[PATCH v2 09/13] powerpc/ftrace: Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS
Naveen N. Rao
naveen.n.rao at linux.vnet.ibm.com
Wed Feb 16 03:25:52 AEDT 2022
Christophe Leroy wrote:
> + S390 people
>
> Le 15/02/2022 à 15:28, Christophe Leroy a écrit :
>>
>>
>> Le 15/02/2022 à 14:36, Naveen N. Rao a écrit :
>>> Michael Ellerman wrote:
>>>> Christophe Leroy <christophe.leroy at csgroup.eu> 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 at csgroup.eu>
>>>>>>> ---
>>>>>>> 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 ?
Steven has explained the rationale for this in his other response:
https://lore.kernel.org/all/20220215093849.556d5444@gandalf.local.home/
>>>
>>> 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 ?
We'll need to explicitly zero-out something in pt_regs in
ftrace_caller(). We can probably use regs->msr since we don't expect it
to be zero when saved from ftrace_regs_caller().
>>
>
> Finally, it looks like this change is done via commit 894979689d3a
> ("s390/ftrace: provide separate ftrace_caller/ftrace_regs_caller
> implementations") four hours the same day after the implementation of
> arch_ftrace_get_regs()
>
> They may have forgotten to change arch_ftrace_get_regs() which was added
> in commit 5740a7c71ab6 ("s390/ftrace: add HAVE_DYNAMIC_FTRACE_WITH_ARGS
> support") with the assumption that ftrace_caller and ftrace_regs_caller
> where identical.
Indeed, good find!
Thanks,
Naveen
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