[PATCH 5.15-5.10] powerpc64/bpf: do not increment tailcall count when prog is NULL

[PATCH 5.15-5.10] powerpc64/bpf: do not increment tailcall count when prog is NULL

[Hari Bathini]

[ Upstream commit 521bd39d9d28ce54cbfec7f9b89c94ad4fdb8350 ]

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
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260303181031.390073-2-hbathini@linux.ibm.com
[ Conflicts due to missing clean up commits
    b10cb163c4b3 ("powerpc64/bpf elfv2: Setup kernel TOC in r2 on entry")
    49c3af43e65f ("powerpc/bpf:   Simplify bpf_to_ppc() and adopt it for powerpc64")
    036d559c0bde ("powerpc/bpf: Use _Rn macros for GPRs")
  and missing feature commit 2ed2d8f6fb38 ("powerpc64/bpf: Support
  tailcalls with subprogs") resolved accordingly. ]
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 arch/powerpc/net/bpf_jit_comp64.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 57e1b6680365..6f4a7bcf53aa 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -239,30 +239,32 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 	 * tail_call_cnt++;
 	 */
 	EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], b2p[TMP_REG_1], 1));
-	PPC_BPF_STL(b2p[TMP_REG_1], 1, bpf_jit_stack_tailcallcnt(ctx));
 
 	/* prog = array->ptrs[index]; */
-	EMIT(PPC_RAW_MULI(b2p[TMP_REG_1], b2p_index, 8));
-	EMIT(PPC_RAW_ADD(b2p[TMP_REG_1], b2p[TMP_REG_1], b2p_bpf_array));
-	PPC_BPF_LL(b2p[TMP_REG_1], b2p[TMP_REG_1], offsetof(struct bpf_array, ptrs));
+	EMIT(PPC_RAW_MULI(b2p[TMP_REG_2], b2p_index, 8));
+	EMIT(PPC_RAW_ADD(b2p[TMP_REG_2], b2p[TMP_REG_2], b2p_bpf_array));
+	PPC_BPF_LL(b2p[TMP_REG_2], b2p[TMP_REG_2], offsetof(struct bpf_array, ptrs));
 
 	/*
 	 * if (prog == NULL)
 	 *   goto out;
 	 */
-	EMIT(PPC_RAW_CMPLDI(b2p[TMP_REG_1], 0));
+	EMIT(PPC_RAW_CMPLDI(b2p[TMP_REG_2], 0));
 	PPC_BCC(COND_EQ, out);
 
 	/* goto *(prog->bpf_func + prologue_size); */
-	PPC_BPF_LL(b2p[TMP_REG_1], b2p[TMP_REG_1], offsetof(struct bpf_prog, bpf_func));
+	PPC_BPF_LL(b2p[TMP_REG_2], b2p[TMP_REG_2], offsetof(struct bpf_prog, bpf_func));
 #ifdef PPC64_ELF_ABI_v1
 	/* skip past the function descriptor */
-	EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], b2p[TMP_REG_1],
+	EMIT(PPC_RAW_ADDI(b2p[TMP_REG_2], b2p[TMP_REG_2],
 			FUNCTION_DESCR_SIZE + BPF_TAILCALL_PROLOGUE_SIZE));
 #else
-	EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], b2p[TMP_REG_1], BPF_TAILCALL_PROLOGUE_SIZE));
+	EMIT(PPC_RAW_ADDI(b2p[TMP_REG_2], b2p[TMP_REG_2], BPF_TAILCALL_PROLOGUE_SIZE));
 #endif
-	EMIT(PPC_RAW_MTCTR(b2p[TMP_REG_1]));
+	EMIT(PPC_RAW_MTCTR(b2p[TMP_REG_2]));
+
+	/* Writeback updated tailcall count */
+	PPC_BPF_STL(b2p[TMP_REG_1], 1, bpf_jit_stack_tailcallcnt(ctx));
 
 	/* tear down stack, restore NVRs, ... */
 	bpf_jit_emit_common_epilogue(image, ctx);
-- 
2.53.0