From dd691e847d28ac5f8b8e3005be44fd0e46722809 Mon Sep 17 00:00:00 2001 From: Ilya Leoshkevich Date: Sun, 29 Jan 2023 20:04:58 +0100 Subject: [PATCH] s390/bpf: Implement bpf_jit_supports_subprog_tailcalls() Allow mixing subprogs and tail calls by passing the current tail call count to subprogs. Signed-off-by: Ilya Leoshkevich Link: https://lore.kernel.org/r/20230129190501.1624747-6-iii@linux.ibm.com Signed-off-by: Alexei Starovoitov --- arch/s390/net/bpf_jit_comp.c | 37 +++++++++++++++++++++++++++---------- 1 file changed, 27 insertions(+), 10 deletions(-) diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index 3fe082d5328d..b84c7ddb758a 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -58,7 +58,6 @@ struct bpf_jit { #define SEEN_MEM BIT(0) /* use mem[] for temporary storage */ #define SEEN_LITERAL BIT(1) /* code uses literals */ #define SEEN_FUNC BIT(2) /* calls C functions */ -#define SEEN_TAIL_CALL BIT(3) /* code uses tail calls */ #define SEEN_STACK (SEEN_FUNC | SEEN_MEM) /* @@ -549,20 +548,23 @@ static void bpf_jit_plt(void *plt, void *ret, void *target) * Save registers and create stack frame if necessary. * See stack frame layout description in "bpf_jit.h"! */ -static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth) +static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp, + u32 stack_depth) { /* No-op for hotpatching */ /* brcl 0,prologue_plt */ EMIT6_PCREL_RILC(0xc0040000, 0, jit->prologue_plt); jit->prologue_plt_ret = jit->prg; - if (jit->seen & SEEN_TAIL_CALL) { + if (fp->aux->func_idx == 0) { + /* Initialize the tail call counter in the main program. */ /* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */ _EMIT6(0xd703f000 | STK_OFF_TCCNT, 0xf000 | STK_OFF_TCCNT); } else { /* - * There are no tail calls. Insert nops in order to have - * tail_call_start at a predictable offset. + * Skip the tail call counter initialization in subprograms. + * Insert nops in order to have tail_call_start at a + * predictable offset. */ bpf_skip(jit, 6); } @@ -1410,6 +1412,19 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, REG_SET_SEEN(BPF_REG_5); jit->seen |= SEEN_FUNC; + /* + * Copy the tail call counter to where the callee expects it. + * + * Note 1: The callee can increment the tail call counter, but + * we do not load it back, since the x86 JIT does not do this + * either. + * + * Note 2: We assume that the verifier does not let us call the + * main program, which clears the tail call counter on entry. + */ + /* mvc STK_OFF_TCCNT(4,%r15),N(%r15) */ + _EMIT6(0xd203f000 | STK_OFF_TCCNT, + 0xf000 | (STK_OFF_TCCNT + STK_OFF + stack_depth)); /* lgrl %w1,func */ EMIT6_PCREL_RILB(0xc4080000, REG_W1, _EMIT_CONST_U64(func)); /* %r1() */ @@ -1426,10 +1441,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, * B1: pointer to ctx * B2: pointer to bpf_array * B3: index in bpf_array - */ - jit->seen |= SEEN_TAIL_CALL; - - /* + * * if (index >= array->map.max_entries) * goto out; */ @@ -1793,7 +1805,7 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp, jit->prg = 0; jit->excnt = 0; - bpf_jit_prologue(jit, stack_depth); + bpf_jit_prologue(jit, fp, stack_depth); if (bpf_set_addr(jit, 0) < 0) return -1; for (i = 0; i < fp->len; i += insn_count) { @@ -2462,3 +2474,8 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, return ret; } + +bool bpf_jit_supports_subprog_tailcalls(void) +{ + return true; +} -- 2.11.0