nfp: bpf: add main logics for BPF-to-BPF calls support in nfp driver

This is the main patch for the logics of BPF-to-BPF calls in the nfp
driver.

The functions called on BPF_JUMP | BPF_CALL and BPF_JUMP | BPF_EXIT were
used to call helpers and exit from the program, respectively; make them
usable for calling into, or returning from, a BPF subprogram as well.

For all calls, push the return address as well as the callee-saved
registers (R6 to R9) to the stack, and pop them upon returning from the
calls. In order to limit the overhead in terms of instruction number,
this is done through dedicated subroutines. Jumping to the callee
actually consists in jumping to the subroutine, that "returns" to the
callee: this will require some fixup for passing the address in a later
patch. Similarly, returning consists in jumping to the subroutine, which
pops registers and then return directly to the caller (but no fixup is
needed here).

Return to the caller is performed with the RTN instruction newly added
to the JIT.

For the few steps where we need to know what subprogram an instruction
belongs to, the struct nfp_insn_meta is extended with a new subprog_idx
field.

Note that checks on the available stack size, to take into account the
additional requirements associated to BPF-to-BPF calls (storing R6-R9
and return addresses), are added in a later patch.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/net/ethernet/netronome/nfp/bpf/main.h b/drivers/net/ethernet/netronome/nfp/bpf/main.h
index 20a98ce4b345..d9695bc316dd 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/main.h
+++ b/drivers/net/ethernet/netronome/nfp/bpf/main.h
@@ -61,6 +61,8 @@ enum nfp_relo_type {
 	/* internal jumps to parts of the outro */
 	RELO_BR_GO_OUT,
 	RELO_BR_GO_ABORT,
+	RELO_BR_GO_CALL_PUSH_REGS,
+	RELO_BR_GO_CALL_POP_REGS,
 	/* external jumps to fixed addresses */
 	RELO_BR_NEXT_PKT,
 	RELO_BR_HELPER,
@@ -104,6 +106,7 @@ enum pkt_vec {
 #define imma_a(np)	reg_a(STATIC_REG_IMMA)
 #define imma_b(np)	reg_b(STATIC_REG_IMMA)
 #define imm_both(np)	reg_both(STATIC_REG_IMM)
+#define ret_reg(np)	imm_a(np)
 
 #define NFP_BPF_ABI_FLAGS	reg_imm(0)
 #define   NFP_BPF_ABI_FLAG_MARK	1
@@ -290,6 +293,7 @@ struct nfp_bpf_reg_state {
  * @off: index of first generated machine instruction (in nfp_prog.prog)
  * @n: eBPF instruction number
  * @flags: eBPF instruction extra optimization flags
+ * @subprog_idx: index of subprogram to which the instruction belongs
  * @skip: skip this instruction (optimized out)
  * @double_cb: callback for second part of the instruction
  * @l: link on nfp_prog->insns list
@@ -336,6 +340,7 @@ struct nfp_insn_meta {
 	unsigned int off;
 	unsigned short n;
 	unsigned short flags;
+	unsigned short subprog_idx;
 	bool skip;
 	instr_cb_t double_cb;
 
@@ -432,6 +437,16 @@ static inline bool is_mbpf_helper_call(const struct nfp_insn_meta *meta)
 		insn.src_reg != BPF_PSEUDO_CALL;
 }
 
+static inline bool is_mbpf_pseudo_call(const struct nfp_insn_meta *meta)
+{
+	struct bpf_insn insn = meta->insn;
+
+	return insn.code == (BPF_JMP | BPF_CALL) &&
+		insn.src_reg == BPF_PSEUDO_CALL;
+}
+
+#define STACK_FRAME_ALIGN 64
+
 /**
  * struct nfp_bpf_subprog_info - nfp BPF sub-program (a.k.a. function) info
  * @stack_depth:	maximum stack depth used by this sub-program
@@ -451,6 +466,8 @@ struct nfp_bpf_subprog_info {
  * @last_bpf_off: address of the last instruction translated from BPF
  * @tgt_out: jump target for normal exit
  * @tgt_abort: jump target for abort (e.g. access outside of packet buffer)
+ * @tgt_call_push_regs: jump target for subroutine for saving R6~R9 to stack
+ * @tgt_call_pop_regs: jump target for subroutine used for restoring R6~R9
  * @n_translated: number of successfully translated instructions (for errors)
  * @error: error code if something went wrong
  * @stack_frame_depth: max stack depth for current frame
@@ -475,6 +492,8 @@ struct nfp_prog {
 	unsigned int last_bpf_off;
 	unsigned int tgt_out;
 	unsigned int tgt_abort;
+	unsigned int tgt_call_push_regs;
+	unsigned int tgt_call_pop_regs;
 
 	unsigned int n_translated;
 	int error;
@@ -502,6 +521,7 @@ struct nfp_bpf_vnic {
 	unsigned int tgt_done;
 };
 
+bool nfp_is_subprog_start(struct nfp_insn_meta *meta);
 void nfp_bpf_jit_prepare(struct nfp_prog *nfp_prog, unsigned int cnt);
 int nfp_bpf_jit(struct nfp_prog *prog);
 bool nfp_bpf_supported_opcode(u8 code);