Re: [PATCH v6 17/17] powerpc64/bpf: Add support for bpf trampolines

[Michael Ellerman <mpe@ellerman.id.au>]

Hari Bathini <hbathini@linux.ibm.com> writes:
> From: Naveen N Rao <naveen@kernel.org>
>
> Add support for bpf_arch_text_poke() and arch_prepare_bpf_trampoline()
> for 64-bit powerpc. While the code is generic, BPF trampolines are only
> enabled on 64-bit powerpc. 32-bit powerpc will need testing and some
> updates.

Hi Hari,

This is breaking the PCREL build for me:

  ERROR: 11:49:18: Failed building ppc64le_defconfig+pcrel@fedora
  INFO: 11:49:18: (skipped 41 lines) ...
  INFO: 11:49:18: /linux/arch/powerpc/net/bpf_jit.h:90:9: note: in expansion of macro 'EMIT'
     90 |         EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
        |         ^~~~
  /linux/arch/powerpc/include/asm/ppc-opcode.h:473:88: note: in expansion of macro 'IMM_DS'
    473 | #define PPC_RAW_LD(r, base, i)          (0xe8000000 | ___PPC_RT(r) | ___PPC_RA(base) | IMM_DS(i))
        |                                                                                        ^~~~~~
  /linux/arch/powerpc/net/bpf_jit.h:90:14: note: in expansion of macro 'PPC_RAW_LD'
     90 |         EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
        |              ^~~~~~~~~~
  /linux/arch/powerpc/net/bpf_jit.h:90:36: note: in expansion of macro 'offsetof'
     90 |         EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
        |                                    ^~~~~~~~
  /linux/arch/powerpc/net/bpf_jit_comp.c:791:17: note: in expansion of macro 'PPC64_LOAD_PACA'
    791 |                 PPC64_LOAD_PACA();
        |                 ^~~~~~~~~~~~~~~
  /linux/arch/powerpc/net/bpf_jit.h:90:65: error: 'struct paca_struct' has no member named 'kernel_toc'; did you mean 'kernel_msr'?
     90 |         EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
        |                                                                 ^~~~~~~~~~
  /linux/arch/powerpc/net/bpf_jit.h:29:34: note: in definition of macro 'PLANT_INSTR'
     29 |         do { if (d) { (d)[idx] = instr; } idx++; } while (0)
        |                                  ^~~~~
  /linux/arch/powerpc/net/bpf_jit.h:90:9: note: in expansion of macro 'EMIT'
     90 |         EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
        |         ^~~~
  /linux/arch/powerpc/include/asm/ppc-opcode.h:473:88: note: in expansion of macro 'IMM_DS'
    473 | #define PPC_RAW_LD(r, base, i)          (0xe8000000 | ___PPC_RT(r) | ___PPC_RA(base) | IMM_DS(i))
        |                                                                                        ^~~~~~
  /linux/arch/powerpc/net/bpf_jit.h:90:14: note: in expansion of macro 'PPC_RAW_LD'
     90 |         EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
        |              ^~~~~~~~~~
  /linux/arch/powerpc/net/bpf_jit.h:90:36: note: in expansion of macro 'offsetof'
     90 |         EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
        |                                    ^~~~~~~~
  /linux/arch/powerpc/net/bpf_jit_comp.c:882:25: note: in expansion of macro 'PPC64_LOAD_PACA'
    882 |                         PPC64_LOAD_PACA();
        |                         ^~~~~~~~~~~~~~~
  make[5]: *** [/linux/scripts/Makefile.build:229: arch/powerpc/net/bpf_jit_comp.o] Error 1


To test it you need to enable CONFIG_POWER10_CPU, eg:

  CONFIG_POWERPC64_CPU=n
  CONFIG_POWER10_CPU=y
  CONFIG_PPC_KERNEL_PCREL=y

This diff gets it building, but I haven't tested it actually works:

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 2d04ce5a23da..af6ff3eb621a 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -86,9 +86,14 @@
                                                        0xffff));             \
                } } while (0)
 #define PPC_LI_ADDR    PPC_LI64
+
+#ifndef CONFIG_PPC_KERNEL_PCREL
 #define PPC64_LOAD_PACA()                                                    \
        EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)))
 #else
+#define PPC64_LOAD_PACA() do {} while (0)
+#endif
+#else
 #define PPC_LI64(d, i) BUILD_BUG()
 #define PPC_LI_ADDR    PPC_LI32
 #define PPC64_LOAD_PACA() BUILD_BUG()

cheers