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

[Hari Bathini <hbathini@linux.ibm.com>]

On 28/10/24 7:53 am, Michael Ellerman wrote:
> 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:

Thanks, Michael. Yeah, the below snippet will be sufficient as
PPC64_LOAD_PACA() is used with !IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)

- Hari

> 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
>