From: Abhishek Dubey <[email protected]> In the conventional stack frame, the position of tail_call_cnt is after the NVR save area (BPF_PPC_STACK_SAVE). Whereas, the offset of tail_call_cnt in the trampoline frame is after the stack alignment padding. BPF JIT logic could become complex when dealing with frame-sensitive offset calculation of tail_call_cnt. Having the same offset in both frames is the desired objective.
The trampoline frame does not have a BPF_PPC_STACK_SAVE area. Introducing it leads to under-utilization of extra memory meant only for the offset alignment of tail_call_cnt. Another challenge is the variable alignment padding sitting at the bottom of the trampoline frame, which requires additional handling to compute tail_call_cnt offset. This patch addresses the above issues by moving tail_call_cnt to the bottom of the stack frame at offset 0 for both types of frames. This saves additional bytes required by BPF_PPC_STACK_SAVE in trampoline frame, and a common offset computation for tail_call_cnt serves both frames. The changes in this patch are required by the third patch in the series, where the 'reference to tail_call_info' of the main frame is copied into the trampoline frame from the previous frame. Signed-off-by: Abhishek Dubey <[email protected]> --- arch/powerpc/net/bpf_jit.h | 4 ++++ arch/powerpc/net/bpf_jit_comp64.c | 31 ++++++++++++++++++++----------- 2 files changed, 24 insertions(+), 11 deletions(-) diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h index 8334cd667bba..45d419c0ee73 100644 --- a/arch/powerpc/net/bpf_jit.h +++ b/arch/powerpc/net/bpf_jit.h @@ -72,6 +72,10 @@ } } while (0) #ifdef CONFIG_PPC64 + +/* for tailcall counter */ +#define BPF_PPC_TAILCALL 8 + /* If dummy pass (!image), account for maximum possible instructions */ #define PPC_LI64(d, i) do { \ if (!image) \ diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index 1fe37128c876..39061cd742c1 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -20,13 +20,15 @@ #include "bpf_jit.h" /* - * Stack layout: + * Stack layout 1: + * Layout when setting up our own stack frame. + * Note: r1 at bottom, component offsets positive wrt r1. * Ensure the top half (upto local_tmp_var) stays consistent * with our redzone usage. * * [ prev sp ] <------------- - * [ nv gpr save area ] 6*8 | * [ tail_call_cnt ] 8 | + * [ nv gpr save area ] 6*8 | * [ local_tmp_var ] 24 | * fp (r31) --> [ ebpf stack space ] upto 512 | * [ frame header ] 32/112 | @@ -36,10 +38,12 @@ /* for gpr non volatile registers BPG_REG_6 to 10 */ #define BPF_PPC_STACK_SAVE (6*8) /* for bpf JIT code internal usage */ -#define BPF_PPC_STACK_LOCALS 32 +#define BPF_PPC_STACK_LOCALS 24 /* stack frame excluding BPF stack, ensure this is quadword aligned */ #define BPF_PPC_STACKFRAME (STACK_FRAME_MIN_SIZE + \ - BPF_PPC_STACK_LOCALS + BPF_PPC_STACK_SAVE) + BPF_PPC_STACK_LOCALS + \ + BPF_PPC_STACK_SAVE + \ + BPF_PPC_TAILCALL) /* BPF register usage */ #define TMP_REG_1 (MAX_BPF_JIT_REG + 0) @@ -87,27 +91,32 @@ static inline bool bpf_has_stack_frame(struct codegen_context *ctx) } /* + * Stack layout 2: * When not setting up our own stackframe, the redzone (288 bytes) usage is: + * Note: r1 from prev frame. Component offset negative wrt r1. * * [ prev sp ] <------------- * [ ... ] | * sp (r1) ---> [ stack pointer ] -------------- - * [ nv gpr save area ] 6*8 * [ tail_call_cnt ] 8 + * [ nv gpr save area ] 6*8 * [ local_tmp_var ] 24 * [ unused red zone ] 224 */ static int bpf_jit_stack_local(struct codegen_context *ctx) { - if (bpf_has_stack_frame(ctx)) + if (bpf_has_stack_frame(ctx)) { + /* Stack layout 1 */ return STACK_FRAME_MIN_SIZE + ctx->stack_size; - else - return -(BPF_PPC_STACK_SAVE + 32); + } else { + /* Stack layout 2 */ + return -(BPF_PPC_TAILCALL + BPF_PPC_STACK_SAVE + BPF_PPC_STACK_LOCALS); + } } static int bpf_jit_stack_tailcallcnt(struct codegen_context *ctx) { - return bpf_jit_stack_local(ctx) + 24; + return bpf_jit_stack_local(ctx) + BPF_PPC_STACK_LOCALS + BPF_PPC_STACK_SAVE; } static int bpf_jit_stack_offsetof(struct codegen_context *ctx, int reg) @@ -115,7 +124,7 @@ static int bpf_jit_stack_offsetof(struct codegen_context *ctx, int reg) if (reg >= BPF_PPC_NVR_MIN && reg < 32) return (bpf_has_stack_frame(ctx) ? (BPF_PPC_STACKFRAME + ctx->stack_size) : 0) - - (8 * (32 - reg)); + - (8 * (32 - reg)) - BPF_PPC_TAILCALL; pr_err("BPF JIT is asking about unknown registers"); BUG(); @@ -145,7 +154,7 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx) if (ctx->seen & SEEN_TAILCALL) { EMIT(PPC_RAW_LI(bpf_to_ppc(TMP_REG_1), 0)); /* this goes in the redzone */ - EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, -(BPF_PPC_STACK_SAVE + 8))); + EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, -(BPF_PPC_TAILCALL))); } else { EMIT(PPC_RAW_NOP()); EMIT(PPC_RAW_NOP()); -- 2.48.1
