Re: [PATCH v2 1/5] powerpc64/bpf: do not increment tailcall count when prog is NULL

Do not increment tailcall count, if tailcall did not succeed due to
missing BPF program.

Fixes: ce0761419fae ("powerpc/bpf: Implement support for tail calls")
Cc: stable@vger.kernel.org
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---

* No changes since v1.


  arch/powerpc/net/bpf_jit_comp64.c | 39 +++++++++++++++++--------------
  1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index b1a3945ccc9f..44ce8a8783f9 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c

@@ -522,9 +522,30 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
  
  	/*
  	 * tail_call_info++; <- Actual value of tcc here
+	 * Writeback this updated value only if tailcall succeeds.
  	 */
  	EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), 1));
  
+	/* prog = array->ptrs[index]; */
+	EMIT(PPC_RAW_MULI(bpf_to_ppc(TMP_REG_2), b2p_index, 8));
+	EMIT(PPC_RAW_ADD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2), b2p_bpf_array));
+	EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+			offsetof(struct bpf_array, ptrs)));
+
+	/*
+	 * if (prog == NULL)
+	 *   goto out;
+	 */
+	EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_2), 0));
+	PPC_BCC_SHORT(COND_EQ, out);
+
+	/* goto *(prog->bpf_func + prologue_size); */
+	EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+			offsetof(struct bpf_prog, bpf_func)));
+	EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_2), bpf_to_ppc(TMP_REG_2),
+			  FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
+	EMIT(PPC_RAW_MTCTR(bpf_to_ppc(TMP_REG_2)));
+
  	/*
  	 * Before writing updated tail_call_info, distinguish if current frame
  	 * is storing a reference to tail_call_info or actual tcc value in

@@ -539,24 +560,6 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
  	/* Writeback updated value to tail_call_info */
  	EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_2), 0));
  
-	/* prog = array->ptrs[index]; */
-	EMIT(PPC_RAW_MULI(bpf_to_ppc(TMP_REG_1), b2p_index, 8));
-	EMIT(PPC_RAW_ADD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), b2p_bpf_array));
-	EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), offsetof(struct bpf_array, ptrs)));
-
-	/*
-	 * if (prog == NULL)
-	 *   goto out;
-	 */
-	EMIT(PPC_RAW_CMPLDI(bpf_to_ppc(TMP_REG_1), 0));
-	PPC_BCC_SHORT(COND_EQ, out);
-
-	/* goto *(prog->bpf_func + prologue_size); */
-	EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), offsetof(struct bpf_prog, bpf_func)));
-	EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1),
-			FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
-	EMIT(PPC_RAW_MTCTR(bpf_to_ppc(TMP_REG_1)));
-
  	/* tear down stack, restore NVRs, ... */
  	bpf_jit_emit_common_epilogue(image, ctx);