 	emit_kcfi(is_subprog ? cfi_bpf_subprog_hash : cfi_bpf_hash, ctx);
 
+	/* bpf prog starts here as kcfi skipped during prog->bpf_func setup */
+
 	/* nops reserved for auipc+jalr pair */
 	for (i = 0; i < RV_FENTRY_NINSNS; i++)
 		emit(rv_nop(), ctx);
 
-	/* First instruction is always setting the tail-call-counter
-	 * (TCC) register. This instruction is skipped for tail calls.
-	 * Force using a 4-byte (non-compressed) instruction.
-	 */
-	emit(rv_addi(RV_REG_TCC, RV_REG_ZERO, MAX_TAIL_CALL_CNT), ctx);
+	if (!is_subprog)
+		emit(rv_addi(RV_REG_TCC, RV_REG_ZERO, MAX_TAIL_CALL_CNT), ctx);
+
+	/* tailcall starts here, emit insn before it must be fixed */
 
 	emit_addi(RV_REG_SP, RV_REG_SP, -stack_adjust, ctx);
 
@@ -2071,26 +2071,20 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
 		emit_sd(RV_REG_SP, store_offset, RV_REG_S5, ctx);
 		store_offset -= 8;
 	}
-	if (seen_reg(RV_REG_S6, ctx)) {
-		emit_sd(RV_REG_SP, store_offset, RV_REG_S6, ctx);
-		store_offset -= 8;
-	}
 	if (ctx->arena_vm_start) {
 		emit_sd(RV_REG_SP, store_offset, RV_REG_ARENA, ctx);
 		store_offset -= 8;
 	}
 
+	/* store TCC from RV_REG_TCC to stack */
+	emit_sd(RV_REG_SP, store_offset, RV_REG_TCC, ctx);
+	ctx->tcc_offset = store_offset;
+
 	emit_addi(RV_REG_FP, RV_REG_SP, stack_adjust, ctx);
 
 	if (bpf_stack_adjust)
 		emit_addi(RV_REG_S5, RV_REG_SP, bpf_stack_adjust, ctx);
 
-	/* Program contains calls and tail calls, so RV_REG_TCC need
-	 * to be saved across calls.
-	 */
-	if (seen_tail_call(ctx) && seen_call(ctx))
-		emit_mv(RV_REG_TCC_SAVED, RV_REG_TCC, ctx);
-
 	ctx->stack_size = stack_adjust;
 
 	if (ctx->arena_vm_start)
@@ -2157,3 +2151,8 @@ bool bpf_jit_supports_fsession(void)
 {
 	return true;
 }
+
+bool bpf_jit_supports_subprog_tailcalls(void)
+{
+	return true;
+}

arch/riscv/net/bpf_jit_core.c

@@ -72,7 +72,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
 	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 = kzalloc_objs(int, prog->len);
+	ctx->offset = kvzalloc_objs(int, prog->len);
 	if (!ctx->offset)
 		goto out_offset;
 
@@ -170,7 +170,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
 			ctx->offset[i] = ninsns_rvoff(ctx->offset[i]);
 		bpf_prog_fill_jited_linfo(prog, ctx->offset);
 out_offset:
-		kfree(ctx->offset);
+		kvfree(ctx->offset);
 		kfree(jit_data);
 		prog->aux->jit_data = NULL;
 	}
@@ -234,6 +234,7 @@ void bpf_jit_free(struct bpf_prog *prog)
 		 */
 		if (jit_data) {
 			bpf_jit_binary_pack_finalize(jit_data->ro_header, jit_data->header);
+			kvfree(jit_data->ctx.offset);
 			kfree(jit_data);
 		}
 		hdr = bpf_jit_binary_pack_hdr(prog);

include/linux/bpf.h

@@ -2196,6 +2196,12 @@ static inline bool is_tracing_multi(enum bpf_attach_type type)
 	       type == BPF_TRACE_FSESSION_MULTI;
 }
 
+static inline bool is_struct_ops_tramp(const struct bpf_tramp_nodes *fentry_nodes)
+{
+	return fentry_nodes->nr_nodes == 1 &&
+	       fentry_nodes->nodes[0]->link->type == BPF_LINK_TYPE_STRUCT_OPS;
+}
+
 #if defined(CONFIG_BPF_JIT) && defined(CONFIG_BPF_SYSCALL)
 /* This macro helps developer to register a struct_ops type and generate
  * type information correctly. Developers should use this macro to register

tools/testing/selftests/bpf/DENYLIST.riscv64

@@ -1,3 +1,2 @@
 # riscv64 deny list for BPF CI and local vmtest
 exceptions					# JIT does not support exceptions
-tailcalls/tailcall_bpf2bpf*			# JIT does not support mixing bpf2bpf and tailcalls