From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Jiri Kosina <jikos@kernel.org>,
Joe Lawrence <joe.lawrence@redhat.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Miroslav Benes <mbenes@suse.cz>, Ingo Molnar <mingo@redhat.com>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"live-patching@vger.kernel.org" <live-patching@vger.kernel.org>
Subject: Re: [PATCH v2 09/13] powerpc/ftrace: Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS
Date: Tue, 15 Feb 2022 22:05:04 +1100 [thread overview]
Message-ID: <875ypgo0f3.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <1b28f52a-f8b7-6b5c-e726-feac4123517d@csgroup.eu>
Christophe Leroy <christophe.leroy@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@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 ?
I already have this series in next, I can pull it out, but I'd rather
not.
I'll leave it in for now, hopefully you two can agree overnight my time
whether this is a big problem or something we can fix with a fixup
patch.
>>> +static __always_inline void ftrace_instruction_pointer_set(struct
>>> ftrace_regs *fregs,
>>> + unsigned long ip)
>>> +{
>>> + regs_set_return_ip(&fregs->regs, ip);
>>
>> Should we use that helper here? regs_set_return_ip() also updates some
>> other state related to taking interrupts and I don't think it makes
>> sense for use with ftrace.
>
>
> Today we have:
>
> static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned
> long ip)
> {
> struct pt_regs *regs = ftrace_get_regs(fregs);
>
> regs_set_return_ip(regs, ip);
> }
>
>
> Which like x86 and s390 becomes:
>
> static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned
> long ip)
> {
> ftrace_instruction_pointer_set(fregs, ip);
> }
>
>
>
> That's the reason why I've been using regs_set_return_ip(). Do you think
> it was wrong to use regs_set_return_ip() in klp_arch_set_pc() ?
>
> That was added by 59dc5bfca0cb ("powerpc/64s: avoid reloading (H)SRR
> registers if they are still valid")
It's not wrong, but I think it's unnecessary. We need to use
regs_set_return_ip() if we're changing the regs->ip of an interrupt
frame, so that the interrupt return code will reload it.
But AIUI in this case we're not doing that, we're changing the regs->ip
of a pt_regs provided by ftrace, which shouldn't ever be an interrupt
frame.
So it's not a bug to use regs_set_return_ip(), but it is unncessary and
means we'll reload the interrupt state unnecessarily on the next
interrupt return.
cheers
next prev parent reply other threads:[~2022-02-15 11:05 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-20 16:37 [PATCH v2 00/13] Implement livepatch on PPC32 and more Christophe Leroy
2021-12-20 16:38 ` [PATCH v2 01/13] livepatch: Fix build failure on 32 bits processors Christophe Leroy
2021-12-22 13:47 ` Miroslav Benes
2022-01-04 19:35 ` Joe Lawrence
2021-12-20 16:38 ` [PATCH v2 02/13] tracing: Fix selftest config check for function graph start up test Christophe Leroy
2022-02-24 13:43 ` Christophe Leroy
2022-02-24 14:53 ` Steven Rostedt
2022-02-24 15:13 ` Christophe Leroy
2022-02-24 15:17 ` Steven Rostedt
2022-02-25 2:42 ` Michael Ellerman
2021-12-20 16:38 ` [PATCH v2 03/13] powerpc/module_32: Fix livepatching for RO modules Christophe Leroy
2022-01-04 19:44 ` Joe Lawrence
2021-12-20 16:38 ` [PATCH v2 04/13] powerpc/ftrace: Add support for livepatch to PPC32 Christophe Leroy
2021-12-22 14:00 ` Miroslav Benes
2021-12-20 16:38 ` [PATCH v2 05/13] powerpc/ftrace: Don't save again LR in ftrace_regs_caller() on PPC32 Christophe Leroy
2021-12-20 16:38 ` [PATCH v2 06/13] powerpc/ftrace: Simplify PPC32's return_to_handler() Christophe Leroy
2021-12-20 16:38 ` [PATCH v2 07/13] powerpc/ftrace: Prepare PPC32's ftrace_caller() for CONFIG_DYNAMIC_FTRACE_WITH_ARGS Christophe Leroy
2021-12-20 16:38 ` [PATCH v2 08/13] powerpc/ftrace: Prepare PPC64's " Christophe Leroy
2022-02-14 15:19 ` Naveen N. Rao
2021-12-20 16:38 ` [PATCH v2 09/13] powerpc/ftrace: Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS Christophe Leroy
2021-12-22 14:19 ` Miroslav Benes
2022-02-14 15:25 ` Naveen N. Rao
2022-02-15 8:00 ` Christophe Leroy
2022-02-15 11:05 ` Michael Ellerman [this message]
2022-02-15 13:36 ` Naveen N. Rao
2022-02-15 14:28 ` Christophe Leroy
2022-02-15 14:51 ` Christophe Leroy
2022-02-15 16:25 ` Naveen N. Rao
2022-02-16 13:04 ` Heiko Carstens
2022-02-16 13:27 ` Sven Schnelle
2022-02-15 14:38 ` Steven Rostedt
2022-02-15 16:26 ` Naveen N. Rao
2021-12-20 16:38 ` [PATCH v2 10/13] powerpc/ftrace: Refactor ftrace_{en/dis}able_ftrace_graph_caller Christophe Leroy
2021-12-20 16:38 ` [PATCH v2 11/13] powerpc/ftrace: directly call of function graph tracer by ftrace caller Christophe Leroy
2022-02-14 17:24 ` Naveen N. Rao
2022-02-14 19:03 ` Steven Rostedt
2021-12-20 16:38 ` [PATCH v2 12/13] powerpc/ftrace: Prepare ftrace_64_mprofile.S for reuse by PPC32 Christophe Leroy
2022-02-14 17:51 ` Naveen N. Rao
2022-02-15 8:33 ` Christophe Leroy
2021-12-20 16:38 ` [PATCH v2 13/13] powerpc/ftrace: Remove ftrace_32.S Christophe Leroy
2022-02-11 7:41 ` [PATCH] Fixup for next-test 3a1a8f078670 ("powerpc/ftrace: Remove ftrace_32.S") Christophe Leroy
2022-02-16 12:26 ` [PATCH v2 00/13] Implement livepatch on PPC32 and more Michael Ellerman
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