Le 15/02/2022 à 14:36, Naveen N. Rao a écrit :
> Michael Ellerman wrote:
>> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
>>> Le 14/02/2022 à 16:25, Naveen N. Rao a écrit :
>>>> Christophe Leroy wrote:
>>>>> Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS. It accelerates the call
>>>>> of livepatching.
>>>>>
>>>>> Also note that powerpc being the last one to convert to
>>>>> CONFIG_DYNAMIC_FTRACE_WITH_ARGS, it will now be possible to remove
>>>>> klp_arch_set_pc() on all architectures.
>>>>>
>>>>> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
>>>>> ---
>>>>> arch/powerpc/Kconfig | 1 +
>>>>> arch/powerpc/include/asm/ftrace.h | 17 +++++++++++++++++
>>>>> arch/powerpc/include/asm/livepatch.h | 4 +---
>>>>> 3 files changed, 19 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>>>>> index cdac2115eb00..e2b1792b2aae 100644
>>>>> --- a/arch/powerpc/Kconfig
>>>>> +++ b/arch/powerpc/Kconfig
>>>>> @@ -210,6 +210,7 @@ config PPC
>>>>> select HAVE_DEBUG_KMEMLEAK
>>>>> select HAVE_DEBUG_STACKOVERFLOW
>>>>> select HAVE_DYNAMIC_FTRACE
>>>>> + select HAVE_DYNAMIC_FTRACE_WITH_ARGS if MPROFILE_KERNEL ||
>>>>> PPC32
>>>>> select HAVE_DYNAMIC_FTRACE_WITH_REGS if MPROFILE_KERNEL ||
>>>>> PPC32
>>>>> select HAVE_EBPF_JIT
>>>>> select HAVE_EFFICIENT_UNALIGNED_ACCESS if
>>>>> !(CPU_LITTLE_ENDIAN && POWER7_CPU)
>>>>> diff --git a/arch/powerpc/include/asm/ftrace.h
>>>>> b/arch/powerpc/include/asm/ftrace.h
>>>>> index b3f6184f77ea..45c3d6f11daa 100644
>>>>> --- a/arch/powerpc/include/asm/ftrace.h
>>>>> +++ b/arch/powerpc/include/asm/ftrace.h
>>>>> @@ -22,6 +22,23 @@ static inline unsigned long
>>>>> ftrace_call_adjust(unsigned long addr)
>>>>> struct dyn_arch_ftrace {
>>>>> struct module *mod;
>>>>> };
>>>>> +
>>>>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
>>>>> +struct ftrace_regs {
>>>>> + struct pt_regs regs;
>>>>> +};
>>>>> +
>>>>> +static __always_inline struct pt_regs *arch_ftrace_get_regs(struct
>>>>> ftrace_regs *fregs)
>>>>> +{
>>>>> + return &fregs->regs;
>>>>> +}
>>>>
>>>> I think this is wrong. We need to differentiate between
>>>> ftrace_caller() and ftrace_regs_caller() here, and only return
>>>> pt_regs if coming in through ftrace_regs_caller() (i.e.,
>>>> FL_SAVE_REGS is set).
>>>
>>> Not sure I follow you.
>>>
>>> This is based on 5740a7c71ab6 ("s390/ftrace: add
>>> HAVE_DYNAMIC_FTRACE_WITH_ARGS support")
>>>
>>> It's all the point of HAVE_DYNAMIC_FTRACE_WITH_ARGS, have the regs
>>> also with ftrace_caller().
>>>
>>> Sure you only have the params, but that's the same on s390, so what
>>> did I miss ?
>
> It looks like s390 is special since it apparently saves all registers
> even for ftrace_caller:
> https://lore.kernel.org/all/YbipdU5X4HNDWIni@osiris/
It is not what I understand from their code, see
https://elixir.bootlin.com/linux/v5.17-rc3/source/arch/s390/kernel/mcount.S#L37
They have a common macro called with argument 'allregs' which is set to
0 for ftrace_caller() and 1 for ftrace_regs_caller().
When allregs == 1, the macro seems to save more.
But ok, I can do like x86, but I need a trick to know whether
FL_SAVE_REGS is set or not, like they do with fregs->regs.cs
Any idea what the condition can be for powerpc ?
Thanks
Christophe
