[RFC PATCH v3 10/11] powerpc64/bpf: Fold bpf_jit_emit_func_call_hlp() into bpf_jit_emit_func_call_rel()

Naveen N Rao
2024-06-20T19:09:42Z

Commit 61688a82e047 ("powerpc/bpf: enable kfunc call") enhanced
bpf_jit_emit_func_call_hlp() to handle calls out to module region, where
bpf progs are generated. The only difference now between
bpf_jit_emit_func_call_hlp() and bpf_jit_emit_func_call_rel() is in
handling of the initial pass where target function address is not known.
Fold that logic into bpf_jit_emit_func_call_hlp() and rename it to
bpf_jit_emit_func_call_rel() to simplify bpf function call JIT code.

We don't actually need to load/restore TOC across a call out to a
different kernel helper or to a different bpf program since they all
work with the kernel TOC. We only need to do it if we have to call out
to a module function. So, guard TOC load/restore with appropriate
conditions.

Signed-off-by: Naveen N Rao <naveen@kernel.org>
---
arch/powerpc/net/bpf_jit_comp64.c | 61 +++++++++----------------------
1 file changed, 17 insertions(+), 44 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 7703dcf48be8..288ff32d676f 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -202,14 +202,22 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
EMIT(PPC_RAW_BLR());
}

-static int
-bpf_jit_emit_func_call_hlp(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func)
+int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func)
{
unsigned long func_addr = func ? ppc_function_entry((void *)func) : 0;
long reladdr;

- if (WARN_ON_ONCE(!kernel_text_address(func_addr)))
- return -EINVAL;
+ /* bpf to bpf call, func is not known in the initial pass. Emit 5 nops as a placeholder */
+ if (!func) {
+ for (int i = 0; i < 5; i++)
+ EMIT(PPC_RAW_NOP());
+ /* elfv1 needs an additional instruction to load addr from descriptor */
+ if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1))
+ EMIT(PPC_RAW_NOP());
+ EMIT(PPC_RAW_MTCTR(_R12));
+ EMIT(PPC_RAW_BCTRL());
+ return 0;
+ }

#ifdef CONFIG_PPC_KERNEL_PCREL
reladdr = func_addr - local_paca->kernelbase;
@@ -266,7 +274,8 @@ bpf_jit_emit_func_call_hlp(u32 *image, u32 *fimage, struct codegen_context *ctx,
* We can clobber r2 since we get called through a
* function pointer (so caller will save/restore r2).
*/
- EMIT(PPC_RAW_LD(_R2, bpf_to_ppc(TMP_REG_2), 8));
+ if (is_module_text_address(func_addr))
+ EMIT(PPC_RAW_LD(_R2, bpf_to_ppc(TMP_REG_2), 8));
} else {
PPC_LI64(_R12, func);
EMIT(PPC_RAW_MTCTR(_R12));
@@ -276,46 +285,14 @@ bpf_jit_emit_func_call_hlp(u32 *image, u32 *fimage, struct codegen_context *ctx,
* Load r2 with kernel TOC as kernel TOC is used if function address falls
* within core kernel text.
*/
- EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)));
+ if (is_module_text_address(func_addr))
+ EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)));
}
#endif

return 0;
}

-int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func)
-{
- unsigned int i, ctx_idx = ctx->idx;
-
- if (WARN_ON_ONCE(func && is_module_text_address(func)))
- return -EINVAL;
-
- /* skip past descriptor if elf v1 */
- func += FUNCTION_DESCR_SIZE;
-
- /* Load function address into r12 */
- PPC_LI64(_R12, func);
-
- /* For bpf-to-bpf function calls, the callee's address is unknown
- * until the last extra pass. As seen above, we use PPC_LI64() to
- * load the callee's address, but this may optimize the number of
- * instructions required based on the nature of the address.
- *
- * Since we don't want the number of instructions emitted to increase,
- * we pad the optimized PPC_LI64() call with NOPs to guarantee that
- * we always have a five-instruction sequence, which is the maximum
- * that PPC_LI64() can emit.
- */
- if (!image)
- for (i = ctx->idx - ctx_idx; i < 5; i++)
- EMIT(PPC_RAW_NOP());
-
- EMIT(PPC_RAW_MTCTR(_R12));
- EMIT(PPC_RAW_BCTRL());
-
- return 0;
-}
-
static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 out)
{
/*
@@ -1047,11 +1024,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
if (ret < 0)
return ret;

- if (func_addr_fixed)
- ret = bpf_jit_emit_func_call_hlp(image, fimage, ctx, func_addr);
- else
- ret = bpf_jit_emit_func_call_rel(image, fimage, ctx, func_addr);
-
+ ret = bpf_jit_emit_func_call_rel(image, fimage, ctx, func_addr);
if (ret)
return ret;

--
2.45.2