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
WARNING: multiple messages have this Message-ID (diff)
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: "live-patching@vger.kernel.org" <live-patching@vger.kernel.org>, "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>, "linux-kernel@vger.kernel.org" <linux-kernel@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: 84+ 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 16:37 ` Christophe Leroy 2021-12-20 16:38 ` [PATCH v2 01/13] livepatch: Fix build failure on 32 bits processors Christophe Leroy 2021-12-20 16:38 ` Christophe Leroy 2021-12-22 13:47 ` Miroslav Benes 2021-12-22 13:47 ` Miroslav Benes 2022-01-04 19:35 ` Joe Lawrence 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 2021-12-20 16:38 ` Christophe Leroy 2022-02-24 13:43 ` Christophe Leroy 2022-02-24 13:43 ` Christophe Leroy 2022-02-24 14:53 ` Steven Rostedt 2022-02-24 14:53 ` Steven Rostedt 2022-02-24 15:13 ` Christophe Leroy 2022-02-24 15:13 ` Christophe Leroy 2022-02-24 15:17 ` Steven Rostedt 2022-02-24 15:17 ` Steven Rostedt 2022-02-25 2:42 ` Michael Ellerman 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 2021-12-20 16:38 ` Christophe Leroy 2022-01-04 19:44 ` Joe Lawrence 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 2021-12-20 16:38 ` Christophe Leroy 2021-12-22 14:00 ` Miroslav Benes 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 ` 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 ` 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 ` Christophe Leroy 2021-12-20 16:38 ` [PATCH v2 08/13] powerpc/ftrace: Prepare PPC64's " Christophe Leroy 2021-12-20 16:38 ` Christophe Leroy 2022-02-14 15:19 ` Naveen N. Rao 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 2021-12-20 16:38 ` Christophe Leroy 2021-12-22 14:19 ` Miroslav Benes 2021-12-22 14:19 ` Miroslav Benes 2021-12-22 14:19 ` Miroslav Benes 2022-02-14 15:25 ` Naveen N. Rao 2022-02-14 15:25 ` Naveen N. Rao 2022-02-15 8:00 ` Christophe Leroy 2022-02-15 8:00 ` Christophe Leroy 2022-02-15 11:05 ` Michael Ellerman [this message] 2022-02-15 11:05 ` Michael Ellerman 2022-02-15 13:36 ` Naveen N. Rao 2022-02-15 13:36 ` Naveen N. Rao 2022-02-15 14:28 ` Christophe Leroy 2022-02-15 14:28 ` Christophe Leroy 2022-02-15 14:51 ` Christophe Leroy 2022-02-15 14:51 ` Christophe Leroy 2022-02-15 16:25 ` Naveen N. Rao 2022-02-15 16:25 ` Naveen N. Rao 2022-02-16 13:04 ` Heiko Carstens 2022-02-16 13:04 ` Heiko Carstens 2022-02-16 13:27 ` Sven Schnelle 2022-02-16 13:27 ` Sven Schnelle 2022-02-15 14:38 ` Steven Rostedt 2022-02-15 14:38 ` Steven Rostedt 2022-02-15 16:26 ` Naveen N. Rao 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 ` Christophe Leroy 2021-12-20 16:38 ` [PATCH v2 11/13] powerpc/ftrace: directly call of function graph tracer by ftrace caller Christophe Leroy 2021-12-20 16:38 ` Christophe Leroy 2022-02-14 17:24 ` Naveen N. Rao 2022-02-14 17:24 ` Naveen N. Rao 2022-02-14 19:03 ` Steven Rostedt 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 2021-12-20 16:38 ` Christophe Leroy 2022-02-14 17:51 ` Naveen N. Rao 2022-02-14 17:51 ` Naveen N. Rao 2022-02-15 8:33 ` Christophe Leroy 2022-02-15 8:33 ` Christophe Leroy 2021-12-20 16:38 ` [PATCH v2 13/13] powerpc/ftrace: Remove ftrace_32.S Christophe Leroy 2021-12-20 16:38 ` Christophe Leroy 2022-02-11 7:41 ` [PATCH] Fixup for next-test 3a1a8f078670 ("powerpc/ftrace: Remove ftrace_32.S") Christophe Leroy 2022-02-11 7:41 ` Christophe Leroy 2022-02-16 12:26 ` [PATCH v2 00/13] Implement livepatch on PPC32 and more Michael Ellerman
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